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Sample records for ablation dynamics model

  1. Dynamical modeling of laser ablation processes

    SciTech Connect

    Leboeuf, J.N.; Chen, K.R.; Donato, J.M.; Geohegan, D.B.; Liu, C.L.; Puretzky, A.A.; Wood, R.F.

    1995-09-01

    Several physics and computational approaches have been developed to globally characterize phenomena important for film growth by pulsed laser deposition of materials. These include thermal models of laser-solid target interactions that initiate the vapor plume; plume ionization and heating through laser absorption beyond local thermodynamic equilibrium mechanisms; gas dynamic, hydrodynamic, and collisional descriptions of plume transport; and molecular dynamics models of the interaction of plume particles with the deposition substrate. The complexity of the phenomena involved in the laser ablation process is matched by the diversity of the modeling task, which combines materials science, atomic physics, and plasma physics.

  2. Modeling of dynamical processes in laser ablation

    SciTech Connect

    Leboeuf, J.N.; Chen, K.R.; Donato, J.M.; Geohegan, D.B.; Liu, C.L.; Puretzky, A.A.; Wood, R.F.

    1995-12-31

    Various physics and computational approaches have been developed to globally characterize phenomena important for film growth by pulsed-laser deposition of materials. These include thermal models of laser-solid target interactions that initiate the vapor plume, plume ionization and heating through laser absorption beyond local thermodynamic equilibrium mechanisms, hydrodynamic and collisional descriptions of plume transport, and molecular dynamics models of the interaction of plume particles with the deposition substrate.

  3. Modeling of plume dynamics in laser ablation processes for thin film deposition of materials

    SciTech Connect

    Leboeuf, J.N.; Chen, K.R.; Donato, J.M.; Geohegan, D.B.; Liu, C.L.; Puretzky, A.A.; Wood, R.F.

    1995-12-31

    The transport dynamics of laser-ablated neutral/plasma plumes are of significant interest for film growth by pulsed-laser deposition of materials since the magnitude and kinetic energy of the species arriving at the deposition substrate are key processing parameters. Dynamical calculations of plume propagation in vacuum and in background gas have been performed using particle-in-cell hydrodynamics, continuum gas dynamics, and scattering models. Results from these calculations are presented and compared with experimental observations.

  4. Combined thermal and gas dynamics numerical model for laser ablation of carbon.

    PubMed

    Pathak, Kedar; Mullenix, Nathan; Povitsky, Alex

    2006-05-01

    One of the major methods of production of carbon nanotubes is the laser ablation process. In this process, a powerful nanosecond-scale laser beam illuminates a target. The resulting explosion produces a plume of rapidly expanding gaseous carbon with embedded metallic catalysts, on whose surfaces the nanotubes are formed. The time-scale of a single laser pulse is of the order of nanoseconds whereas the plume development and growth of nanotubes take up to several milliseconds. The synthesis process largely depends on the plume properties, i.e., on the temperature, pressure, and density of the expanding plume. In turn, the plume propagation depends on the ablation speed, pressure, and density. In the current study, a combined thermal and gas dynamics model is proposed, implemented and tested. The proposed model is based on combined conduction heat transfer within the solid target, carbon sublimation process described by equilibrium thermodynamics, and process of plume development described by continuous gas dynamics. The carbon sublimation model is based on Clausius-Clapeyron equation and conservation of energy for differential control volume. The parameters of the injected plume are defined by this thermal model. The validity of viscous and inviscid models of plume dynamics is discussed. The ability of finite-volume discretizations to capture the plume dynamics and its roll-up is compared for various numerical schemes. To evaluate the accuracy of numerical modeling of plume dynamics, we compare finite-volume discretization based on Relaxing TVD scheme with that based on the upwind scheme with Roe averaging at the cell interface and non-linear ENO scheme for second-order flux formulas.

  5. Application of the Wire Ablation Dynamics Model to the Design and Optimization of Wire Array Loads of Complex Geometry

    SciTech Connect

    Esaulov, A. A.; Kantsyrev, V. L.; Safronova, A. S.; Williamson, K. M.; Shrestha, I.; Osborne, G. C.

    2009-01-21

    The implosion dynamics of wire array loads of complex geometry, such as nested cylindrical and planar wire arrays, is significantly affected by the uneven current distribution between the array wires, which was considered previously in the Wire Dynamics Model (WDM) simulations. The novel Wire Ablation Dynamics Model (WADM) extends the formalism of the original WDM by including the dynamics of wire ablation. The WADM simulations demonstrate that the implosions of the arrays with higher masses are more ablation dominated. The WADM simulations of the implosions dynamics of nested wire arrays have been performed for the short pulse (100 ns) and long pulse (220 ns) regimes at COBRA generator. Another factor that affects the result of the trade between the ablation and implosion time scales is the form of the current pulse, which can be very different from the classical sine-square shape. The predictions of the array implosion times by the WADM are in very good agreement with the recent experiments at the COBRA and Zebra facilities.

  6. Synergist Ablation as a Rodent Model to Study Satellite Cell Dynamics in Adult Skeletal Muscle.

    PubMed

    Kirby, Tyler J; McCarthy, John J; Peterson, Charlotte A; Fry, Christopher S

    2016-01-01

    In adult skeletal muscles, satellite cells are the primary myogenic stem cells involved in myogenesis. Normally, they remain in a quiescent state until activated by a stimulus, after which they proliferate, differentiate, and fuse into an existing myofiber or form a de novo myofiber. To study satellite cell dynamics in adult murine models, most studies utilize regeneration models in which the muscle is severely damaged and requires the participation from satellite cells in order to repair. Here, we describe a model to study satellite cell behavior in muscle hypertrophy that is independent of muscle regeneration.Synergist ablation surgery involves the surgical removal of the gastrocnemius and soleus muscles resulting in functional overload of the remaining plantaris muscle. This functional overload results in myofiber hypertrophy, as well as the activation, proliferation, and fusion of satellite cells into the myofibers. Within 2 weeks of functional overload, satellite cell content increases approximately 275 %, an increase that is accompanied with a ~60 % increase in the number of myonuclei. Therefore, this can be used as an alternative model to study satellite cell behavior in adulthood that is different from regeneration, and capable of revealing new satellite cell functions in regulating muscle adaptation. PMID:27492164

  7. Synergist Ablation as a Rodent Model to Study Satellite Cell Dynamics in Adult Skeletal Muscle.

    PubMed

    Kirby, Tyler J; McCarthy, John J; Peterson, Charlotte A; Fry, Christopher S

    2016-01-01

    In adult skeletal muscles, satellite cells are the primary myogenic stem cells involved in myogenesis. Normally, they remain in a quiescent state until activated by a stimulus, after which they proliferate, differentiate, and fuse into an existing myofiber or form a de novo myofiber. To study satellite cell dynamics in adult murine models, most studies utilize regeneration models in which the muscle is severely damaged and requires the participation from satellite cells in order to repair. Here, we describe a model to study satellite cell behavior in muscle hypertrophy that is independent of muscle regeneration.Synergist ablation surgery involves the surgical removal of the gastrocnemius and soleus muscles resulting in functional overload of the remaining plantaris muscle. This functional overload results in myofiber hypertrophy, as well as the activation, proliferation, and fusion of satellite cells into the myofibers. Within 2 weeks of functional overload, satellite cell content increases approximately 275 %, an increase that is accompanied with a ~60 % increase in the number of myonuclei. Therefore, this can be used as an alternative model to study satellite cell behavior in adulthood that is different from regeneration, and capable of revealing new satellite cell functions in regulating muscle adaptation.

  8. Mathematical modelling of tumour volume dynamics in response to stereotactic ablative radiotherapy for non-small cell lung cancer

    NASA Astrophysics Data System (ADS)

    Tariq, Imran; Humbert-Vidan, Laia; Chen, Tao; South, Christopher P.; Ezhil, Veni; Kirkby, Norman F.; Jena, Rajesh; Nisbet, Andrew

    2015-05-01

    This paper reports a modelling study of tumour volume dynamics in response to stereotactic ablative radiotherapy (SABR). The main objective was to develop a model that is adequate to describe tumour volume change measured during SABR, and at the same time is not excessively complex as lacking support from clinical data. To this end, various modelling options were explored, and a rigorous statistical method, the Akaike information criterion, was used to help determine a trade-off between model accuracy and complexity. The models were calibrated to the data from 11 non-small cell lung cancer patients treated with SABR. The results showed that it is feasible to model the tumour volume dynamics during SABR, opening up the potential for using such models in a clinical environment in the future.

  9. Coupled molecular dynamics-Monte Carlo model to study the role of chemical processes during laser ablation of polymeric materials

    NASA Astrophysics Data System (ADS)

    Prasad, Manish; Conforti, Patrick F.; Garrison, Barbara J.

    2007-08-01

    The coarse grained chemical reaction model is enhanced to build a molecular dynamics (MD) simulation framework with an embedded Monte Carlo (MC) based reaction scheme. The MC scheme utilizes predetermined reaction chemistry, energetics, and rate kinetics of materials to incorporate chemical reactions occurring in a substrate into the MD simulation. The kinetics information is utilized to set the probabilities for the types of reactions to perform based on radical survival times and reaction rates. Implementing a reaction involves changing the reactants species types which alters their interaction potentials and thus produces the required energy change. We discuss the application of this method to study the initiation of ultraviolet laser ablation in poly(methyl methacrylate). The use of this scheme enables the modeling of all possible photoexcitation pathways in the polymer. It also permits a direct study of the role of thermal, mechanical, and chemical processes that can set off ablation. We demonstrate that the role of laser induced heating, thermomechanical stresses, pressure wave formation and relaxation, and thermochemical decomposition of the polymer substrate can be investigated directly by suitably choosing the potential energy and chemical reaction energy landscape. The results highlight the usefulness of such a modeling approach by showing that various processes in polymer ablation are intricately linked leading to the transformation of the substrate and its ejection. The method, in principle, can be utilized to study systems where chemical reactions are expected to play a dominant role or interact strongly with other physical processes.

  10. Test of Thermal Transport Models through Dynamic Overpressure Stabilization of Ablation-Front Perturbation Growth in Laser-Driven CH Foils

    SciTech Connect

    Gotchev, O.V.; Goncharov, V.N.; Knauer, J.P.; Boehly, T.R.; Collins, T.J.B.; Epstein, R.; Jaanimagi, P.A.; Meyerhofer, D.D.

    2006-03-24

    Heat-flow-induced dynamic overpressure at the perturbed ablation front of an ICF target can stabilize the ablative Richtmyer/Meshkov-like instability and mitigate the subsequent ablative Rayleigh/Taylor (RT) instability. A series of experiments was performed on the OMEGA laser to quantify the dynamic overpressure stabilization during the shock transit. Analysis of the experimental data using hydrocode simulations shows that the observed oscillatory evolution of the ablation-front perturbations depends on Dc, the size of the thermal conduction zone, and the fluid velocity in the blowoff region Vbl that are sensitive to the thermal transport model used. We show that the simulations match the experiment well when the time dependence of the heat-flux inhibition is taken into account using a recently developed nonlocal heat transport model.

  11. Thermal Ablation Modeling for Silicate Materials

    NASA Technical Reports Server (NTRS)

    Chen, Yih-Kanq

    2016-01-01

    A general thermal ablation model for silicates is proposed. The model includes the mass losses through the balance between evaporation and condensation, and through the moving molten layer driven by surface shear force and pressure gradient. This model can be applied in the ablation simulation of the meteoroid and the glassy ablator for spacecraft Thermal Protection Systems. Time-dependent axisymmetric computations are performed by coupling the fluid dynamics code, Data-Parallel Line Relaxation program, with the material response code, Two-dimensional Implicit Thermal Ablation simulation program, to predict the mass lost rates and shape change. The predicted mass loss rates will be compared with available data for model validation, and parametric studies will also be performed for meteoroid earth entry conditions.

  12. Ablation dynamics in coiled wire-array Z-pinches

    SciTech Connect

    Hall, G. N.; Lebedev, S. V.; Suzuki-Vidal, F.; Swadling, G.; Chittenden, J. P.; Bland, S. N.; Harvey-Thompson, A.; Knapp, P. F.; Blesener, I. C.; McBride, R. D.; Chalenski, D. A.; Blesener, K. S.; Greenly, J. B.; Pikuz, S. A.; Shelkovenko, T. A.; Hammer, D. A.; Kusse, B. R.

    2013-02-15

    Experiments to study the ablation dynamics of coiled wire arrays were performed on the MAGPIE generator (1 MA, 240 ns) at Imperial College, and on the COBRA generator at Cornell University's Laboratory of Plasma Studies (1 MA, 100 ns). The MAGPIE generator was used to drive coiled wires in an inverse array configuration to study the distribution of ablated plasma. Using interferometry to study the plasma distribution during the ablation phase, absolute quantitative measurements of electron line density demonstrated very high density contrasts between coiled ablation streams and inter-stream regions many millimetres from the wire. The measured density contrasts for a coiled array were many times greater than that observed for a conventional array with straight wires, indicating that a much greater axial modulation of the ablated plasma may be responsible for the unique implosion dynamics of coiled arrays. Experiments on the COBRA generator were used to study the complex redirection of plasma around a coiled wire that gives rise to the ablation structure exhibited by coiled arrays. Observations of this complex 3D plasma structure were used to validate the current model of coiled array ablation dynamics [Hall et al., Phys. Rev. Lett. 100, 065003 (2008)], demonstrating irrefutably that plasma flow from the wires behaves as predicted. Coiled wires were observed to ablate and implode in the same manner on both machines, indicating that current rise time should not be an issue for the scaling of coiled arrays to larger machines with fast current rise times.

  13. Thermal Ablation Modeling for Silicate Materials

    NASA Technical Reports Server (NTRS)

    Chen, Yih-Kanq

    2016-01-01

    A thermal ablation model for silicates is proposed. The model includes the mass losses through the balance between evaporation and condensation, and through the moving molten layer driven by surface shear force and pressure gradient. This model can be applied in ablation simulations of the meteoroid or glassy Thermal Protection Systems for spacecraft. Time-dependent axi-symmetric computations are performed by coupling the fluid dynamics code, Data-Parallel Line Relaxation program, with the material response code, Two-dimensional Implicit Thermal Ablation simulation program, to predict the mass lost rates and shape change. For model validation, the surface recession of fused amorphous quartz rod is computed, and the recession predictions reasonably agree with available data. The present parametric studies for two groups of meteoroid earth entry conditions indicate that the mass loss through moving molten layer is negligibly small for heat-flux conditions at around 1 MW/cm(exp. 2).

  14. Laser ablation dynamics in metals: The thermal regime

    SciTech Connect

    Mezzapesa, F. P.; Brambilla, M.; Dabbicco, M.; Scamarcio, G.; Columbo, L. L.; Ancona, A.; Sibillano, T.

    2012-07-02

    We studied the laser ablation dynamics of steel in the thermal regime both experimentally and theoretically. The real-time monitoring of the process shows that the ablation rate depends on laser energy density and ambient pressure during the exposure time. We demonstrated that the ablation efficiency can be enhanced when the pressure is reduced with respect to the atmospheric pressure for a given laser fluence, reaching an upper limit despite of high-vacuum conditions. An analytical model based on the Hertz-Knudsen law reproduces all the experimental results.

  15. Rare event molecular dynamics simulations of plasma induced surface ablation

    SciTech Connect

    Sharia, Onise; Holzgrafe, Jeffrey; Park, Nayoung; Henkelman, Graeme

    2014-08-21

    The interaction of thermal Ar plasma particles with Si and W surfaces is modeled using classical molecular dynamics (MD) simulations. At plasma energies above the threshold for ablation, the ablation yield can be calculated directly from MD. For plasma energies below threshold, the ablation yield becomes exponentially low, and direct MD simulations are inefficient. Instead, we propose an integration method where the yield is calculated as a function of the Ar incident kinetic energy. Subsequent integration with a Boltzmann distribution at the temperature of interest gives the thermal ablation yield. At low plasma temperatures, the ablation yield follows an Arrhenius form in which the activation energy is shown to be the threshold energy for ablation. Interestingly, equilibrium material properties, including the surface and bulk cohesive energy, are not good predictors of the threshold energy for ablation. The surface vacancy formation energy is better, but is still not a quantitative predictor. An analysis of the trajectories near threshold shows that ablation occurs by different mechanisms on different material surfaces, and both the mechanism and the binding of surface atoms determine the threshold energy.

  16. Rare event molecular dynamics simulations of plasma induced surface ablation.

    PubMed

    Sharia, Onise; Holzgrafe, Jeffrey; Park, Nayoung; Henkelman, Graeme

    2014-08-21

    The interaction of thermal Ar plasma particles with Si and W surfaces is modeled using classical molecular dynamics (MD) simulations. At plasma energies above the threshold for ablation, the ablation yield can be calculated directly from MD. For plasma energies below threshold, the ablation yield becomes exponentially low, and direct MD simulations are inefficient. Instead, we propose an integration method where the yield is calculated as a function of the Ar incident kinetic energy. Subsequent integration with a Boltzmann distribution at the temperature of interest gives the thermal ablation yield. At low plasma temperatures, the ablation yield follows an Arrhenius form in which the activation energy is shown to be the threshold energy for ablation. Interestingly, equilibrium material properties, including the surface and bulk cohesive energy, are not good predictors of the threshold energy for ablation. The surface vacancy formation energy is better, but is still not a quantitative predictor. An analysis of the trajectories near threshold shows that ablation occurs by different mechanisms on different material surfaces, and both the mechanism and the binding of surface atoms determine the threshold energy. PMID:25149805

  17. Dynamics of mid-infrared femtosecond laser resonant ablation

    NASA Astrophysics Data System (ADS)

    Pang, Dongqing; Li, Yunxuan; Wang, Qingyue

    2014-06-01

    Resonant ablation is beneficial to avoiding uncontrollable subsurface damages in the laser ablation of polymers. In this paper the dynamics of mid-infrared laser resonant ablation of polylactic acid and toluene was calculated by using fluid dynamic equations. The merits and drawbacks of mid-infrared femtosecond laser resonant ablation of high molecular weight polymers have been discussed.

  18. Theoretical Modeling for Hepatic Microwave Ablation

    PubMed Central

    Prakash, Punit

    2010-01-01

    Thermal tissue ablation is an interventional procedure increasingly being used for treatment of diverse medical conditions. Microwave ablation is emerging as an attractive modality for thermal therapy of large soft tissue targets in short periods of time, making it particularly suitable for ablation of hepatic and other tumors. Theoretical models of the ablation process are a powerful tool for predicting the temperature profile in tissue and resultant tissue damage created by ablation devices. These models play an important role in the design and optimization of devices for microwave tissue ablation. Furthermore, they are a useful tool for exploring and planning treatment delivery strategies. This review describes the status of theoretical models developed for microwave tissue ablation. It also reviews current challenges, research trends and progress towards development of accurate models for high temperature microwave tissue ablation. PMID:20309393

  19. Laser ablation plume dynamics in nanoparticle synthesis

    SciTech Connect

    Osipov, V V; Platonov, V V; Lisenkov, V V

    2009-06-30

    The dynamics of the plume ejected from the surface of solid targets (YSZ, Nd:YAG and graphite) by a CO{sub 2} laser pulse with a duration of {approx}500 {mu}s (at the 0.03 level), energy of 1.0-1.3 J and peak power of 6-7 kW have been studied using high-speed photography of the plume luminescence and shadow. The targets were used to produce nanopowders by laser evaporation. About 200 {mu}s after termination of the pulse, shadowgraph images of the plumes above the YSZ and Nd:YAG targets showed dark straight tracks produced by large particles. The formation of large ({approx}10 {mu}m) particles is tentatively attributed to cracking of the solidified melt at the bottom of the ablation crater. This is supported by the fact that no large particles are ejected from graphite, which sublimes without melting. Further support to this hypothesis is provided by numerical 3D modelling of melt cooling in craters produced by laser pulses of different shapes. (interaction of laser radiation with matter. laser plasma)

  20. Dynamics of tissue shrinkage during ablative temperature exposures

    PubMed Central

    Rossmann, Christian; Garrett-Mayer, Elizabeth; Rattay, Frank; Haemmerich, Dieter

    2014-01-01

    There is a lack of studies that examine dynamics of heat-induced shrinkage of organ tissues. Clinical procedures such as radiofrequency ablation, microwave ablation or high-intensity focused ultrasound, use heat to treat diseases such as cancer and cardiac arrhythmia. When heat is applied to tissues, shrinkage occurs due to protein denaturation, dehydration, and contraction of collagen at temperatures greater 50ºC. This is particularly relevant for image-guided procedures such as tumor ablation, where pre- and post-treatment images are compared and any changes in dimensions must be considered to avoid misinterpretations of the treatment outcome. We present data from ex vivo, isothermal shrinkage tests in porcine liver tissue, where axial changes in tissue length were recorded during 15 minutes of heating to temperatures between 60 and 95ºC. A mathematical model was developed to accurately describe the time and temperature-dependent shrinkage behavior. Shrinkage dynamics had same characteristics independent of temperature; the estimated relative shrinkage, adjusted for time since death, after 15 min heating to temperatures of 60, 65, 75, 85 and 95ºC, was 12.3, 13.8, 16.6, 19.2, and 21.7%, respectively. Our results demonstrate shrinkage dynamics of organ tissues, and suggest the importance of considering tissue shrinkage for thermal ablative treatments. PMID:24345880

  1. Laser-solid interaction and dynamics of laser-ablated materials

    SciTech Connect

    Chen, K.R.; Neboeuf, J.N.; Wood, R.F.; Geohegan, D.B.; Donato, J.M.; Liu, C.L.; Puretzky, A.A.

    1995-09-01

    An annealing model is extended to treat the vaporization process, and a hydrodynamic model describes the ablated material. We find that dynamic source and ionization effects accelerate the expansion front of the ablated plume with thermal vaporization temperature. The vaporization process and plume propagation in high background gas pressure are studied.

  2. The effect of initial and dynamic liver conditions on RF ablation size: a study in perfused and non-perfused animal models

    NASA Astrophysics Data System (ADS)

    Belous, Anna; Podhajsky, Ronald J.

    2009-02-01

    Investigators reporting RF ablation (RFA) studies often use different initial and dynamic conditions, often in porcine or bovine liver models. This study examines the effects of initial temperature, prior freezing, and perfusion in these models. Understanding how these variables affect RFA size provides some basis for comparing data from different studies. We obtained porcine and bovine livers from a slaughterhouse and divided them into experimental groups each with discrete initial temperatures set in the range of 12 to 37°C. The livers were used either the day of harvest or frozen within 1-3 days prior to RFA treatment. A perfused liver model was developed to simulate human blood flow rates and allowed accurate control of the temperature and flow rate. Saline (0.9%) was substituted for blood. The non-perfused liver model group included bovine and porcine tissue; whereas the perfused liver model group included only porcine tissue. One experiment included porcine livers that were perfused at different flow rates and with different saline concentrations. Harvested tissue from this group was examined under a light microscope and the level of edema was assessed using image processing software. The results demonstrate no significant difference in RF lesion sizes between porcine and bovine livers. Freezing the tissue prior to treatment has no significant effect but the initial temperature does significantly affect the size of ablation. The ablation size in perfused liver is similar to in vivo results (earlier study) but is significantly smaller then non-perfused liver. Morphological analysis indicates that perfusion, freezing, and saline concentration cause significant tissue edema.

  3. On dynamic gas ablation from spherical galaxies

    NASA Astrophysics Data System (ADS)

    Nepveu, M.

    1981-05-01

    Two-dimensional, time dependent gas dynamic calculations are presented on the transonic motion of galaxies through a cluster medium. Lea and De Young's (1976) calculations are extended to include violent behavior in the center. On time scales of 10 to the 8th yr, galaxies in clusters can already lose a significant fraction of their gaseous content (up to 50% has been found in the calculations). This dynamic ablation occurs through rarefaction rather than shock heating. Explosions in spherical galaxies become effective as mechanisms for gas removal only if the galaxy moves with respect to its surroundings. Speculations are made on stripping of spiral galaxies (moving head-on in a cluster); the Gunn and Gott (1972) stripping formula is put to doubt. A method is suggested to obtain information on the state of motion of field galaxies.

  4. On the Ablation Models of Fuel Pellets

    SciTech Connect

    Rozhansky, V.A.; Senichenkov, I.Yu.

    2005-12-15

    The neutral gas shielding model and neutral-gas-plasma shielding model are analyzed qualitatively. The main physical processes that govern the formation of the shielding gas cloud and, consequently, the ablation rate are considered. For the neutral gas shielding model, simple formulas relating the ablation rate and cloud parameters to the parameters of the pellet and the background plasma are presented. The estimates of the efficiency of neutral gas shielding and plasma shielding are compared. It is shown that the main portion of the energy flux of the background electrons is released in the plasma cloud. Formulas for the ablation rate and plasma parameters are derived in the neutral-gas-plasma shielding model. The question is discussed as to why the neutral gas shielding model describes well the ablation rate of the pellet material, although it does not take into account the ionization effects and the effects associated with the interaction of ionized particles with the magnetic field. The reason is that the ablation rate depends weakly on the energy flux of hot electrons; as a result, the attenuation of this flux by the electrostatic shielding and plasma shielding has little effect on the ablation rate. This justifies the use of the neutral gas shielding model to estimate the ablation rate (to within a factor of about 2) over a wide range of parameters of the pellet and the background plasma.

  5. Simple spherical ablative-implosion model

    SciTech Connect

    Mayer, F.J.; Steele, J.T.; Larsen, J.T.

    1980-06-23

    A simple model of the ablative implosion of a high-aspect-ratio (shell radius to shell thickness ratio) spherical shell is described. The model is similar in spirit to Rosenbluth's snowplow model. The scaling of the implosion time was determined in terms of the ablation pressure and the shell parameters such as diameter, wall thickness, and shell density, and compared these to complete hydrodynamic code calculations. The energy transfer efficiency from ablation pressure to shell implosion kinetic energy was examined and found to be very efficient. It may be possible to attach a simple heat-transport calculation to our implosion model to describe the laser-driven ablation-implosion process. The model may be useful for determining other energy driven (e.g., ion beam) implosion scaling.

  6. Optical modeling of laser ablated microstructures

    NASA Astrophysics Data System (ADS)

    Gower, M. C.; Davies, E.; Holmes, A. S.

    2012-11-01

    From only an a priori knowledge of the optical parameters of a laser beam, the delivery system together with a substrate's material properties, a ray-tracing model capable of predicting the 3-D topology of micro/nanostructures machined by pulsed laser ablation has been developed. The model includes secondary illumination effects produced by the microstructure created by successive pulses (wall reflections, refraction, wave guiding, shadowing, etc.) as well as the complete optical properties of the beam delivery system. We have used material ablation by pulsed excimer lasers and associated beam delivery systems to demonstrate some of the capabilities of the model. Good agreement is obtained between computations and experimental results in terms of the predicted ablation depth per pulse and the wall taper angle of channels and holes. The model can predict ablated profiles of holes and indicate the most efficient drilling strategy in terms of material removal rates. The model also shows diffraction effects are not required to explain the tapering vertical walls observed when ablating microstructures. Finally, the model has been used to demonstrate aberrations in an optical imaging system limiting the creation of submicron features in an ablated microstructure. Provided photons are absorbed linearly in a substrate according to Beer's law with negligible thermal diffusion effects, the model is equally applicable to using other types of pulsed laser sources and systems with imaged or focused beams.

  7. Higher Order Chemistry Models in the CFD Simulation of Laser-Ablated Carbon Plumes

    NASA Technical Reports Server (NTRS)

    Greendyke, R. B.; Creel, J. R.; Payne, B. T.; Scott, C. D.

    2005-01-01

    Production of single-walled carbon nanotubes (SWNT) has taken place for a number of years and by a variety of methods such as laser ablation, chemical vapor deposition, and arc-jet ablation. Yet, little is actually understood about the exact chemical kinetics and processes that occur in SWNT formation. In recent time, NASA Johnson Space Center has devoted a considerable effort to the experimental evaluation of the laser ablation production process for SWNT originally developed at Rice University. To fully understand the nature of the laser ablation process it is necessary to understand the development of the carbon plume dynamics within the laser ablation oven. The present work is a continuation of previous studies into the efforts to model plume dynamics using computational fluid dynamics (CFD). The ultimate goal of the work is to improve understanding of the laser ablation process, and through that improved understanding, refine the laser ablation production of SWNT.

  8. Principles of the radiative ablation modeling

    NASA Astrophysics Data System (ADS)

    Saillard, Yves; Arnault, Philippe; Silvert, Virginie

    2010-12-01

    Indirectly driven inertial confinement fusion (ICF) rests on the setting up of a radiation temperature within a laser cavity and on the optimization of the capsule implosion ablated by this radiation. In both circumstances, the ablation of an optically thick medium is at work. The nonlinear radiation conduction equations that describe this phenomenon admit different kinds of solutions called generically Marshak waves. In this paper, a completely analytic model is proposed to describe the ablation in the subsonic regime relevant to ICF experiments. This model approximates the flow by a deflagrationlike structure where Hugoniot relations are used in the stationary part from the ablation front up to the isothermal sonic Chapman-Jouguet point and where the unstationary expansion from the sonic point up to the external boundary is assumed quasi-isothermal. It uses power law matter properties. It can also accommodate arbitrary boundary conditions provided the ablation wave stays very subsonic and the surface temperature does not vary too quickly. These requirements are often met in realistic situations. Interestingly, the ablated mass rate, the ablation pressure, and the absorbed radiative energy depend on the time history of the surface temperature, not only on the instantaneous temperature values. The results compare very well with self-similar solutions and with numerical simulations obtained by hydrodynamic code. This analytic model gives insight into the physical processes involved in the ablation and is helpful for optimization and sensitivity studies in many situations of interest: radiation temperature within a laser cavity, acceleration of finite size medium, and ICF capsule implosion, for instance.

  9. Principles of the radiative ablation modeling

    SciTech Connect

    Saillard, Yves; Arnault, Philippe; Silvert, Virginie

    2010-12-15

    Indirectly driven inertial confinement fusion (ICF) rests on the setting up of a radiation temperature within a laser cavity and on the optimization of the capsule implosion ablated by this radiation. In both circumstances, the ablation of an optically thick medium is at work. The nonlinear radiation conduction equations that describe this phenomenon admit different kinds of solutions called generically Marshak waves. In this paper, a completely analytic model is proposed to describe the ablation in the subsonic regime relevant to ICF experiments. This model approximates the flow by a deflagrationlike structure where Hugoniot relations are used in the stationary part from the ablation front up to the isothermal sonic Chapman-Jouguet point and where the unstationary expansion from the sonic point up to the external boundary is assumed quasi-isothermal. It uses power law matter properties. It can also accommodate arbitrary boundary conditions provided the ablation wave stays very subsonic and the surface temperature does not vary too quickly. These requirements are often met in realistic situations. Interestingly, the ablated mass rate, the ablation pressure, and the absorbed radiative energy depend on the time history of the surface temperature, not only on the instantaneous temperature values. The results compare very well with self-similar solutions and with numerical simulations obtained by hydrodynamic code. This analytic model gives insight into the physical processes involved in the ablation and is helpful for optimization and sensitivity studies in many situations of interest: radiation temperature within a laser cavity, acceleration of finite size medium, and ICF capsule implosion, for instance.

  10. Microwave Ablation Compared with Radiofrequency Ablation for Breast Tissue in an Ex Vivo Bovine Udder Model

    SciTech Connect

    Tanaka, Toshihiro; Westphal, Saskia; Isfort, Peter; Braunschweig, Till; Penzkofer, Tobias Bruners, Philipp; Kichikawa, Kimihiko; Schmitz-Rode, Thomas Mahnken, Andreas H.

    2012-08-15

    Purpose: To compare the effectiveness of microwave (MW) ablation with radiofrequency (RF) ablation for treating breast tissue in a nonperfused ex vivo model of healthy bovine udder tissue. Materials and Methods: MW ablations were performed at power outputs of 25W, 35W, and 45W using a 915-MHz frequency generator and a 2-cm active tip antenna. RF ablations were performed with a bipolar RF system with 2- and 3-cm active tip electrodes. Tissue temperatures were continuously monitored during ablation. Results: The mean short-axis diameters of the coagulation zones were 1.34 {+-} 0.14, 1.45 {+-} 0.13, and 1.74 {+-} 0.11 cm for MW ablation at outputs of 25W, 35W, and 45W. For RF ablation, the corresponding values were 1.16 {+-} 0.09 and 1.26 {+-} 0.14 cm with electrodes having 2- and 3-cm active tips, respectively. The mean coagulation volumes were 2.27 {+-} 0.65, 2.85 {+-} 0.72, and 4.45 {+-} 0.47 cm{sup 3} for MW ablation at outputs of 25W, 35W, and 45W and 1.18 {+-} 0.30 and 2.29 {+-} 0.55 cm{sup 3} got RF ablation with 2- and 3-cm electrodes, respectively. MW ablations at 35W and 45W achieved significantly longer short-axis diameters than RF ablations (P < 0.05). The highest tissue temperature was achieved with MW ablation at 45W (P < 0.05). On histological examination, the extent of the ablation zone in MW ablations was less affected by tissue heterogeneity than that in RF ablations. Conclusion: MW ablation appears to be advantageous with respect to the volume of ablation and the shape of the margin of necrosis compared with RF ablation in an ex vivo bovine udder.

  11. Numerical Modeling of Ablation Heat Transfer

    NASA Technical Reports Server (NTRS)

    Ewing, Mark E.; Laker, Travis S.; Walker, David T.

    2013-01-01

    A unique numerical method has been developed for solving one-dimensional ablation heat transfer problems. This paper provides a comprehensive description of the method, along with detailed derivations of the governing equations. This methodology supports solutions for traditional ablation modeling including such effects as heat transfer, material decomposition, pyrolysis gas permeation and heat exchange, and thermochemical surface erosion. The numerical scheme utilizes a control-volume approach with a variable grid to account for surface movement. This method directly supports implementation of nontraditional models such as material swelling and mechanical erosion, extending capabilities for modeling complex ablation phenomena. Verifications of the numerical implementation are provided using analytical solutions, code comparisons, and the method of manufactured solutions. These verifications are used to demonstrate solution accuracy and proper error convergence rates. A simple demonstration of a mechanical erosion (spallation) model is also provided to illustrate the unique capabilities of the method.

  12. Dynamics of Laser Ablation in Superfluid ^4He

    NASA Astrophysics Data System (ADS)

    Buelna, X.; Popov, E.; Eloranta, J.

    2016-10-01

    Pulsed laser ablation of metal targets immersed in superfluid ^4He is visualized by time-resolved shadowgraph photography and the products are analyzed by post-experiment atomic force microscopy (AFM) measurements. The expansion dynamics of the gaseous ablation half-bubble on the target surface appears underdamped and follows the predicted behavior for the thermally induced bubble growth mechanism. An inherent instability of the ablation bubble appears near its maximum radius and no tightly focused cavity collapse or rebound events are observed. During the ablation bubble retreat phase, the presence of sharp edges in the target introduces flow patterns that lead to the creation of large classical vortex rings. Furthermore, on the nanometer scale, AFM data reveal that the metal nanoparticles created by laser ablation are trapped in spherical vortex tangles and quantized vortex rings present in the non-equilibrium liquid.

  13. Diagnosing Implosion Velocity and Ablator Dynamics at NIF

    NASA Astrophysics Data System (ADS)

    Grim, Gary; Hayes, Anna; Jungman, Jerry; Wilson, Doug; Wilhelmy, Jerry; Bradley, Paul; Rundberg, Bob; Cerjan, Charlie

    2009-10-01

    An enhanced understanding of the environment in a burning NIF capsule is of interest to both astrophysics and thermonuclear ignition. In this talk we introduce a new diagnostic idea, designed to measure dynamic aspects of the capsule implosion that are not currently accessible. During the burn,the NIF capsule ablator is moving relative to the 14.1 MeV dt neutrons that are traversing the capsule. The resulting neutron-ablator Doppler shift causes a few unique nuclear reactions to become sensitive detectors of the ablator velocity at peak burn time. The ``point-design'' capsule at the NIF will be based on a ^9Be ablator, and the ^9Be(n,p)^9Li reaction has an energy threshold of 14.2 MeV, making it the ideal probe. As discussed in detail below, differences in the ablator velocity lead to significant differences in the rate of ^9Li production. We present techniques for measuring this ^9Li implosion velocity diagnostic at the NIF. The same experimental techniques, measuring neutron reactions on the ablator material, will allow us to determine other important dynamical quantities, such as the areal density and approximate thickness of the ablator at peak burn.

  14. General Model for Multicomponent Ablation Thermochemistry

    NASA Technical Reports Server (NTRS)

    Milos, Frank S.; Marschall, Jochen; Rasky, Daniel J. (Technical Monitor)

    1994-01-01

    A previous paper (AIAA 94-2042) presented equations and numerical procedures for modeling the thermochemical ablation and pyrolysis of thermal protection materials which contain multiple surface species. This work describes modifications and enhancements to the Multicomponent Ablation Thermochemistry (MAT) theory and code for application to the general case which includes surface area constraints, rate limited surface reactions, and non-thermochemical mass loss (failure). Detailed results and comparisons with data are presented for the Shuttle Orbiter reinforced carbon-carbon oxidation protection system which contains a mixture of sodium silicate (Na2SiO3), silica (SiO2), silicon carbide (SiC), and carbon (C).

  15. Microscopic and macroscopic modeling of femtosecond laser ablation of metals

    NASA Astrophysics Data System (ADS)

    Povarnitsyn, Mikhail E.; Fokin, Vladimir B.; Levashov, Pavel R.

    2015-12-01

    Simulation of femtosecond laser ablation of a bulk aluminum target is performed using two complementary approaches. The first method is single-fluid two-temperature hydrodynamics (HD) completed with a two-temperature equation of state (EOS). The second approach is a combination of classical molecular dynamics (MD) and a continuum model of a free electron subsystem. In both methods, an identical and accurate description of optical and transport properties of the electron subsystem is based on wide-range models reproducing effects of electron heat wave propagation, electron-phonon/ion coupling and laser energy absorption on a time-dependent profile of the dielectric function. For simulation of homogeneous nucleation in a metastable liquid phase, a kinetic model of nucleation is implemented in the HD approach. The phase diagrams of the EOS and MD potential are in good agreement that gives opportunity to compare the dynamics of laser ablation obtained by both methods directly. Results of simulation are presented in the range of incident fluences 0.1-20 J/cm2 and match well with experimental findings for an ablation crater depth. The MD accurately reproduces nonequilibrium phase transitions and takes into account surface effects on nanoscale. The HD approach demonstrates good qualitative agreement with the MD method in the dynamics of phase explosion and spallation. Other advantages and disadvantages of both approaches are examined and discussed.

  16. Diagnosing implosion velocity and ablator dynamics at NIF (u)

    SciTech Connect

    Hayes, Anna; Grim, Gary; Jungnam, Jerry; Bradley, Paul; Rundberg, Bob; Wilhelmy, Jerry; Wilson, Doug

    2009-07-09

    An enhanced understanding of the unique physics probed in a burning NIP capsule is important for both nuclear weapons physics and thermonuclear ignition. In this talk we introduce a new diagnostic idea, designed to measure dynamic aspects of the capsule implosion that are not currently accessible. The current set of diagnostics for the NIF experiments includes reaction history (a time resolved measure of the d + t burn), neutron time-of-flight and spectrometry and spatial imaging of the neutron production and scattering. Although valuable, this abbreviated set of diagnostics cannot determine key dynamical properties of the implosion, such as implosion velocity (v{sub impl}) and ablator thickness. To surpass the present limits of {approx} 10{sup 15} d+t reactions, it will be necessary to increase significantly the implosion energy delivered to the DT fuel by finely tuning the balance between the remaining (imploding) ablator mass and velocity. If too much mass remains, the implosion velocity will be too slow, and the subsecpwnt PdV work will not be sufficient to overcome cooling via conduction and radiation. If too little mass remains, hydrodynamic instabilities will occur, resulting in unpredictable and degraded performance. Detailed calculations suggest the ablator must reach an implosion velocity of 3-4 x 10{sup 7} cm/sec and an areal density of {rho}{Delta}R {approx}200 mg/cm{sup 2} in order to achieve ignition. The authors present a new scheme to measure these important quantities using neutron reactions on the ablator material. During the burn, the ablator is moving relative to the 14.1 MeV d+t neutrons that are traversing the capsule. The resulting neutron-ablator Doppler shift causes a few unique nuclear reactions to become sensitive detectors of the ablator velocity at peak burn time. The 'point-design' capsule at the NIF will be based on a {sup 9}Be ablator, and the {sup 9}Be(n,p){sup 9}Li reaction has an energy threshold of 14.2 MeV, making it the ideal

  17. Photochemical processes in laser ablation of organic solids: Molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Yingling, Yaroslava G.

    In this thesis, a comprehensive study of the effect of the photochemical processes on laser ablation mechanisms has been conducted using molecular dynamics simulations. We developed a new concept for modeling photochemical processes in laser ablation of organic films using a mesoscopic coarse-grain breathing sphere model for molecular dynamics simulations. The main advantage of our model is the ability to study the dynamics of the system at the mesoscopic length scale, a regime that is not accessible either with atomistic or continuum computational methods. The photodecomposition of the excited molecules and the chemical reaction patterns in our simulations are based on the photochemistry of chlorobenzene due to ease of its fragmentation and available experimental data. Interpretation of the experimental data is the main objective of our theoretical efforts. Molecular dynamics simulations are used to investigate the effect of photochemical processes on molecular ejection mechanisms in 248-nm laser irradiation of organic solids. Photochemical reactions are found to release additional energy into the irradiated sample and decrease the average cohesive energy, therefore decreasing the value of the ablation threshold. The yield of emitted fragments becomes significant only above the ablation threshold. Below the ablation threshold, only the most volatile photoproduct, HCl, is ejected in very small amounts, whereas the remainder of photoproducts are trapped inside the sample. The presence of photochemical decomposition processes and subsequent chemical reactions changes the temporal and spatial energy deposition profile from pure photothermal ablation. The chemical reactions create an additional local pressure build up and, as a result, generate a strong and broad acoustic pressure wave propagating toward the bottom of the computational cell. The strong pressure wave in conjunction with the temperature increase in the absorbing region causes the ejection of hot massive

  18. Efficiency and Plume Dynamics for Mid-IR Laser Ablation of Cornea

    NASA Astrophysics Data System (ADS)

    Jayasinghe, Aroshan; Ivanov, Borislav; Hutson, M. Shane

    2009-03-01

    This paper reports ablation experiments on porcine corneal tissue using the Vanderbilt Mark III Free Electron Laser (FEL) and a tabletop Raman-shifted Alexandrite laser. These experiments were designed to test previous models that suggested wavelength and intensity dependent ablation mechanisms. In one test, we compare ablation efficiency and plume dynamics for two FEL wavelengths (λ=2.77, 6.45 μm) chosen such that different components of the tissue matrix act as the primary chromophore (water or protein respectively), while keeping the total absorption constant. We find small differences in ablation efficiency (with slightly more efficient ablation at 2.77 μm); no difference in shockwave propagation; and slightly more particulate matter in the plume at 6.45 μm. In a second test, we find that the Raman-shifted Alexandrite laser has similar ablation efficiency to the FEL in the 6-7 μm range -- despite a ˜500-fold higher intensity. Although these results do not confirm the previous model predictions, the findings do suggest that the Raman-shifted laser can be a viable alternative to the FEL for surgical applications.

  19. Modeling CO{sub 2} Laser Ablative Impulse with Polymers

    SciTech Connect

    Sinko, John E.; Phipps, Claude R.; Sasoh, Akihiro

    2010-10-08

    Laser ablation vaporization models have usually ignored the spatial dependence of the laser beam. Here, we consider effects from modeling using a Gaussian beam for both photochemical and photothermal conditions. The modeling results are compared to experimental and literature data for CO{sub 2} laser ablation of the polymer polyoxymethylene under vacuum, and discussed in terms of the ablated mass areal density and momentum coupling coefficient. Extending the scope of discussion, laser ablative impulse generation research has lacked a cohesive strategy for linking the vaporization and plasma regimes. Existing models, mostly formulated for ultraviolet laser systems or metal targets, appear to be inappropriate or impractical for applications requiring CO{sub 2} laser ablation of polymers. A recently proposed method for linking the vaporization and plasma regimes for analytical modeling is addressed here along with the implications of its use. Key control parameters are considered, along with the major propulsion parameters needed for laser ablation propulsion modeling.

  20. Integration of natural data within a numerical model of ablative subduction: A possible interpretation for the Alpine dynamics of the Austroalpine crust.

    NASA Astrophysics Data System (ADS)

    Roda, M.; Spalla, M. I.; Marotta, A. M.

    2012-04-01

    A numerical modelling approach is used to validate the physical and geological reliability of the ablative subduction mechanism during Alpine convergence in order to interpret the tectonic and metamorphic evolution of an inner portion of the Alpine belt: the Austroalpine Domain. The model predictions and the natural data for the Austroalpine of the Western Alps agree very well in terms of P-T peak conditions, relative chronology of peak and exhumation events, P-T-t paths, thermal gradients and the tectonic evolution of the continental rocks. These findings suggest that a pre-collisional evolution of this domain, with the burial of the continental rocks (induced by ablative subduction of the overriding Adria plate) and their exhumation (driven by an upwelling flow generated in a hydrated mantle wedge) could be a valid mechanism that reproduces the actual tectono-metamorphic configuration of this part of the Alps. There is less agreement between the model predictions and the natural data for the Austroalpine of the Central-Eastern Alps. Based on the natural data available in the literature, a critical discussion of the other proposed mechanisms is presented, and additional geological factors that should be considered within the numerical model are suggested to improve the fitting to the numerical results; these factors include variations in the continental and/or oceanic thickness, variation of the subduction rate and/or slab dip, the initial thermal state of the passive margin, the occurrence of continental collision and an oblique convergence.

  1. Mathematical Modeling of Laser Ablation in Liquids with Applications to Laser Ultrasonics

    SciTech Connect

    Conant, R. J.; Telschow, Kenneth Louis; Walter, John Bradley

    2002-12-01

    The use of laser ablation as a means of generating ultrasonic waves in liquid metals is studied in this paper. A mathematical model for predicting the onset of ablation is developed, as is a model of the ablation process based on steady state, one-dimensional gas dynamics in which the vapor phase is treated as an ideal gas. The results of this model are then used in a quasi-two-dimensional model of laser ablation that accounts for the spatial distribution of intensity in the laser beam. Model predictions are compared with experiments conducted on liquid mercury and excellent agreement is obtained. Based on these results, a simplified model is developed that shows excellent agreement with both the theory and the experiments.

  2. Conditional Lineage Ablation to Model Human Diseases

    NASA Astrophysics Data System (ADS)

    Lee, Paul; Morley, Gregory; Huang, Qian; Fischer, Avi; Seiler, Stephanie; Horner, James W.; Factor, Stephen; Vaidya, Dhananjay; Jalife, Jose; Fishman, Glenn I.

    1998-09-01

    Cell loss contributes to the pathogenesis of many inherited and acquired human diseases. We have developed a system to conditionally ablate cells of any lineage and developmental stage in the mouse by regulated expression of the diphtheria toxin A (DTA) gene by using tetracycline-responsive promoters. As an example of this approach, we targeted expression of DTA to the hearts of adult mice to model structural abnormalities commonly observed in human cardiomyopathies. Induction of DTA expression resulted in cell loss, fibrosis, and chamber dilatation. As in many human cardiomyopathies, transgenic mice developed spontaneous arrhythmias in vivo, and programmed electrical stimulation of isolated-perfused transgenic hearts demonstrated a strikingly high incidence of spontaneous and inducible ventricular tachycardia. Affected mice showed marked perturbations of cardiac gap junction channel expression and localization, including a subset with disorganized epicardial activation patterns as revealed by optical action potential mapping. These studies provide important insights into mechanisms of arrhythmogenesis and suggest that conditional lineage ablation may have wide applicability for studies of disease pathogenesis.

  3. Damage in materials following ablation by ultrashort laser pulses: A molecular-dynamics study

    SciTech Connect

    Bouilly, Delphine; Perez, Danny; Lewis, Laurent J.

    2007-11-01

    The formation of craters following femtosecond- and picosecond-pulse laser ablation in the thermal regime is studied using a generic two-dimensional numerical model based on molecular-dynamics simulations and the Lennard-Jones potential. Femtosecond pulses are found to produce very clean craters through a combination of etching of the walls and the formation of a very thin heat affected zone. Our simulations also indicate that dislocations are emitted continuously during all of the ablation process (i.e., for hundreds of ps). For picosecond pulses, we observe much thicker heat affected zones which result from melting and recrystallization following the absorption of the light. In this case also, continuous emission of dislocations--though fewer in number--takes place throughout the ablation process.

  4. Comparisons of kinetic ablation models for the capillary discharge

    SciTech Connect

    Li Rui; Li Xingwen; Jia Shenli; Murphy, Anthony B.

    2010-07-15

    The properties of kinetic ablation models are considered in this paper. The widely used kinetic ablation model (model-K) only considers monatomic vapor. A revised model (model-Z) was introduced by taking into account the polyatomic vapor's internal degrees of freedom, as well as the temperature dependence of the average particle mass. In this work, both temperature and pressure dependence of average particle mass and the specific heat ratio {gamma} are taken into account, producing an improved version of model-Z (denoted model-Z{sup *}). Ablation data calculated by model-K and model-Z* for two typical capillary materials are presented. Compared to model-K, model-Z* predicts an increased ablation rate at lower plasma temperature and higher plasma density, and a decreased rate for the opposite conditions. Finally, based on the plasma parameters in a typical discharge cycle, all three models are used to calculate the time-dependent ablation rate and the integrated ablated mass. It is found that the main difference between their results arises because of the different average particle masses near the wall surface, and model-Z* is the most accurate for the discharge cycle considered. Further, it is found that the ablation parameters are highly sensitive to the pressure, in particular, through the pressure dependence of average particle mass.

  5. Laser-solid interaction and dynamics of the laser-ablated materials

    SciTech Connect

    Chen, K.R.; Leboeuf, J.N.; Geohegan, D.B.; Wood, R.F.; Donato, J.M.; Liu, C.L.; Puretzky, A.A.

    1995-07-01

    Rapid transformations through the liquid and vapor phases induced by laser-solid interactions are described by the authors` thermal model with the Clausius-Clapeyron equation to determine the vaporization temperature under different surface pressure condition. Hydrodynamic behavior of the vapor during and after ablation is described by gas dynamic equations. These two models are coupled. Modeling results show that lower background pressure results lower laser energy density threshold for vaporization. The ablation rate and the amount of materials removed are proportional to the laser energy density above its threshold. The authors also demonstrate a dynamic source effect that accelerates the unsteady expansion of laser-ablated material in the direction perpendicular to the solid. A dynamic partial ionization effect is studied as well. A self-similar theory shows that the maximum expansion velocity is proportional to c{sub s}{alpha}, where 1 {minus} {alpha} is the slope of the velocity profile. Numerical hydrodynamic modeling is in good agreement with the theory. With these effects, {alpha} is reduced. Therefore, the expansion front velocity is significantly higher than that from conventional models. The results are consistent with experiments. They further study how the plume propagates in high background gas condition. Under appropriate conditions, the plume is slowed down, separates with the background, is backward moving, and hits the solid surface. Then, it splits into two parts when it rebounds from the surface. The results from the modeling will be compared with experimental observations where possible.

  6. Computational modeling of ultra-short-pulse ablation of enamel

    SciTech Connect

    London, R.A.; Bailey, D.S.; Young, D.A.

    1996-02-29

    A computational model for the ablation of tooth enamel by ultra-short laser pulses is presented. The role of simulations using this model in designing and understanding laser drilling systems is discussed. Pulses of duration 300 sec and intensity greater than 10{sup 12} W/cm{sup 2} are considered. Laser absorption proceeds via multi-photon initiated plasma mechanism. The hydrodynamic response is calculated with a finite difference method, using an equation of state constructed from thermodynamic functions including electronic, ion motion, and chemical binding terms. Results for the ablation efficiency are presented. An analytic model describing the ablation threshold and ablation depth is presented. Thermal coupling to the remaining tissue and long-time thermal conduction are calculated. Simulation results are compared to experimental measurements of the ablation efficiency. Desired improvements in the model are presented.

  7. Energy transport analysis in ultrashort pulse laser ablation through combined molecular dynamics and Monte Carlo simulation

    SciTech Connect

    Hu Wenqian; Shin, Yung C.; King, Galen

    2010-09-01

    Mechanisms of energy transport during ultrashort laser pulses (USLPs) ablation are investigated in this paper. Nonequilibrium electron-transport, material ionization, as well as density change effects, are studied using atomistic models--the molecular dynamics (MD) and Monte Carlo (MC) methods, in addition to the previously studied laser absorption, heat conduction, and stress wave propagation. The target material is treated as consisting of two subsystems: valence-electron system and lattice system. MD method is applied to analyze the motion of atoms while MC method is applied for simulating electron dynamics and multiscattering events between particles. Early-time laser-energy absorption and redistribution as well as later-time material ablation and expansion processes are analyzed. This model is validated in terms of ablation depth, lattice/electron temperature distribution as well as evolution, and plume front velocity, through comparisons with experimental or theoretical results in literature. It is generally believed that the hydrodynamic motion of the ablated material is negligible for USLP but this study shows it is true only for its effect on laser-energy deposition. This study shows that the consideration of hydrodynamic expansion and fast density change in both electron and lattice systems is important for obtaining a reliable energy transport mechanism in the locally heated zone.

  8. Laser ablation of a turbid medium: Modeling and experimental results

    SciTech Connect

    Brygo, F.; Semerok, A.; Weulersse, J.-M.; Thro, P.-Y.; Oltra, R.

    2006-08-01

    Q-switched Nd:YAG laser ablation of a turbid medium (paint) is studied. The optical properties (absorption coefficient, scattering coefficient, and its anisotropy) of a paint are determined with a multiple scattering model (three-flux model), and from measurements of reflection-transmission of light through thin layers. The energy deposition profiles are calculated at wavelengths of 532 nm and 1.064 {mu}m. They are different from those described by a Lambert-Beer law. In particular, the energy deposition of the laser beam is not maximum on the surface but at some depth inside the medium. The ablated rate was measured for the two wavelengths and compared with the energy deposition profile predicted by the model. This allows us to understand the evolution of the ablated depth with the wavelength: the more the scattering coefficient is higher, the more the ablated depth and the threshold fluence of ablation decrease.

  9. Dynamics of the plumes produced by ultrafast laser ablation of metals

    SciTech Connect

    Donnelly, T.; Lunney, J. G.; Amoruso, S.; Bruzzese, R.; Wang, X.; Ni, X.

    2010-08-15

    We have analyzed ultrafast laser ablation of a metallic target (Nickel) in high vacuum addressing both expansion dynamics of the various plume components (ionic and nanoparticle) and basic properties of the ultrafast laser ablation process. While the ion temporal profile and ion angular distribution were analyzed by means of Langmuir ion probe technique, the angular distribution of the nanoparticulate component was characterized by measuring the thickness map of deposition on a transparent substrate. The amount of ablated material per pulse was found by applying scanning white light interferometry to craters produced on a stationary target. We have also compared the angular distribution of both the ionic and nanoparticle components with the Anisimov model. While the agreement for the ion angular distribution is very good at any laser fluence (from ablation threshold up to {approx_equal}1 J/cm{sup 2}), some discrepancies of nanoparticle plume angular distribution at fluencies above {approx_equal}0.4 J/cm{sup 2} are interpreted in terms of the influence of the pressure exerted by the nascent atomic plasma plume on the initial hydrodynamic evolution of the nanoparticle component. Finally, analyses of the fluence threshold and maximum ablation depth were also carried out, and compared to predictions of theoretical models. Our results indicate that the absorbed energy is spread over a length comparable with the electron diffusion depth L{sub c} ({approx_equal}30 nm) of Ni on the timescale of electron-phonon equilibration and that a logarithmic dependence is well-suited for the description of the variation in the ablation depth on laser fluence in the investigated range.

  10. Numerical investigation on target implosions driven by radiation ablation and shock compression in dynamic hohlraums

    SciTech Connect

    Xiao, Delong; Sun, Shunkai; Zhao, Yingkui; Ding, Ning; Wu, Jiming; Dai, Zihuan; Yin, Li; Zhang, Yang; Xue, Chuang

    2015-05-15

    In a dynamic hohlraum driven inertial confinement fusion (ICF) configuration, the target may experience two different kinds of implosions. One is driven by hohlraum radiation ablation, which is approximately symmetric at the equator and poles. The second is caused by the radiating shock produced in Z-pinch dynamic hohlraums, only taking place at the equator. To gain a symmetrical target implosion driven by radiation ablation and avoid asymmetric shock compression is a crucial issue in driving ICF using dynamic hohlraums. It is known that when the target is heated by hohlraum radiation, the ablated plasma will expand outward. The pressure in the shocked converter plasma qualitatively varies linearly with the material temperature. However, the ablation pressure in the ablated plasma varies with 3.5 power of the hohlraum radiation temperature. Therefore, as the hohlraum temperature increases, the ablation pressure will eventually exceed the shock pressure, and the expansion of the ablated plasma will obviously weaken the shock propagation and decrease its velocity after propagating into the ablator plasma. Consequently, longer time duration is provided for the symmetrical target implosion driven by radiation ablation. In this paper these processes are numerically investigated by changing drive currents or varying load parameters. The simulation results show that a critical hohlraum radiation temperature is needed to provide a high enough ablation pressure to decelerate the shock, thus providing long enough time duration for the symmetric fuel compression driven by radiation ablation.

  11. Low temperature ablation models made by pressure/vacuum application

    NASA Technical Reports Server (NTRS)

    Fischer, M. C.; Heier, W. C.

    1970-01-01

    Method developed employs high pressure combined with strong vacuum force to compact ablation models into desired conical shape. Technique eliminates vapor hazard and results in high material density providing excellent structural integrity.

  12. Preparing the anatomical model for ablation of unresectable liver tumor

    PubMed Central

    2014-01-01

    Introduction Nowadays the best treatment of the primary and secondary hepatic tumor is surgical resection, but only 5–15% of all patient with hepatocellular carcinoma and 20–25% of all patients with liver metastases are indicated for resection. In these cases some kind of ablation and other technique could be used. Aim To present the methodology of preparing the anatomical model for ablation of unresectable liver tumor. Material and methods The presented method is based on abdomen computed tomography (CT) dynamic examination. Three methods of segmentation are used: rolling vector for liver volume, modified Frangi filter for liver vessels, and fuzzy expert system with initial region-of-interest anisotropic filtration for liver metastases. Segmentation results are the input data for creating 3D anatomical models in the form of B-spline curves and surfaces performing the surface global interpolation algorithm. A graphical user interface for presentation and evaluation of models, presented in color against DICOM images in grayscale, is designed and implemented. Results The proposed approach was tested on 20 abdominal CT obtained from the Department of Clinical Radiology of Silesian Medical University. The lack of a “gold standard” provides for the correction of the results. Conclusions Preparation of the anatomical model is one of the important early stages of the use of image-based navigation systems. This process could not take place in a fully automatic manner and verification of the results obtained is performed by the radiologist. Using the above anatomical model in surgical workflow is presented. PMID:25097694

  13. Ultrashort laser ablation of bulk copper targets: Dynamics and size distribution of the generated nanoparticles

    SciTech Connect

    Tsakiris, N.; Gill-Comeau, M.; Lewis, L. J.; Anoop, K. K.; Ausanio, G.; Bruzzese, R.; Amoruso, S.

    2014-06-28

    We address the role of laser pulse fluence on expansion dynamics and size distribution of the nanoparticles produced by irradiating a metallic target with an ultrashort laser pulse in a vacuum, an issue for which contrasting indications are present in the literature. To this end, we have carried out a combined theoretical and experimental analysis of laser ablation of a bulk copper target with ≈50 fs, 800 nm pulses, in an interval of laser fluencies going from few to several times the ablation threshold. On one side, molecular dynamics simulations, with two-temperature model, describe the decomposition of the material through the analysis of the evolution of thermodynamic trajectories in the material phase diagram, and allow estimating the size distribution of the generated nano-aggregates. On the other side, atomic force microscopy of less than one layer nanoparticles deposits on witness plates, and fast imaging of the nanoparticles broadband optical emission provide the corresponding experimental characterization. Both experimental and numerical findings agree on a size distribution characterized by a significant fraction (≈90%) of small nanoparticles, and a residual part (≈10%) spanning over a rather large size interval, evidencing a weak dependence of the nanoparticles sizes on the laser pulse fluence. Numerical and experimental findings show a good degree of consistency, thus suggesting that modeling can realistically support the search for experimental methods leading to an improved control over the generation of nanoparticles by ultrashort laser ablation.

  14. Spatiotemporal electrophysiological changes in a murine ablation model

    PubMed Central

    Bernstein, Scott A.; Duggirala, Srikant; Floberg, Michael; Elfvendal, Pehr; Kuznekoff, Laura M.; Lader, Joshua M.; Vasquez, Carolina; Morley, Gregory E.

    2011-01-01

    Aims High recurrence rates after complex radiofrequency ablation procedures, such as for atrial fibrillation, remain a major clinical problem. Local electrophysiological changes that occur following cardiac ablation therapy are incompletely described in the literature. The purpose of this study was to determine whether alterations in conduction velocity, action potential duration (APD), and effective refractory period resolve dynamically following cardiac ablation. Methods and results  Lesions were delivered to the right ventricle of mice using a subxiphoid approach. The sham-operated control group (SHAM) received the same procedure without energy delivery. Hearts were isolated at 0, 1, 7, 30, and 60 days following the procedure and electrophysiological parameters were obtained using high-resolution optical mapping with a voltage-sensitive dye. Conduction velocity was significantly decreased at the lesion border in the 0, 7, and 30 day groups compared to SHAM. APD70 at the lesion border was significantly increased at all time points compared to SHAM. Effective refractory period was significantly increased at the lesion border at 0, 1, 7, and 30 days but not at 60 days post-ablation. This study demonstrated that post-ablation electrophysiological changes take place immediately following energy delivery and resolve within 60 days. Conclusions Cardiac ablation causes significant electrophysiological changes both within the lesion and beyond the border zone. Late recovery of electrical conduction in individual lesions is consistent with clinical data demonstrating that arrhythmia recurrence is associated with failure to maintain bi-directional conduction block. PMID:21712278

  15. Development and numerical solution of a mechanistic model for corneal tissue ablation with the 193 nm argon fluoride excimer laser

    NASA Astrophysics Data System (ADS)

    Fisher, Brian T.; Hahn, David W.

    2007-02-01

    We detail the development and implementation of a global ablation model that incorporates a dynamically changing tissue absorption coefficient. Detailed spectroscopic measurements rule out plasma-shielding effects during the laser-tissue interaction and thereby support a photochemical mechanism. The model predicts ablation rate behavior that agrees well with a variety of experimental ablation rate data and that substantially deviates from a static Beer-Lambert model. The dynamic model predicts an enhancement in the tissue absorption coefficient of about 25%-50% as compared with the initial, static value. In addition, the model predicts an increase in the tissue ablation rate as corneal hydration increases, which may provide additional insight into variations in refractive surgery outcome.

  16. Modeling sublimation of a charring ablator

    NASA Technical Reports Server (NTRS)

    Balhoff, J. F.; Pike, R. W.

    1973-01-01

    The Hertz-Knudsen analysis is shown to accurately predict the sublimation rate from a charring ablator. Porosity is shown to have a significant effect on the surface temperature. The predominant carbon species found in the vapor is C3, which agrees well with the results of previous investigations.

  17. Studies of the Dynamics of Ablation Stream development in Wire Arrays on COBRA

    NASA Astrophysics Data System (ADS)

    Greenly, John; Martin, Matthew; Seyler, Charles

    2007-11-01

    Wire-array simulations with the 3D GORGON code (see adjoining poster by Martin et al.) show a characteristic evolution in the development of streams of ablated material ejected from the wires toward the array axis. In simulations of aluminum arrays, the fundamental behavior occurs in two steps. The first is the development of coronal plasma that is trapped around the wire core in closed ``local'' magnetic flux. This coronal plasma, together with the closed flux, is then accelerated inward after a certain ``dwell'' time, leaving behind a radially distributed current density with entirely open ``global'' magnetic field lines, producing smooth, distributed acceleration of ablated plasma inward from the wire core until the onset of the final implosion. Interpretation of these dynamics in terms of simple physical modeling will be discussed, and experimental evidence of these phenomena from imaging and magnetic field diagnostics on arrays on the COBRA facility at Cornell will be presented.

  18. Ablation and Thermal Response Property Model Validation for Phenolic Impregnated Carbon Ablator

    NASA Technical Reports Server (NTRS)

    Milos, F. S.; Chen, Y.-K.

    2009-01-01

    Phenolic Impregnated Carbon Ablator was the heatshield material for the Stardust probe and is also a candidate heatshield material for the Orion Crew Module. As part of the heatshield qualification for Orion, physical and thermal properties were measured for newly manufactured material, included emissivity, heat capacity, thermal conductivity, elemental composition, and thermal decomposition rates. Based on these properties, an ablation and thermal-response model was developed for temperatures up to 3500 K and pressures up to 100 kPa. The model includes orthotropic and pressure-dependent thermal conductivity. In this work, model validation is accomplished by comparison of predictions with data from many arcjet tests conducted over a range of stagnation heat flux and pressure from 107 Watts per square centimeter at 2.3 kPa to 1100 Watts per square centimeter at 84 kPa. Over the entire range of test conditions, model predictions compare well with measured recession, maximum surface temperatures, and in depth temperatures.

  19. Modeling and validation of microwave ablations with internal vaporization.

    PubMed

    Chiang, Jason; Birla, Sohan; Bedoya, Mariajose; Jones, David; Subbiah, Jeyam; Brace, Christopher L

    2015-02-01

    Numerical simulation is increasingly being utilized for computer-aided design of treatment devices, analysis of ablation growth, and clinical treatment planning. Simulation models to date have incorporated electromagnetic wave propagation and heat conduction, but not other relevant physics such as water vaporization and mass transfer. Such physical changes are particularly noteworthy during the intense heat generation associated with microwave heating. In this paper, a numerical model was created that integrates microwave heating with water vapor generation and transport by using porous media assumptions in the tissue domain. The heating physics of the water vapor model was validated through temperature measurements taken at locations 5, 10, and 20 mm away from the heating zone of the microwave antenna in homogenized ex vivo bovine liver setup. Cross-sectional area of water vapor transport was validated through intraprocedural computed tomography (CT) during microwave ablations in homogenized ex vivo bovine liver. Iso-density contours from CT images were compared to vapor concentration contours from the numerical model at intermittent time points using the Jaccard index. In general, there was an improving correlation in ablation size dimensions as the ablation procedure proceeded, with a Jaccard index of 0.27, 0.49, 0.61, 0.67, and 0.69 at 1, 2, 3, 4, and 5 min, respectively. This study demonstrates the feasibility and validity of incorporating water vapor concentration into thermal ablation simulations and validating such models experimentally. PMID:25330481

  20. Modeling and validation of microwave ablations with internal vaporization.

    PubMed

    Chiang, Jason; Birla, Sohan; Bedoya, Mariajose; Jones, David; Subbiah, Jeyam; Brace, Christopher L

    2015-02-01

    Numerical simulation is increasingly being utilized for computer-aided design of treatment devices, analysis of ablation growth, and clinical treatment planning. Simulation models to date have incorporated electromagnetic wave propagation and heat conduction, but not other relevant physics such as water vaporization and mass transfer. Such physical changes are particularly noteworthy during the intense heat generation associated with microwave heating. In this paper, a numerical model was created that integrates microwave heating with water vapor generation and transport by using porous media assumptions in the tissue domain. The heating physics of the water vapor model was validated through temperature measurements taken at locations 5, 10, and 20 mm away from the heating zone of the microwave antenna in homogenized ex vivo bovine liver setup. Cross-sectional area of water vapor transport was validated through intraprocedural computed tomography (CT) during microwave ablations in homogenized ex vivo bovine liver. Iso-density contours from CT images were compared to vapor concentration contours from the numerical model at intermittent time points using the Jaccard index. In general, there was an improving correlation in ablation size dimensions as the ablation procedure proceeded, with a Jaccard index of 0.27, 0.49, 0.61, 0.67, and 0.69 at 1, 2, 3, 4, and 5 min, respectively. This study demonstrates the feasibility and validity of incorporating water vapor concentration into thermal ablation simulations and validating such models experimentally.

  1. Modeling and Validation of Microwave Ablations with Internal Vaporization

    PubMed Central

    Chiang, Jason; Birla, Sohan; Bedoya, Mariajose; Jones, David; Subbiah, Jeyam; Brace, Christopher L.

    2014-01-01

    Numerical simulation is increasingly being utilized for computer-aided design of treatment devices, analysis of ablation growth, and clinical treatment planning. Simulation models to date have incorporated electromagnetic wave propagation and heat conduction, but not other relevant physics such as water vaporization and mass transfer. Such physical changes are particularly noteworthy during the intense heat generation associated with microwave heating. In this work, a numerical model was created that integrates microwave heating with water vapor generation and transport by using porous media assumptions in the tissue domain. The heating physics of the water vapor model was validated through temperature measurements taken at locations 5, 10 and 20 mm away from the heating zone of the microwave antenna in homogenized ex vivo bovine liver setup. Cross-sectional area of water vapor transport was validated through intra-procedural computed tomography (CT) during microwave ablations in homogenized ex vivo bovine liver. Iso-density contours from CT images were compared to vapor concentration contours from the numerical model at intermittent time points using the Jaccard Index. In general, there was an improving correlation in ablation size dimensions as the ablation procedure proceeded, with a Jaccard Index of 0.27, 0.49, 0.61, 0.67 and 0.69 at 1, 2, 3, 4, and 5 minutes. This study demonstrates the feasibility and validity of incorporating water vapor concentration into thermal ablation simulations and validating such models experimentally. PMID:25330481

  2. Monte Carlo Simulation of Laser-Ablated Particle Splitting Dynamic in a Low Pressure Inert Gas

    NASA Astrophysics Data System (ADS)

    Ding, Xuecheng; Zhang, Zicai; Liang, Weihua; Chu, Lizhi; Deng, Zechao; Wang, Yinglong

    2016-06-01

    A Monte Carlo simulation method with an instantaneous density dependent mean-free-path of the ablated particles and the Ar gas is developed for investigating the transport dynamics of the laser-ablated particles in a low pressure inert gas. The ablated-particle density and velocity distributions are analyzed. The force distributions acting on the ablated particles are investigated. The influence of the substrate on the ablated-particle velocity distribution and the force distribution acting on the ablated particles are discussed. The Monte Carlo simulation results approximately agree with the experimental data at the pressure of 8 Pa to 17 Pa. This is helpful to investigate the gas phase nucleation and growth mechanism of nanoparticles. supported by the Natural Science Foundation of Hebei Province, China (No. A2015201166) and the Natural Science Foundation of Hebei University, China (No. 2013-252)

  3. Gas Effect On Plasma Dynamics Of Laser Ablation Zinc Oxide

    SciTech Connect

    Abdelli-Messaci, S.; Kerdja, T.; Lafane, S.; Malek, S.

    2008-09-23

    In order to synthesis zinc oxide thin films and nanostructures, laser ablation of ZnO target into both vacuum and oxygen atmosphere was performed. The gas effect on the plume dynamics was studied for O{sub 2} pressures varied between 10{sup -2} to 70 mbar. Plasma plume evolution was investigated by ICCD camera fast imaging. The plasma was created by a KrF excimer laser ({lambda} = 248 nm, {tau} = 25 ns) at a fluence of 2 J/cm{sup 2}. The light emitted by the plume was observed along the perpendicular to the ejection direction through a fast intensified charge-coupled device (ICCD). We have found that the plasma dynamics is very affected by the gas pressures. The photographs reveal the stratification of plasma into slow and fast components for 0.5 mbar O{sub 2} pressures and beyond. The photographs also show the apparition of hydrodynamic instabilities which are related to chemical reactions between the plasma and the surrounding gas for a certain range of pressures.

  4. Adjustment of ablation shapes and subwavelength ripples based on electron dynamics control by designing femtosecond laser pulse trains

    SciTech Connect

    Yuan Yanping; Jiang Lan; Li Xin; Wang Cong

    2012-11-15

    A quantum model is proposed to investigate femtosecond laser pulse trains processing of dielectrics by including the plasma model with the consideration of laser particle-wave duality. Central wavelengths (400 nm and 800 nm) strongly impact the surface plasmon field distribution, the coupling field intensity distribution (between the absorbed intensity and the surface plasma), and the distribution of transient localized free electron density in the material. This, in turn, significantly changes the localized transient optical/thermal properties during laser materials processing. The effects of central wavelengths on ablation shapes and subwavelength ripples are discussed. The simulation results show that: (1) ablation shapes and the spacing of subwavelength ripples can be adjusted by localized transient electron dynamics control using femtosecond laser pulse trains; (2) the adjustment of the radii of ablation shapes is stronger than that of the periods of subwavelength ripples.

  5. Dynamic stabilization of Rayleigh-Taylor instability: Experiments with Newtonian fluids as surrogates for ablation fronts

    SciTech Connect

    Rodriguez Prieto, G.; Piriz, A. R.; Lopez Cela, J. J.; Tahir, N. A.

    2013-01-15

    A previous theory on dynamic stabilization of Rayleigh-Taylor instability at interfaces between Newtonian fluids is reformulated in order to make evident the analogy of this problem with the related one on dynamic stabilization of ablation fronts in the framework of inertial confinement fusion. Explicit analytical expressions are obtained for the boundaries of the dynamically stable region which turns out to be completely analogue to the stability charts obtained for the case of ablation fronts. These results allow proposing experiments with Newtonian fluids as surrogates for studying the case of ablation fronts. Experiments with Newtonian fluids are presented which demonstrate the validity of the theoretical approach and encourage to pursue experimental research on ablation fronts to settle the feasibility of dynamic stabilization in the inertial confinement fusion scenario.

  6. Saphenous Venous Ablation with Hot Contrast in a Canine Model

    SciTech Connect

    Prasad, Amit Qian Zhong; Kirsch, David; Eissa, Marna; Narra, Pavan; Lopera, Jorge; Espinoza, Carmen G.; Castaneda, Wifrido

    2008-01-15

    Purpose. To determine the feasibility, efficacy, and safety of thermal ablation of the saphenous vein with hot contrast medium. Methods. Twelve saphenous veins of 6 dogs were percutaneously ablated with hot contrast medium. In all animals, ablation was performed in the vein of one leg, followed by ablation in the contralateral side 1 month later. An occlusion balloon catheter was placed in the infragenicular segment of the saphenous vein via a jugular access to prevent unwanted thermal effects on the non-target segment of the saphenous vein. After inflation of the balloon, 10 ml of hot contrast medium was injected under fluoroscopic control through a sheath placed in the saphenous vein above the ankle. A second 10 ml injection of hot contrast medium was made after 5 min in each vessel. Venographic follow-up of the ablated veins was performed at 1 month (n = 12) and 2 months (n = 6). Results. Follow-up venograms showed that all ablated venous segments were occluded at 1 month. In 6 veins which were followed up to 2 months, 4 (66%) remained occluded, 1 (16%) was partially patent, and the remaining vein (16%) was completely patent. In these latter 2 cases, an inadequate amount of hot contrast was delivered to the lumen due to a closed balloon catheter downstream which did not allow contrast to displace blood within the vessel. Discussion. Hot contrast medium thermal ablation of the saphenous vein appears feasible, safe, and effective in the canine model, provided an adequate amount of embolization agent is used.

  7. Endometrial ablation

    MedlinePlus

    Hysteroscopy-endometrial ablation; Laser thermal ablation; Endometrial ablation-radiofrequency; Endometrial ablation-thermal balloon ablation; Rollerball ablation; Hydrothermal ablation; Novasure ablation

  8. Multidimensional modeling of pyrolysis gas transport inside orthotropic charring ablators

    NASA Astrophysics Data System (ADS)

    Weng, Haoyue

    During hypersonic atmospheric entry, spacecraft are exposed to enormous aerodynamic heat. To prevent the payload from overheating, charring ablative materials are favored to be applied as the heat shield at the exposing surface of the vehicle. Accurate modeling not only prevents mission failures, but also helps reduce cost. Existing models were mostly limited to one-dimensional and discrepancies were shown against measured experiments and flight-data. To help improve the models and analyze the charring ablation problems, a multidimensional material response module is developed, based on a finite volume method framework. The developed computer program is verified through a series of test-cases, and through code-to-code comparisons with a validated code. Several novel models are proposed, including a three-dimensional pyrolysis gas transport model and an orthotropic material model. The effects of these models are numerically studied and demonstrated to be significant.

  9. Dynamics of laser ablation of microparticles prior to nanoparticle generation

    SciTech Connect

    Lee, Jaemyoung; Becker, Michael F.; Keto, John W.

    2001-06-15

    To better understand the process of nanoparticle formation when microspheres are ablated by a high-energy laser pulse, we investigated the Nd:YAG laser-induced breakdown of 20 {mu}m glass microspheres using time-resolved optical shadow images and Schlieren images. Time-resolved imaging showed the location of the initial breakdown and the shockwave motion over its first 300 {mu}m of expansion. From these measurements, we determined the shockwave velocity dependence on laser fluence. Measured shockwave velocities were in the range of 1{endash}10 km/s. We also developed a numerical model that simulated breakdown in the glass microsphere and the propagation of this disturbance through the edge of the sphere where it could launch an air shock. Our objective was to simulate the shockwave velocity dependence on laser fluence and to generate glass density, temperature, and mass velocity profiles after breakdown. The simulation and experimental data compared favorably. {copyright} 2001 American Institute of Physics.

  10. Particle-based ablation model for faint meteors

    NASA Astrophysics Data System (ADS)

    Stokan, E.; Campbell-Brown, M.

    2014-07-01

    Modeling the ablation of meteoroids as they enter the atmosphere is a way of determining their physical structure and elemental composition. This can provide insight into the structure of parent bodies when combined with an orbit computed from observations. The Canadian Automated Meteor Observatory (CAMO) is a source of new, high-resolution observations of faint meteors [1]. These faint objects tend to have pre-atmospheric masses around 10^{-5} kg, corresponding to a radius of 1 mm. A wide-field camera with a 28° field of view provides guidance to a high-resolution camera that tracks meteors in flight with 1.5° field of view. Meteors are recorded with a scale of 4 m per pixel at a range of 135 km, at 110 frames per second, allowing us to investigate detailed meteor morphology. This serves as an important new constraint for ablation models, in addition to meteor brightness (lightcurves) and meteoroid deceleration. High-resolution observations of faint meteors have revealed that contemporary ablation models are not able to predict meteor morphology, even while matching the observed lightcurve and meteoroid deceleration [2]. This implies that other physical processes, in addition to fragmentation, must be considered for faint meteor ablation. We present a new, particle-based approach to modeling the ablation of small meteoroids. In this model, we simulate the collisions between atmospheric particles and the meteoroid to determine the rate of evaporation and deceleration. Subsequent collisions simulated between evaporated meteoroid particles and ambient atmospheric particles then produce light that would be observed by high-resolution cameras. Preliminary results show simultaneous agreement with meteor morphology, lightcurves, and decelerations recorded with CAMO. A sample comparison of simulated and observed meteor morphology is given in the attached figure. Several meteoroids are well-represented as solid, stony bodies, but some require modeling as a dustball [3

  11. Experimental and computational study of complex shockwave dynamics in laser ablation plumes in argon atmosphere

    SciTech Connect

    Harilal, S. S.; Miloshevsky, G. V.; Diwakar, P. K.; LaHaye, N. L.; Hassanein, A.

    2012-08-15

    We investigated spatio-temporal evolution of ns laser ablation plumes at atmospheric pressure, a favored condition for laser-induced breakdown spectroscopy and laser-ablation inductively coupled plasma mass-spectrometry. The 1064 nm, 6 ns pulses from a Nd:YAG laser were focused on to an Al target and the generated plasma was allowed to expand in 1 atm Ar. The hydrodynamic expansion features were studied using focused shadowgraphy and gated 2 ns self-emission visible imaging. Shadowgram images showed material ejection and generation of shock fronts. A secondary shock is observed behind the primary shock during the time window of 100-500 ns with instabilities near the laser cone angle. By comparing the self-emission images obtained using fast photography, it is concluded that the secondary shocks observed in the shadowgraphy were generated by fast moving target material. The plume front estimates using fast photography exhibited reasonable agreement with data obtained from shadowgraphy at early times {<=}400 ns. However, at later times, fast photography images showed plume confinement while the shadowgraphic images showed propagation of the plume front even at greater times. The structure and dynamics of the plume obtained from optical diagnostic tools were compared to numerical simulations. We have shown that the main features of plume expansion in ambient Ar observed in the experiments can be reproduced using a continuum hydrodynamics model which provided valuable insight into the expansion dynamics and shock structure of the plasma plume.

  12. Experimental and computational study of complex shockwave dynamics in laser ablation plumes in argon atmosphere

    NASA Astrophysics Data System (ADS)

    Harilal, S. S.; Miloshevsky, G. V.; Diwakar, P. K.; LaHaye, N. L.; Hassanein, A.

    2012-08-01

    We investigated spatio-temporal evolution of ns laser ablation plumes at atmospheric pressure, a favored condition for laser-induced breakdown spectroscopy and laser-ablation inductively coupled plasma mass-spectrometry. The 1064 nm, 6 ns pulses from a Nd:YAG laser were focused on to an Al target and the generated plasma was allowed to expand in 1 atm Ar. The hydrodynamic expansion features were studied using focused shadowgraphy and gated 2 ns self-emission visible imaging. Shadowgram images showed material ejection and generation of shock fronts. A secondary shock is observed behind the primary shock during the time window of 100-500 ns with instabilities near the laser cone angle. By comparing the self-emission images obtained using fast photography, it is concluded that the secondary shocks observed in the shadowgraphy were generated by fast moving target material. The plume front estimates using fast photography exhibited reasonable agreement with data obtained from shadowgraphy at early times ≤400 ns. However, at later times, fast photography images showed plume confinement while the shadowgraphic images showed propagation of the plume front even at greater times. The structure and dynamics of the plume obtained from optical diagnostic tools were compared to numerical simulations. We have shown that the main features of plume expansion in ambient Ar observed in the experiments can be reproduced using a continuum hydrodynamics model which provided valuable insight into the expansion dynamics and shock structure of the plasma plume.

  13. Plume dynamics of cross-beam pulsed-laser ablation of graphite

    SciTech Connect

    Sanchez Ake, C.; Sangines de Castro, R.; Sobral, H.; Villagran-Muniz, M.

    2006-09-01

    The dynamics of the interaction between two plasmas induced by cross-beam pulsed-laser ablation was analyzed by time resolved optical emission spectroscopy and fast photography. The plasmas were created in vacuum by irradiating two perpendicular graphite targets with an excimer (248 nm) and a Nd:yttrium-aluminum-garnet (1064 nm) laser. In this configuration, a laser is focused onto a target generating a highly directed plume; subsequently, an additional laser produces a second plasma from the perpendicular target which expands through the first plume. Collisional processes cause a reduction of the kinetic energy of the second plume species as compared to the single pulse experiment. For a fixed delay between lasers of 2 {mu}s, the second plume was divided in two perpendicular directions. The dynamics of this plasma has been compared with laser-induced plume propagation through a background gas in terms of the drag model.

  14. Microwave ablation energy delivery: Influence of power pulsing on ablation results in an ex vivo and in vivo liver model

    PubMed Central

    Bedoya, Mariajose; del Rio, Alejandro Muñoz; Chiang, Jason; Brace, Christopher L.

    2014-01-01

    Purpose: The purpose of this study was to compare the impact of continuous and pulsed energy deliveries on microwave ablation growth and shape in unperfused and perfused liver models. Methods: A total of 15 kJ at 2.45 GHz was applied to ex vivo bovine liver using one of five delivery methods (n = 50 total, 10 per group): 25 W continuous for 10 min (25 W average), 50 W continuous for 5 min (50 W average), 100 W continuous for 2.5 min (100 W average), 100 W pulsed for 10 min (25 W average), and 100 W pulsed for 5 min (50 W average). A total of 30 kJ was applied to in vivo porcine livers (n = 35, 7 per group) using delivery methods similar to the ex vivo study, but with twice the total ablation time to offset heat loss to blood perfusion. Temperatures were monitored 5–20 mm from the ablation antenna, with values over 60 °C indicating acute cellular necrosis. Comparisons of ablation size and shape were made between experimental groups based on total energy delivery, average power applied, and peak power using ANOVA with post-hoc pairwise tests. Results: No significant differences were noted in ablation sizes or circularities between pulsed and continuous groups in ex vivo tissue. Temperature data demonstrated more rapid heating in pulsed ablations, suggesting that pulsing may overcome blood perfusion and coagulate tissues more rapidly in vivo. Differences in ablation size and shape were noted in vivo despite equivalent energy delivery among all groups. Overall, the largest ablation volume in vivo was produced with 100 W continuous for 5 min (265.7 ± 208.1 cm3). At 25 W average, pulsed-power ablation volumes were larger than continuous-power ablations (67.4 ± 34.5 cm3 versus 23.6 ± 26.5 cm3, P = 0.43). Similarly, pulsed ablations produced significantly greater length (P ≤ 0.01), with increase in diameter (P = 0.09) and a slight decrease in circularity (P = 0.97). When comparing 50 W average power groups, moderate differences in size were noted (P ≥ 0.06) and

  15. Thermal-mechanical modeling of laser ablation hybrid machining

    NASA Astrophysics Data System (ADS)

    Matin, Mohammad Kaiser

    2001-08-01

    Hard, brittle and wear-resistant materials like ceramics pose a problem when being machined using conventional machining processes. Machining ceramics even with a diamond cutting tool is very difficult and costly. Near net-shape processes, like laser evaporation, produce micro-cracks that require extra finishing. Thus it is anticipated that ceramic machining will have to continue to be explored with new-sprung techniques before ceramic materials become commonplace. This numerical investigation results from the numerical simulations of the thermal and mechanical modeling of simultaneous material removal from hard-to-machine materials using both laser ablation and conventional tool cutting utilizing the finite element method. The model is formulated using a two dimensional, planar, computational domain. The process simulation acronymed, LAHM (Laser Ablation Hybrid Machining), uses laser energy for two purposes. The first purpose is to remove the material by ablation. The second purpose is to heat the unremoved material that lies below the ablated material in order to ``soften'' it. The softened material is then simultaneously removed by conventional machining processes. The complete solution determines the temperature distribution and stress contours within the material and tracks the moving boundary that occurs due to material ablation. The temperature distribution is used to determine the distance below the phase change surface where sufficient ``softening'' has occurred, so that a cutting tool may be used to remove additional material. The model incorporated for tracking the ablative surface does not assume an isothermal melt phase (e.g. Stefan problem) for laser ablation. Both surface absorption and volume absorption of laser energy as function of depth have been considered in the models. LAHM, from the thermal and mechanical point of view is a complex machining process involving large deformations at high strain rates, thermal effects of the laser, removal of

  16. Femtosecond-laser ablation dynamics of dielectrics: basics and applications for thin films.

    PubMed

    Balling, P; Schou, J

    2013-03-01

    Laser ablation of dielectrics by ultrashort laser pulses is reviewed. The basic interaction between ultrashort light pulses and the dielectric material is described, and different approaches to the modeling of the femtosecond ablation dynamics are reviewed. Material excitation by ultrashort laser pulses is induced by a combination of strong-field excitation (multi-photon and tunnel excitation), collisional excitation (potentially leading to an avalanche process), and absorption in the plasma consisting of the electrons excited to the conduction band. It is discussed how these excitation processes can be described by various rate-equation models in combination with different descriptions of the excited electrons. The optical properties of the highly excited dielectric undergo a rapid change during the laser pulse, which must be included in a detailed modeling of the excitations. The material ejected from the dielectric following the femtosecond-laser excitation can potentially be used for thin-film deposition. The deposition rate is typically much smaller than that for nanosecond lasers, but film production by femtosecond lasers does possess several attractive features. First, the strong-field excitation makes it possible to produce films of materials that are transparent to the laser light. Second, the highly localized excitation reduces the emission of larger material particulates. Third, lasers with ultrashort pulses are shown to be particularly useful tools for the production of nanocluster films. The important question of the film stoichiometry relative to that of the target will be thoroughly discussed in relation to the films reported in the literature. PMID:23439493

  17. Flight dynamics simulation of lightcraft propelled by laser ablation

    NASA Astrophysics Data System (ADS)

    Ballard, C. G.; Anderson, K. S.; Myrabo, L. N.

    2006-05-01

    A six degree-of-freedom (DOF) dynamic model was developed to provide insight into the flight behavior of Type 200 Lightcraft, and to serve as a research tool for developing future engine-vehicle configurations for laser launching of nano-satellites (1-10 kg). Accurate engine, beam, and aerodynamics models are included to improve the predictive capability of the 6-DOF code. The aerodynamic forces of lift, drag, and aerodynamic pitching moment were derived from Fluent ® computational fluid dynamics predictions, and calibrated against limited existing wind tunnel data. To facilitate 6-DOF model validation, simulation results are compared with video analysis of flights under comparable conditions. Despite current limitations of the 6-DOF model, the results compared well with experimental flight trajectory data.

  18. Mathematical modeling of radiofrequency ablation for varicose veins.

    PubMed

    Choi, Sun Young; Kwak, Byung Kook; Seo, Taewon

    2014-01-01

    We present a three-dimensional mathematical model for the study of radiofrequency ablation (RFA) with blood flow for varicose vein. The model designed to analyze temperature distribution heated by radiofrequency energy and cooled by blood flow includes a cylindrically symmetric blood vessel with a homogeneous vein wall. The simulated blood velocity conditions are U = 0, 1, 2.5, 5, 10, 20, and 40 mm/s. The lower the blood velocity, the higher the temperature in the vein wall and the greater the tissue damage. The region that is influenced by temperature in the case of the stagnant flow occupies approximately 28.5% of the whole geometry, while the region that is influenced by temperature in the case of continuously moving electrode against the flow direction is about 50%. The generated RF energy induces a temperature rise of the blood in the lumen and leads to an occlusion of the blood vessel. The result of the study demonstrated that higher blood velocity led to smaller thermal region and lower ablation efficiency. Since the peak temperature along the venous wall depends on the blood velocity and pullback velocity, the temperature distribution in the model influences ablation efficiency. The vein wall absorbs more energy in the low pullback velocity than in the high one. PMID:25587351

  19. Mathematical Modeling of Radiofrequency Ablation for Varicose Veins

    PubMed Central

    Choi, Sun Young; Kwak, Byung Kook

    2014-01-01

    We present a three-dimensional mathematical model for the study of radiofrequency ablation (RFA) with blood flow for varicose vein. The model designed to analyze temperature distribution heated by radiofrequency energy and cooled by blood flow includes a cylindrically symmetric blood vessel with a homogeneous vein wall. The simulated blood velocity conditions are U = 0, 1, 2.5, 5, 10, 20, and 40 mm/s. The lower the blood velocity, the higher the temperature in the vein wall and the greater the tissue damage. The region that is influenced by temperature in the case of the stagnant flow occupies approximately 28.5% of the whole geometry, while the region that is influenced by temperature in the case of continuously moving electrode against the flow direction is about 50%. The generated RF energy induces a temperature rise of the blood in the lumen and leads to an occlusion of the blood vessel. The result of the study demonstrated that higher blood velocity led to smaller thermal region and lower ablation efficiency. Since the peak temperature along the venous wall depends on the blood velocity and pullback velocity, the temperature distribution in the model influences ablation efficiency. The vein wall absorbs more energy in the low pullback velocity than in the high one. PMID:25587351

  20. Femtosecond laser ablation of CuxZr1-x bulk metallic glasses: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Marinier, Sébastien; Lewis, Laurent J.

    2015-11-01

    Molecular-dynamics simulations combined with a two-temperature model are used to study laser ablation in CuxZr1-x (x =0.33 ,0.50 ,0.67 ) metallic glasses as well as crystalline CuZr2 in the C11b (MoSi2) structure. Ablation thresholds are found to be 430 ±10 ,450 ±10 ,510 ±10 , and 470 ±10 J/m 2 for a-Cu2Zr , a-CuZr, a-CuZr2, and c-CuZr2, respectively. The larger threshold in amorphous CuZr2 results from a weaker electron-phonon coupling and thus longer electron-ion equilibration time. We observe that the velocity of the pressure waves in the amorphous samples is not affected by the fluence, in contrast to the crystal; this is due to differences in the behavior of the shear modulus with increasing pressure. The heat-affected zone in the different systems is characterized in terms of the melting depth as well as inelastic deformations. The melting depth is found to be smaller in the crystal than in the amorphous targets because of its higher melting temperature. The inelastic deformations are investigated in terms of the von Mises shear strain invariant ηMises; the homogeneous nucleation of shear transformation zones is observed in the glass as reported in previous theoretical and experimental studies. The coalescence of the shear transformation zones is also found at higher fluence.

  1. Modeling of Heat Transfer and Ablation of Refractory Material Due to Rocket Plume Impingement

    NASA Technical Reports Server (NTRS)

    Harris, Michael F.; Vu, Bruce T.

    2012-01-01

    CR Tech's Thermal Desktop-SINDA/FLUINT software was used in the thermal analysis of a flame deflector design for Launch Complex 39B at Kennedy Space Center, Florida. The analysis of the flame deflector takes into account heat transfer due to plume impingement from expected vehicles to be launched at KSC. The heat flux from the plume was computed using computational fluid dynamics provided by Ames Research Center in Moffet Field, California. The results from the CFD solutions were mapped onto a 3-D Thermal Desktop model of the flame deflector using the boundary condition mapping capabilities in Thermal Desktop. The ablation subroutine in SINDA/FLUINT was then used to model the ablation of the refractory material.

  2. Dynamic Stabilization of the Ablative Rayleigh-Taylor Instability for Heavy Ion Fusion

    SciTech Connect

    Qin, Hong; Davidson, Ronald C.; Logan, B. Grant

    2012-10-04

    Dynamic stabilization of the ablative Rayleigh-Taylor instability of a heavy ion fusion target induced by a beam wobbling system is studied. Using a sharp-boundary model and Courant-Synder theory, it is shown, with an appropriately chosen modulation waveform, that the instability can be sta- bilized in certain parameter regimes. It is found that the stabilization e ect has a strong dependence on the modulation frequency and the waveform. Modulation with frequency comparable to the instability growth rate is the most e ective in terms of stabilizing the instability. A modulation with two frequency components can result in a reduction of the growth rate larger than the sum of that due to the two components when applied separately.

  3. Finite-element model for endometrial ablation systems

    NASA Astrophysics Data System (ADS)

    Ryan, Thomas P.; Platt, Robert C.; Humphries, Stanley, Jr.

    1998-04-01

    Ablation of the endometrium has become a viable treatment for dysfunctional bleeding of the uterus in women. Surgical applications of thermal ablation utilized a rolling electrode to ablate the inner uterine lining, but required practiced surgical skills and made it difficult to assess subsurface damage. Recently, various energy systems have been applied to the endometrium such as lasers, microwaves, RF electrodes, hot water balloons, and cryotherapy. A finite element model is presented to compare a multi-electrode, multiplexed RF device with a balloon containing hot fluid. The temperature fields in the uterine wall are plotted over time for various blood flow values. Assumptions of constant electrical conductivity are compared to temperature- dependent electrical conductivity. Temperatures are shown to be a maximum of about 10 - 20 degree(s)C higher when varying electrical conductivity is used. Results are also shown for cases with a 2 mm blood vessel in the field and how each device adjusts its operation to compensate for this heat sink. Damage integral results will be shown according to the time and temperature of the treatments.

  4. Ablation dynamics of Co/ZnS targets under double pulse femtosecond laser irradiation.

    PubMed

    Lopez-Quintas, Ignacio; Loriot, Vincent; Ávila, David; Izquierdo, Jesus G; Rebollar, Esther; Bañares, Luis; Castillejo, Marta; de Nalda, Rebeca; Martin, Margarita

    2016-02-01

    Femtosecond lasers, used as tools to investigate the ablation dynamics of solids, can help to develop strategies to control the deposition of nanomaterials by pulsed laser ablation. In this work, Co/ZnS targets, potential candidates for the synthesis of diluted magnetic semiconductor materials, are irradiated by sequences of two femtosecond laser pulses delayed in the picosecond time scale. The ionic composition of the ablation plasma and the dependence of the ion signals on the interpulse delay and relative fluence are determined by time-of-flight mass spectrometry. The results show that, when pulses of different fluence are used, highly asymmetric ion yields are obtained, with more intense ion signals detected when the lower fluence pulse is temporally ahead. The comparison between asymmetric and equal fluence double pulse ablation dynamics provides some understanding of the different processes that modify the properties of the layer irradiated by the first pulse and of the mechanisms affecting the coupling of the delayed pulse into the material. The final outcome of the double pulse irradiation is characterized through the analysis of the deposits produced upon ablation. PMID:26751831

  5. Wall ablation, gas dynamics, and the history of wall stresses in ICF target chambers

    SciTech Connect

    Orth, C.D. )

    1989-09-30

    We calculate the history of wall stresses for spherical aluminum LMF-type ICF target chambers 10 cm thick with 1400-MJ pellets using a simple computer program called CHAMBER that incorporates the physics of first-wall ablation and chamber gas dynamics, including dissociation, ionization, and gas reverberations. By considering the time dependence of the wall stresses, we calculate peak stresses that are higher or lower than previous estimates based on the dynamic formula {sigma}{sub dyn} {approx}Pr/{Delta}R, depending on the radius of the chamber. Here P is the interior pressure, R is the chamber radius, and {Delta}R is the wall thickness. In particular, the previous estimates are too small for chambers with radii R > 4 m or R < 0.5 m, because the ablation impulse dominates the stress for R > 4 m, and the post-ablation pressure impulse dominates for R < 0.5 cm. CHAMER also shows that considerably more wall mass can be ablated after the x-ray-vaporized mass fills the chamber if the thermalized vapor radiates more energy to the wall than the wall can conduct away by heat condition, as in small chambers. Venting of a chamber can reduce the wall stress only to that caused by the ablation impulse, and only for vents with radii comparable to the radius of the chamber. 1 ref., 2 figs.

  6. Dynamics of Femtosecond Laser Ablation Plume Studied With Ultrafast X-ray Absorption Fine Structure Imaging

    SciTech Connect

    Oguri, Katsuya; Okano, Yasuaki; Nishikawa, Tadashi; Nakano, Hidetoshi

    2010-10-08

    We investigated the dynamic process of an expanding femtosecond laser ablation plume of aluminum generated in an irradiation intensity range of 10{sup 13}-10{sup 15} W/cm{sup 2} with the ultrafast x-ray absorption fine structure (XAFS) imaging technique. The XAFS spectra of the aluminum L{sub II,III} edge of the plume revealed that the plume consists of doubly and singly charged ions, neutral atoms, liquid particles, and possible atomic clusters. Scanning electron microscopy of deposited ablation particles confirmed that the liquid particles corresponds to the spherical nanoparticles with a size ranging from several tens nanometers to approximately 200 nm. The spatiotemporal evolution of the XAFS image of the plume shows the sequential appearance of each ablation particle from aluminum surface according to its ejection velocity. The result suggests that the photomechanical fragmentation process, which was theoretically proposed, is dominant mechanism for the nanoparticle ejection under the irradiation intensity far from the ablation threshold of aluminum. This study clearly demonstrates the potential of our technique for measuring the ultrafast dynamics of femtosecond laser ablation process.

  7. X-ray ablation measurements and modeling for ICF applications

    SciTech Connect

    Anderson, A.T.

    1996-09-01

    X-ray ablation of material from the first wall and other components of an ICF (Inertial Confinement Fusion) chamber is a major threat to the laser final optics. Material condensing on these optics after a shot may cause damage with subsequent laser shots. To ensure the successful operation of the ICF facility, removal rates must be predicted accurately. The goal for this dissertation is to develop an experimentally validated x-ray response model, with particular application to the National Ignition Facility (NIF). Accurate knowledge of the x-ray and debris emissions from ICF targets is a critical first step in the process of predicting the performance of the target chamber system. A number of 1-D numerical simulations of NIF targets have been run to characterize target output in terms of energy, angular distribution, spectrum, and pulse shape. Scaling of output characteristics with variations of both target yield and hohlraum wall thickness are also described. Experiments have been conducted at the Nova laser on the effects of relevant x-ray fluences on various materials. The response was diagnosed using post-shot examinations of the surfaces with scanning electron microscope and atomic force microscope instruments. Judgments were made about the dominant removal mechanisms for each material. Measurements of removal depths were made to provide data for the modeling. The finite difference ablation code developed here (ABLATOR) combines the thermomechanical response of materials to x-rays with models of various removal mechanisms. The former aspect refers to energy deposition in such small characteristic depths ({approx} micron) that thermal conduction and hydrodynamic motion are significant effects on the nanosecond time scale. The material removal models use the resulting time histories of temperature and pressure-profiles, along with ancillary local conditions, to predict rates of surface vaporization and the onset of conditions that would lead to spallation.

  8. HIFU Therapy Compared with Other Thermal Ablation Methods in a Perfused Organ Model

    NASA Astrophysics Data System (ADS)

    Jenne, Jürgen W.; Risse, Frank; Häcker, Axel; Peters, Kristina; Siegler, Peter; Divkovic, Gabriela Wilzbach; Huber, Peter E.

    2007-05-01

    Therapy with high intensity focused ultrasound (HIFU) has been shown to be both safe and clinically practical in a growing number of patient studies for a variety of different target organs. Especially in cancer therapy there are comparable ablation methods like radio frequency (RFA) or laser (LITT) ablation, which are clinically more accepted. In an ongoing study we compare HIFU with RF- and laser ablation under MRI guidance in a perfused organ model. All evaluated techniques were appropriate to induce defined and localized ablation necrosis in the renal cortex. Our HIFU system and the laser system were completely MRI compatible. The tested RF- system showed local needle artefacts and disturbed the MR images during operation. The ablation rate of HIFU using a spot scanning technique was clearly lower compared to the other ablation techniques. However, advanced HIFU scanning methods might overcome this limitation. In addition HIFU is the only complete non-invasive ablation technique.

  9. Planar laser-driven ablation model for nonlocalized absorption

    SciTech Connect

    Dahmani, F.; Kerdja, T. )

    1991-05-01

    A model for planar laser-driven ablation is presented. Nonlocalized inverse bremsstrahlung absorption of laser energy at a density {ital n}{sub 1}{lt}{ital n}{sub {ital c}} is assumed. A steady-state solution in the conduction zone is joined to a rarefaction wave in the underdense plasma. The calculations relate all steady-state fluid quantities to only the material, absorbed intensity, and laser wavelength. The theory agrees well with results from a computer hydrodynamics code MEDUSA (Comput. Phys. Commun. {bold 7}, 271 (1974)) and experiments.

  10. Dynamic in situ measurement of ablation rate in a composite rocket nozzle

    NASA Astrophysics Data System (ADS)

    Dean, Peter D.; Subbarao, E. R.; Smith, Marian

    1990-01-01

    This paper describes the development and calibration of an acoustic probe for dynamic in situ measurements of ablation rate in a composite rocket nozzle. The probe, which is to be inserted radially into the nozzle, is designed so that its end melts as the nozzle ablates. An ultrasonic transducer is used to launch an acoustic wave in the probe, and the length of the remaining probe is determined by analyzing the reflected pulses. The paper describes the probe test equipment, the criteria for material selection, the preliminary tests, and the analysis methodology. Results of experimental tests are presented.

  11. Improved model for the angular dependence of excimer laser ablation rates in polymer materials

    SciTech Connect

    Pedder, J. E. A.; Holmes, A. S.; Dyer, P. E.

    2009-10-26

    Measurements of the angle-dependent ablation rates of polymers that have applications in microdevice fabrication are reported. A simple model based on Beer's law, including plume absorption, is shown to give good agreement with the experimental findings for polycarbonate and SU8, ablated using the 193 and 248 nm excimer lasers, respectively. The modeling forms a useful tool for designing masks needed to fabricate complex surface relief by ablation.

  12. Electron dynamics and prompt ablation of aluminum surface excited by intense femtosecond laser pulse

    NASA Astrophysics Data System (ADS)

    Ionin, A. A.; Kudryashov, S. I.; Makarov, S. V.; Seleznev, L. V.; Sinitsyn, D. V.

    2014-12-01

    Thin aluminum film homogeneously heated by intense IR femtosecond laser pulses exhibits on the excitation timescale consequent fluence-dependent rise and drop of the IR-pump self-reflectivity, followed by its final saturation at higher fluences F > 0.3 J/cm2. This prompt optical dynamics correlates with the initial monotonic increase in the accompanying laser-induced electron emission, which is succeeded by its non-linear (three-photon) increase for F > 0.3 J/cm2. The underlying electronic dynamics is related to the initial saturation of IR resonant interband transitions in this material, followed by its strong instantaneous electronic heating via intraband transitions during the pump pulse resulting in thermionic emission. Above the threshold fluence of 0.3 J/cm2, the surface electronic heating is balanced during the pump pulse by simultaneous cooling via intense plasma removal (prompt ablation). The relationship between the deposited volume energy density in the film and its prompt electronic temperature derived from the self-reflection measurements using a Drude model, demonstrates a kind of electron "liquid-vapor" phase transition, driven by strong cubic optical non-linearity of the photo-excited aluminum.

  13. Dynamics of plasma expansion and shockwave formation in femtosecond laser-ablated aluminum plumes in argon gas at atmospheric pressures

    SciTech Connect

    Miloshevsky, Alexander; Harilal, Sivanandan S.; Miloshevsky, Gennady Hassanein, Ahmed

    2014-04-15

    Plasma expansion with shockwave formation during laser ablation of materials in a background gasses is a complex process. The spatial and temporal evolution of pressure, temperature, density, and velocity fields is needed for its complete understanding. We have studied the expansion of femtosecond (fs) laser-ablated aluminum (Al) plumes in Argon (Ar) gas at 0.5 and 1 atmosphere (atm). The expansion of the plume is investigated experimentally using shadowgraphy and fast-gated imaging. The computational fluid dynamics (CFD) modeling is also carried out. The position of the shock front measured by shadowgraphy and fast-gated imaging is then compared to that obtained from the CFD modeling. The results from the three methods are found to be in good agreement, especially during the initial stage of plasma expansion. The computed time- and space-resolved fields of gas-dynamic parameters have provided valuable insights into the dynamics of plasma expansion and shockwave formation in fs-pulse ablated Al plumes in Ar gas at 0.5 and 1 atm. These results are compared to our previous data on nanosecond (ns) laser ablation of Al [S. S. Harilal et al., Phys. Plasmas 19, 083504 (2012)]. It is observed that both fs and ns plumes acquire a nearly spherical shape at the end of expansion in Ar gas at 1 atm. However, due to significantly lower pulse energy of the fs laser (5 mJ) compared to pulse energy of the ns laser (100 mJ) used in our studies, the values of pressure, temperature, mass density, and velocity are found to be smaller in the fs laser plume, and their time evolution occurs much faster on the same time scale. The oscillatory shock waves clearly visible in the ns plume are not observed in the internal region of the fs plume. These experimental and computational results provide a quantitative understanding of plasma expansion and shockwave formation in fs-pulse and ns-pulse laser ablated Al plumes in an ambient gas at atmospheric pressures.

  14. Modeling nanoparticle formation by laser ablation and by spark discharges

    NASA Astrophysics Data System (ADS)

    Itina, Tatiana E.

    2016-03-01

    Nanoparticles have found numerous applications in such areas as photonics, electronics, medicine, etc. Further development of these fields requires reliable and versatile methods of nanoparticle synthesis with well-controlled properties. Among promising synthesis techniques, both laser ablation and plasma discharges are considered. These methods provide numerous advantages that are unique in several cases. On one hand, the main advantage of the laser ablation method is in the possibilities of changing laser parameters and background conditions and in its capacity to preserve stoichiometry. Laser-based methods also yield bio-compatible nanoparticles and nano-colloids with unique chemical properties. Laser-induced fragmentation provides additional control ways over nanoparticle sizes. To better understand and to optimize these processes, detailed numerical modeling is performed. The involved stages are considered and analyzed. The resulting nanoparticle parameters are investigated as a function of the experimental conditions. Nanoparticle properties, such as mean size and mean concentration are analyzed. Differences and similarities between the considered synthesis methods are discussed.

  15. Modeling and Simulation of Ablation-Controlled Plasmas

    NASA Astrophysics Data System (ADS)

    Kundrapu, Madhusudhan N.

    Ablation and plasma formation in high energy laser target interactions and arc discharges are studied numerically. Each of the two processes is modeled separately due to the type of energy source and the resulting flow eld. Ablation of the target material and plasma formation are coupled to obtain evaporation rate, temperature distribution, velocity eld, and species concentration self-consistently. Laser ablation is studied in the perspective of directed energy applications, where beam size varies from few centimeters to tens of centimeters with energies extending up to 10 kW/cm2. Because of this high energy deposition, the evaporated material expands to supersonic speeds into the free space. Due to the large spot sizes and associated supersonic flow, one dimensional Euler equations are considered to be sufficient for modeling the plume. Instead, more emphasis was given to evaporation model, by introducing Knudsen layer kinetics at the plume target interface, and plasma shielding. The evaporation rate is validated with results from the experiments and simulations are carried out to nd the in fluence of laser beam frequency on evaporation rates. The evaporation model used in this work is found to be more accurate than the widely used model based on sonic speed assumption. The optimum beam wavelength for Al surfaces is found to be 850 nm. Attenuation of telemetry data by plasma is a concern for the testing of directed energy systems. Electrostatic approach for the mitigation of communication attenuation is analyzed to obtain the fluency limits up to which the approach can be implemented. It is found from sheath calculations that uninterrupted telemetry can be achieved through Al plasma for fluences below 4 J/cm2 at a background pressure of 1 atm, using a maximum bias voltage of 10 kV . Arc discharge ablation is modeled for the synthesis of nanoparticles. The electric arc generated between the electrodes, placed inside a Helium chamber, evaporates the catalyst

  16. Gas-dynamic acceleration of laser-ablation plumes: Hyperthermal particle energies under thermal vaporization

    SciTech Connect

    Morozov, A. A.; Evtushenko, A. B.; Bulgakov, A. V.

    2015-02-02

    The expansion of a plume produced by low-fluence laser ablation of graphite in vacuum is investigated experimentally and by direct Monte Carlo simulations in an attempt to explain hyperthermal particle energies for thermally vaporized materials. We demonstrate that the translation energy of neutral particles, ∼2 times higher than classical expectations, is due to two effects, hydrodynamic plume acceleration into the forward direction and kinetic selection of fast particles in the on-axis region. Both effects depend on the collision number within the plume and on the particles internal degrees of freedom. The simulations allow ablation properties to be evaluated, such as ablation rate and surface temperature, based on time-of-flight measurements. Available experimental data on kinetic energies of various laser-produced particles are well described by the presented model.

  17. Hydrodynamic model for ultra-short pulse ablation of hard dental tissue

    SciTech Connect

    London, R.A.; Bailey, D.S.; Young, D.A.; Alley, W.E.; Feit, M.D.; Rubenchik, A.M.; Neev, J.

    1996-02-29

    A computational model for the ablation of tooth enamel by ultra-short laser pulses is presented. The role of simulations using this model in designing and understanding laser drilling systems is discussed. Pulses of duration 300 fsec and intensity greater than 10{sup 12} W/cm{sup 2} are considered. Laser absorption proceeds via multi-photon initiated plasma mechanism. The hydrodynamic response is calculated with a finite difference method, using an equation of state constructed from thermodynamic functions including electronic, ion motion, and chemical binding terms. Results for the ablation efficiency are presented. An analytic model describing the ablation threshold and ablation depth is presented. Thermal coupling to the remaining tissue and long-time thermal conduction are calculated. Simulation results are compared to experimental measurements of the ablation efficiency. Desired improvements in the model are presented.

  18. Experimental measurement of ablation effects in plasma armature railguns

    SciTech Connect

    Parker, J.V.; Parsons, W.M.

    1986-01-01

    Experimental evidence supporting the importance of ablation in plasma armature railguns is presented. Experiments conducted using the HYVAX and MIDI-2 railguns are described. Several indirect effects of ablation are identified from the experimental results. An improved ablation model of plasma armature dynamics is proposed which incorporates the restrike process.

  19. Higher Order Chemistry Models in the CFD Simulation of Laser-Ablated Carbon Plumes

    NASA Technical Reports Server (NTRS)

    Scott, C. D.; Greendyke, R. B.; Creel, J. R.; Payne, B. T.

    2005-01-01

    Production of single-walled carbon nanotubes (SWNT) has taken place for a number of years and by a variety of methods such-as laser ablation, chemical vapor deposition, and arc-jet ablation. Yet, little is actually understood about the exact chemical kinetics and processes that occur in SWNT formation. In recent time, NASA Johnson Space Center has devoted a considerable effort to the experimental evaluation of the laser ablation production process for SWNT originally developed at Rice University. To fully understand the nature of the laser ablation process it is necessary to understand the development of the carbon plume dynamics within the laser ablation oven. The present work is a continuation of previous studies into the efforts to model plume dynamics using computational fluid dynamics (CFD). The ultimate goal of the work is to improve understanding of the laser ablation process, and through that improved understanding, refine the laser ablation production of SWNT. Fig. 1 shows a basic schematic of the laser-ablation oven at NASA-JSC. Construction of the facility is simple in concept. Two concentric quartz tubes of 1.5 mm thickness form the inner and outer tubes with inside diameters of 2.2 and 5.08 cm respectively. At one end of the inner tube are located two 60 Hz pulsed lasers operating at 1064 nm and 532 nm wavelength with beam diameters of 5 mm aligned coaxially with the longitudinal axis of the inner quartz tube. For standard nanotube production runs, a 10 ns 532 nm pulse is followed 50 ns later by a 10 ns 1064 nm pulse. Each pulse is of 300 mJ energy. A target of carbon graphite with approximately 1% nickel and cobalt catalysts is located at the other end of the inner quartz tube. In the ordinary processing of SWNT, a base flow of 100 sccm of argon is maintained from the laser location and exits past the carbon target at a pressure of 66.7 kPa. These conditions yield a baseline mass flow through the chamber of 2.723x10(exp -6)kg/s of argon. The whole

  20. Femtosecond laser ablation dynamics of fused silica extracted from oscillation of time-resolved reflectivity

    SciTech Connect

    Kumada, Takayuki Akagi, Hiroshi; Itakura, Ryuji; Otobe, Tomohito; Yokoyama, Atsushi

    2014-03-14

    Femtosecond laser ablation dynamics of fused silica is examined via time-resolved reflectivity measurements. After optical breakdown was caused by irradiation of a pump pulse with fluence F{sub pump} = 3.3–14.9 J/cm{sup 2}, the reflectivity oscillated with a period of 63 ± 2 ps for a wavelength λ = 795 nm. The period was reduced by half for λ = 398 nm. We ascribe the oscillation to the interference between the probe pulses reflected from the front and rear surfaces of the photo-excited molten fused silica layer. The time-resolved reflectivity agrees closely with a model comprising a photo-excited layer which expands due to the formation of voids, and then separates into two parts, one of which is left on the sample surface and the other separated as a molten thin layer from the surface by the spallation mechanism. Such oscillations were not observed in the reflectivity of soda-lime glass. Whether the reflectivity oscillates or not probably depends on the layer viscosity while in a molten state. Since viscosity of the molten fused silica is several orders of magnitude higher than that of the soda-lime glass at the same temperature, fused silica forms a molten thin layer that reflects the probe pulse, whereas the soda-lime glass is fragmented into clusters.

  1. Numerical models to evaluate the temperature increase induced by ex vivo microwave thermal ablation.

    PubMed

    Cavagnaro, M; Pinto, R; Lopresto, V

    2015-04-21

    Microwave thermal ablation (MTA) therapies exploit the local absorption of an electromagnetic field at microwave (MW) frequencies to destroy unhealthy tissue, by way of a very high temperature increase (about 60 °C or higher). To develop reliable interventional protocols, numerical tools able to correctly foresee the temperature increase obtained in the tissue would be very useful. In this work, different numerical models of the dielectric and thermal property changes with temperature were investigated, looking at the simulated temperature increments and at the size of the achievable zone of ablation. To assess the numerical data, measurement of the temperature increases close to a MTA antenna were performed in correspondence with the antenna feed-point and the antenna cooling system, for increasing values of the radiated power. Results show that models not including the changes of the dielectric and thermal properties can be used only for very low values of the power radiated by the antenna, whereas a good agreement with the experimental values can be obtained up to 20 W if water vaporization is included in the numerical model. Finally, for higher power values, a simulation that dynamically includes the tissue's dielectric and thermal property changes with the temperature should be performed.

  2. Ablation dynamics in wire array Z-pinches under modifications on global magnetic field topology

    SciTech Connect

    Veloso, Felipe Muñoz-Cordovez, Gonzalo; Donoso-Tapia, Luis; Valenzuela-Villaseca, Vicente; Favre, Mario; Wyndham, Edmund; Suzuki-Vidal, Francisco; Swadling, George; Chittenden, Jeremy

    2015-07-15

    The dynamics of ablation streams and precursor plasma in cylindrical wire array Z-pinches under temporal variations of the global magnetic field topology is investigated through experiments and numerical simulations. The wire arrays in these experiments are modified by replacing a pair of consecutive wires with wires of a larger diameter. This modification leads to two separate effects, both of which impact the dynamics of the precursor plasma; firstly, current is unevenly distributed between the wires and secondly, the thicker wires take longer to fully ablate. The uneven distribution of current is evidenced in the experiments by the drift of the precursor off axis due to a variation in the global magnetic field topology which modifies the direction of the ablation streams tracking the precursor position. The variation of the global magnetic field due to the presence of thick wires is studied with three-dimensional magnetohydrodynamic (MHD) simulations, showing that the global field changes from the expected toroidal field to a temporally variable topology after breakages appear in the thin wires. This leads to an observed acceleration of the precursor column towards the region closer to the thick wires and later, when thick wires also present breakages, it continues moving away from the original array position as a complicated and disperse object subject to MHD instabilities.

  3. Modeling Ablation of Fibrous Materials from Bulk to Knudsen Regime

    NASA Technical Reports Server (NTRS)

    Lachaud, Jean; Mansour, Nagi N.

    2008-01-01

    Material-environment interactions are analyzed at microscopic scale to explain the lower than expected density observed by post-flight analysis of the char layer on the Stardust shield. Mass transfer, ablation (oxidation), and surface recession of fibrous material is simulated in 3D using a Monte-Carlo simulation tool. Ablation is found to occur either at the surface or in volume depending on Knudsen and Thiele number values. This study supports the idea of volume ablation followed by possible carbon fiber spallation that may explain post-flight analyses.

  4. Early plume and shock wave dynamics in atmospheric-pressure ultraviolet-laser ablation of different matrix-assisted laser ablation matrices

    SciTech Connect

    Schmitz, Thomas A.; Koch, Joachim; Guenther, Detlef; Zenobi, Renato

    2011-06-15

    Pulsed laser ablation of molecular solids is important for identification and quantification in (bio-)organic mass spectrometry, for example using matrix-assisted laser desorption/ionization (MALDI). Recently, there has been a major shift to using MALDI and related laser ablation/post-ionization methods at atmospheric pressure. However, the underlying laser ablation processes, in particular early plume formation and expansion, are still poorly understood. Here, we present a study of the early ablation processes on the ns-time scale in atmospheric pressure UV-laser ablation of anthracene as well as of different common MALDI matrices such as 2,5-dihydroxybenzoic acid (2,5-DHB), {alpha}-cyano-4-hydroxycinnamic acid and sinapinic acid. Material release as well as the formation and expansion of hemi-spherical shock waves were studied by shadowgraphy with high temporal resolution ({approx}5 ns). The applicability of the classical Taylor-Sedov model for expansion of strong shock waves ('point-blast model'), as well as the drag force model, were evaluated to mathematically describe the observed shock wave propagation. The time- and energy-dependent expansion of the shock waves could be described using a Taylor-Sedov scaling law of the form R {proportional_to} t{sup q}, when a q-exponent of {approx}0.5 instead of the theoretical value of q 0.4 was found, indicating a faster expansion than expected. The deviations from the ideal value of q were attributed to the non-negligible influence of ambient pressure, a weak versus strong shock regime, and additional acceleration processes present in laser ablation that surpass the limit of the point-blast model. The onset of shock wave formation at a fluence of {approx}15-30 mJ/cm{sup 2} for the compounds investigated coincides with the onset of bulk material release, whereas, pure desorption below this fluence threshold did not lead to features visible in shadowgraphy.

  5. Electrophysiological Rotor Ablation in In-Silico Modeling of Atrial Fibrillation: Comparisons with Dominant Frequency, Shannon Entropy, and Phase Singularity

    PubMed Central

    Hwang, Minki; Song, Jun-Seop; Lee, Young-Seon; Li, Changyong; Shim, Eun Bo; Pak, Hui-Nam

    2016-01-01

    Background Although rotors have been considered among the drivers of atrial fibrillation (AF), the rotor definition is inconsistent. We evaluated the nature of rotors in 2D and 3D in- silico models of persistent AF (PeAF) by analyzing phase singularity (PS), dominant frequency (DF), Shannon entropy (ShEn), and complex fractionated atrial electrogram cycle length (CFAE-CL) and their ablation. Methods Mother rotor was spatiotemporally defined as stationary reentries with a meandering tip remaining within half the wavelength and lasting longer than 5 s. We generated 2D- and 3D-maps of the PS, DF, ShEn, and CFAE-CL during AF. The spatial correlations and ablation outcomes targeting each parameter were analyzed. Results 1. In the 2D PeAF model, we observed a mother rotor that matched relatively well with DF (>9 Hz, 71.0%, p<0.001), ShEn (upper 2.5%, 33.2%, p<0.001), and CFAE-CL (lower 2.5%, 23.7%, p<0.001). 2. The 3D-PeAF model also showed mother rotors that had spatial correlations with DF (>5.5 Hz, 39.7%, p<0.001), ShEn (upper 8.5%, 15.1%, p <0.001), and CFAE (lower 8.5%, 8.0%, p = 0.002). 3. In both the 2D and 3D models, virtual ablation targeting the upper 5% of the DF terminated AF within 20 s, but not the ablations based on long-lasting PS, high ShEn area, or lower CFAE-CL area. Conclusion Mother rotors were observed in both 2D and 3D human AF models. Rotor locations were well represented by DF, and their virtual ablation altered wave dynamics and terminated AF. PMID:26909492

  6. Multiscale Modeling of Ablation and Pyrolysis in PICA-Like materials

    NASA Technical Reports Server (NTRS)

    Lachaud, Jean; Mansour, Nagi N.

    2008-01-01

    During atmospheric entry of planetary probes, the thermal protection system (TIPS) of the probe is exposed to high temperatures under low pressures. In these conditions, carbonous fibrous TIPS materials may undergo oxidation leading to mass loss and wall recession called ablation. This work aims to improve the understanding of material/environment interactions through a study of the coupling between oxygen transport in the Knudsen regime, heterogeneous oxidation of carbon, and surface recession. A 3D Random Walk Monte Carlo simulation tool is used for this study. The fibrous architecture of a model material, consisting of high porosity random array of carbon fibers, is numerically represented on a 3D Cartesian grid. Mass transport in the Knudsen regime from the boundary layer to the surface, and inside this porous material is simulated by random walk. A reaction probability is used to simulate the heterogeneous oxidation reaction. The surface recession of the fibers is followed by front tracking using a simplified marching cube approach. The output data of the simulations are ablation velocity and dynamic evolution of the material porosity. A parametric study is carried out to analyze the material behavior as a function of Knudsen number for the porous media (length of the mean free path compared to the mean pore diameter) and the intrinsic reactivity of the carbon fibers. The model is applied to Stardust mission reentry conditions and explains the unexpected behavior of the TIPS material that underwent mass loss in volume.

  7. Non-ablative hyperthermic mesenchymal regeneration: a proposed mechanism of action based on the Vivev model

    NASA Astrophysics Data System (ADS)

    Vos, Jeffrey A.; Livengood, Ryan H.; Jessop, Morris; Coad, James E.

    2011-03-01

    Novel non-ablative hyperthermic medical devices are currently being developed, in association with cryogen surface cooling, to rejuvenate tissues without collagen scarring. These devices have been designed to remodel skin, manage urinary stress incontinence, and more recently, treat vaginal laxity. In contrast to the thermal injury and reparative healing associated with higher energy ablation systems, these lower energy non-ablative systems are designed to subtly modify the collagen, stimulate the fibroblasts, and maintain a functional tissue architecture that subsequently promotes tissue rejuvenation and restoration. While these devices have primarily relied on clinical outcome questionnaires and satisfaction surveys to establish efficacy, a physiologic explanation for the induced tissue changes and tightening has not been well documented. Recent histology studies, using the Viveve ovine vaginal treatment model, have identified changes that propose both a mechanism of action and a tissue remodeling timeline for such non-ablative hyperthermic devices. The Viveve model results are consistent with subtle connective tissue changes leading to fibroblast stimulation and subsequent collagen replacement and augmentation. Unlike tissue ablation devices that cause thermal necrosis, these non-ablative devices renew the targeted tissue without dense collagenous scarring over a period of 3 or more months. The spectrum of histologic findings, as illustrated in the Viveve ovine vaginal model, further support the previously documented safety and efficacy profiles for low-dose non-ablative hyperthermic devices that rejuvenate and tighten submucosal tissues.

  8. Multidiagnostics analysis of ion dynamics in ultrafast laser ablation of metals over a large fluence range

    SciTech Connect

    Anoop, K. K.; Polek, M. P.; Bruzzese, R.; Amoruso, S.; Harilal, Sivanandan S.

    2015-02-28

    The ions dynamics in ultrafast laser ablation of metals is studied over a fluence range spanning from the ablation threshold up to ~75 J/cm2 by means of three established diagnostic techniques. Langmuir probe, Faraday cup and spectrally resolved ICCD imaging simultaneously monitor the laser-produced plasma ions produced during ultrafast laser ablation of a copper target. The fluence dependence of ion yield is analyzed observing the occurrence of three different regimes. Moreover, the specific ion yield shows a maximum at about 4-5 J/cm2, followed by a gradual reduction and a transition to a high-fluence regime above ~50 J/cm2. The fluence variation of the copper ions angular distribution is also analyzed, observing a gradual increase of forward peaking of Cu ions for fluences up to ~10 J/cm2. Then, a broader ion component is observed at larger angles for fluences larger than ~10 J/cm2. Finally, an experimental characterization of the ions angular distribution for several metallic targets (Mg, Al, Cr, Fe, Cu, and W) is carried out at a relatively high fluence of ~66 J/cm2. Interestingly, the ion emission from the volatile metals show a narrow forward peaked distribution and a high peak ion yield compared to the refractory metals. Moreover, the width of ion angular distributions presents a striking correlation with the peak ion yield.

  9. Optimization of Catheter Ablation of Atrial Fibrillation: Insights Gained from Clinically-Derived Computer Models

    PubMed Central

    Zhao, Jichao; Kharche, Sanjay R.; Hansen, Brian J.; Csepe, Thomas A.; Wang, Yufeng; Stiles, Martin K.; Fedorov, Vadim V.

    2015-01-01

    Atrial fibrillation (AF) is the most common heart rhythm disturbance, and its treatment is an increasing economic burden on the health care system. Despite recent intense clinical, experimental and basic research activity, the treatment of AF with current antiarrhythmic drugs and catheter/surgical therapies remains limited. Radiofrequency catheter ablation (RFCA) is widely used to treat patients with AF. Current clinical ablation strategies are largely based on atrial anatomy and/or substrate detected using different approaches, and they vary from one clinical center to another. The nature of clinical ablation leads to ambiguity regarding the optimal patient personalization of the therapy partly due to the fact that each empirical configuration of ablation lines made in a patient is irreversible during one ablation procedure. To investigate optimized ablation lesion line sets, in silico experimentation is an ideal solution. 3D computer models give us a unique advantage to plan and assess the effectiveness of different ablation strategies before and during RFCA. Reliability of in silico assessment is ensured by inclusion of accurate 3D atrial geometry, realistic fiber orientation, accurate fibrosis distribution and cellular kinetics; however, most of this detailed information in the current computer models is extrapolated from animal models and not from the human heart. The predictive power of computer models will increase as they are validated with human experimental and clinical data. To make the most from a computer model, one needs to develop 3D computer models based on the same functionally and structurally mapped intact human atria with high spatial resolution. The purpose of this review paper is to summarize recent developments in clinically-derived computer models and the clinical insights they provide for catheter ablation. PMID:25984605

  10. Image-based modeling and characterization of RF ablation lesions in cardiac arrhythmia therapy

    NASA Astrophysics Data System (ADS)

    Linte, Cristian A.; Camp, Jon J.; Rettmann, Maryam E.; Holmes, David R.; Robb, Richard A.

    2013-03-01

    In spite of significant efforts to enhance guidance for catheter navigation, limited research has been conducted to consider the changes that occur in the tissue during ablation as means to provide useful feedback on the progression of therapy delivery. We propose a technique to visualize lesion progression and monitor the effects of the RF energy delivery using a surrogate thermal ablation model. The model incorporates both physical and physiological tissue parameters, and uses heat transfer principles to estimate temperature distribution in the tissue and geometry of the generated lesion in near real time. The ablation model has been calibrated and evaluated using ex vivo beef muscle tissue in a clinically relevant ablation protocol. To validate the model, the predicted temperature distribution was assessed against that measured directly using fiberoptic temperature probes inserted in the tissue. Moreover, the model-predicted lesions were compared to the lesions observed in the post-ablation digital images. Results showed an agreement within 5°C between the model-predicted and experimentally measured tissue temperatures, as well as comparable predicted and observed lesion characteristics and geometry. These results suggest that the proposed technique is capable of providing reasonably accurate and sufficiently fast representations of the created RF ablation lesions, to generate lesion maps in near real time. These maps can be used to guide the placement of successive lesions to ensure continuous and enduring suppression of the arrhythmic pathway.

  11. In Vivo Evaluation of Lung Microwave Ablation in a Porcine Tumor Mimic Model

    SciTech Connect

    Planche, Olivier; Teriitehau, Christophe; Boudabous, Sana; Robinson, Joey Marie; Rao, Pramod; Deschamps, Frederic; Farouil, Geoffroy; Baere, Thierry de

    2013-02-15

    To evaluate the microwave ablation of created tumor mimics in the lung of a large animal model (pigs), with examination of the ablative synergy of multiple antennas. Fifty-six tumor-mimic models of various sizes were created in 15 pigs by using barium-enriched minced collected thigh muscle injected into the lung of the same animal. Tumors were ablated under fluoroscopic guidance by single-antenna and multiple-antenna microwaves. Thirty-five tumor models were treated in 11 pigs with a single antenna at 75 W for 15 min, with 15 measuring 20 mm in diameter, 10 measuring 30 mm, and 10 measuring 40 mm. Mean circularity of the single-antenna ablation zones measured 0.64 {+-} 0.12, with a diameter of 35.7 {+-} 8.7 mm along the axis of the antenna and 32.7 {+-} 12.8 mm perpendicular to the feeding point. Multiple-antenna delivery of 75 W for 15 min caused intraprocedural death of 2 animals; modified protocol to 60 W for 10 min resulted in an ablation zone with a diameter of 43.0 {+-} 7.7 along the axis of the antenna and 54.8 {+-} 8.5 mm perpendicular to the feeding point; circularity was 0.70 {+-} 0.10. A single microwave antenna can create ablation zones large enough to cover lung tumor mimic models of {<=}4 cm with no heat sink effect from vessels of {<=}6 mm. Synergic use of 3 antennas allows ablation of larger volumes than single-antenna or radiofrequency ablation, but great caution must be taken when 3 antennas are used simultaneously in the lung in clinical practice.

  12. Initial Steps Toward a Hydrologic "Watershed" Model for the Ablation Zone of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Cooper, M. G.; Smith, L. C.; Rennermalm, A. K.; Pitcher, L. H.; Overstreet, B. T.; Chu, V. W.; Ryan, J.; Yang, K.

    2015-12-01

    Surface meltwater production on the Greenland Ice Sheet (GrIS) is a well-documented phenomenon but we lack understanding of the physical mechanisms that control the production, transport, and fate of the meltwater. To address this, we present initial steps toward the development of a novel hydrologic model for supraglacial streamflow on the GrIS. Ice ablation and surface meteorology were measured during a 6-day field campaign in a 112 km2 ablation zone of southwest Greenland. We modeled ablation using SnowModel, an energy balance snow- and ice-ablation model. The required model inputs included standard surface meteorology and a digital elevation model (DEM), and the model outputs include all components of the energy balance and surface meltwater production for each grid cell in the ice-sheet watershed. Our next steps toward developing a complete hydrologic model for supraglacial streamflow in the ablation zone of the GrIS include the application of the meltwater-routing model HydroFlow to compare with in-situ measurements of supraglacial river discharge.

  13. Model-based assessment of probe placement criteria in cancer therapy using RF ablation

    NASA Astrophysics Data System (ADS)

    Tanotogono, E. W.; Akasum, G. F.; Suprijanto; Sudirham, J. J.

    2016-03-01

    Radiofrequency ablation has been developed as a minimally-invasive method for cancer therapy. Nevertheless, the unfeasibility of direct observation during ablation process sometimes becomes a challenge for practitioners, particularly those constrained by the absence of a proper monitoring system. Thus, aiming to develop a prudent cancer therapy planning, this research develops a 3D model that enable practitioners to predict the tissue damage resulted by a simulated ablation before a real ablation is executed. The model, developed using finite element method, is made to mimic real human liver tissue by simulating its physical properties as temperature-dependent functions. Three probe placement cases, representing three different approaches, are analysed to study the effect of probe placement configuration on tissue damage formed during a time-dependent ablation process. The three placement cases are surface-perpendicular placement, misaligned placement, and relatively accurate placement. It can be concluded that the accuracy of a probe placement configuration can be assessed by quantifying two major parameters: average tissue damage in the target domain and accumulated damage resulted in complementary tissue domain. Optimum ablation duration can also be determined by considering those parameters.

  14. Multidiagnostic analysis of ion dynamics in ultrafast laser ablation of metals over a large fluence range

    SciTech Connect

    Anoop, K. K. Bruzzese, R.; Amoruso, S.; Polek, M. P.; Harilal, S. S.

    2015-02-28

    The dynamics of ions in ultrafast laser ablation of metals is studied over fluences ranging from the ablation threshold up to ≈75 J/cm{sup 2} by means of three well-established diagnostic techniques. Langmuir probe, Faraday cup, and spectrally resolved intensified charge coupled device imaging simultaneously monitored the ions produced during ultrafast laser ablation of a pure copper target with 800 nm, ≈50 fs, Ti: Sapphire laser pulses. The fluence dependence of ion yield is analyzed, resulting in the observance of three different regimes. The specific ion yield shows a maximum at about 4–5 J/cm{sup 2}, followed by a gradual reduction and a transition to a high-fluence regime above ≈50 J/cm{sup 2}. The fluence dependence of the copper ions angular distribution is also analyzed, observing a gradual increase in forward-peaking of Cu ions for fluences up to ≈10 J/cm{sup 2}. A broader ion component is observed at larger angles for fluences larger than ≈10 J/cm{sup 2}. Finally, an experimental characterization of the ionic angular distribution for several metallic targets (Mg, Al, Cr, Fe, Cu, and W) is carried out at a relatively high fluence of ≈66 J/cm{sup 2}. Interestingly, the ion emission from the volatile metals shows a narrow, forward-peaked distribution, and a high peak ion yield compared to the refractory metals. Moreover, the width of ionic angular distributions presents a striking correlation with the peak ion yield.

  15. Comparison of the aerodynamic characteristics of an ablating and nonablating blunted conical body

    NASA Technical Reports Server (NTRS)

    Kruse, R. L.

    1973-01-01

    The influence of ablation on the aerodynamic characteristics of a blunted slender cone was investigated. Plastic models were launched in free flight at ablating conditions. The results were compared with results of similar tests using metal nonablating models. Ablation was found to decrease the dynamic stability and the drag, but had little effect on static stability and lift. The plastic models appeared to experience ablation-induced roll.

  16. Thermo-mechanical laser ablation of soft biological tissue: modeling the micro-explosions

    NASA Astrophysics Data System (ADS)

    Majaron, B.; Plestenjak, P.; Lukač, M.

    Characteristics of thermo-mechanical laser ablation process are investigated using an original numerical model. In contrast with previous models, it is based on a microscopic physical model of the micro-explosion process, which combines thermodynamic behavior of tissue water with elastic response of the solid tissue components. Diffusion of dissipated heat is treated in one dimension, and the amount of thermal damage is assessed using the Arrhenius model of the protein denaturation kinetics. Influence of the pulse fluence and duration on temperature profile development, ablation threshold, and depth of thermal damage is analyzed for the case of Er:YAG laser irradiation of human skin. Influence of mechanical properties on the ablation threshold of soft tissue is predicted theoretically for the first time. In addition, feasibility of deep tissue coagulation with a repetitively pulsed Er:YAG laser is indicated from the model.

  17. Dynamics of laser ablative shock waves from one dimensional periodic structured surfaces

    NASA Astrophysics Data System (ADS)

    Paturi, Prem Kiran; Chelikani, Leela; Pinnoju, Venkateshwarlu; Acrhem Team

    2015-06-01

    Spatio-temporal evolution of Laser ablative shock waves (LASWs) from one dimensional periodic structured surfaces (1D-PSS) of Aluminum is studied using time resolved defocused shadowgraphy technique. LASWs are generated by focusing 7 ns pulses from second harmonic of Nd:YAG (532 nm, 10 Hz) laser on to 1D-PSS with sinusoidal and triangular modulations of varying periodicity. An expanded He-Ne laser (632.8 nm) is used as probe beam for shadowgraphy. Evolution of ablative shock front (SF) with 1.5 ns temporal resolution is used to measure position of the SF, its nature, density and pressure behind the SF. The effect of surface modulation on the LASW and contact front dynamics was compared to those from a flat surface (FS) of Aluminum. SWs from FS and PSS obeyed Taylor's solution for spherical and planar nature, respectively. The velocity of SF from 1D PSS had a twofold increase compared to the FS. This was further enhanced for structures whose periodicity is of the order of excitation wavelength. Variation of SF properties with varying periodicity over a range of 3.3 μm to 0.55 μm has the potential to tailor shockwaves of required parameters. The work is supported by Defence Research and Developement Organization, India through Grants-in-Aid Program. The periodic surfaces were procured with financial support from BRFST project No. NFP-MAT-A12-04.

  18. Dynamics of femtosecond laser absorption of fused silica in the ablation regime

    SciTech Connect

    Lebugle, M. Sanner, N.; Varkentina, N.; Sentis, M.; Utéza, O.

    2014-08-14

    We investigate the ultrafast absorption dynamics of fused silica irradiated by a single 500 fs laser pulse in the context of micromachining applications. A 60-fs-resolution pump-probe experiment that measures the reflectivity and transmissivity of the target under excitation is developed to reveal the evolution of plasma absorption. Above the ablation threshold, an overcritical plasma with highly non-equilibrium conditions is evidenced in a thin layer at the surface. The maximum electron density is reached at a delay of 0.5 ps after the peak of the pump pulse, which is a strong indication of the occurrence of electronic avalanche. The results are further analyzed to determine the actual feedback of the evolution of the optical properties of the material on the pump pulse. We introduce an important new quantity, namely, the duration of absorption of the laser by the created plasma, corresponding to the actual timespan of laser absorption by inverse Bremsstrahlung. Our results indicate an increasing contribution of plasma absorption to the total material absorption upon raising the excitation fluence above the ablation threshold. The role of transient optical properties during the energy deposition stage is characterized and our results emphasize the necessity to take it into account for better understanding and control of femtosecond laser-dielectrics interaction.

  19. Experiments on Dynamic Overpressure Stabilization of Ablative Richtmyer--Meshkov Growth in ICF Targets on OMEGA

    NASA Astrophysics Data System (ADS)

    Gotchev, O. V.; Goncharov, V. N.; Jaanimagi, P. A.; Knauer, J. P.; Meyerhofer, D. D.

    2002-11-01

    Dynamic overpressure sets the growth rate of the ablative Richtmyer--Meshkov (RM) instability and the late-time imprint levels in directly driven ICF targets. It leads to temporal oscillations of the perturbed ablation front, which have been predicted analytically and observed experimentally,(Y. Aglitskiy et al.), Phys. Plasmas 9, 2264 (2002). and in 2-D ORCHID simulations. These predictions were verified on OMEGA by measuring the perturbation amplitudes and frequencies directly with an x-ray framing camera through face-on x-ray radiography. Planar plastic targets with variable thickness (20 to 60 μm) and single-mode (λ = 10 to 30 μm) ripples on the front surface were irradiated with 1.5-ns square UV laser pulses at maximum energy. Results clearly indicate a phase reversal in the evolution of the target areal density perturbations, in good agreement with theory and simulation. Nonlinearity in the evolution of the preimposed mode, resulting in an enriched spectrum, was observed for initial amplitudes previously believed to develop linearly with time. Upcoming experiments with a high-resolution, streaked imager, will allow for the detailed recording of the evolution of the RM instability and the competing stabilization effect. This work was supported by the U.S. DOE Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460.

  20. Toward Online Modeling for Lesion Visualization and Monitoring in Cardiac Ablation Therapy

    PubMed Central

    Linte, Cristian A.; Camp, Jon J.; Holmes, David R.; Rettmann, Maryam E.; Robb, Richard A.

    2015-01-01

    Despite extensive efforts to enhance catheter navigation, limited research has been done to visualize and monitor the tissue lesions created during ablation in the attempt to provide feedback for effective therapy. We propose a technique to visualize the temperature distribution and extent of induced tissue injury via an image-based model that uses physiological tissue parameters and relies on heat transfer principles to characterize lesion progression in near real time. The model was evaluated both numerically and experimentally using ex vivo bovine muscle samples while emulating a clinically relevant ablation protocol. Results show agreement to within 5°C between the model-predicted and experimentally measured end-ablation tissue temperatures, as well as comparable predicted and observed lesion characteristics. The model yields temperature and lesion updates in near real-time, thus providing reasonably accurate and sufficiently fast monitoring for effective therapy. PMID:24505643

  1. Finite element modeling of cooled-tip probe radiofrequency ablation processes in liver tissue.

    PubMed

    Barauskas, Rimantas; Gulbinas, Antanas; Vanagas, Tomas; Barauskas, Giedrius

    2008-06-01

    Finite element model of radiofrequency ablation (RFA) with cooled-tip probe in liver has been developed by employing COMSOL Multiphysics software. It describes coupled electric, thermal and sodium chloride solution infiltration flow phenomena taking place during ablation processes. Features of hydraulic capacity, saturation of the tissue by infiltration, and dependency of electrical conductivity on the damage integral of the tissue have been supplied to the model. RFA experiments have validated the model. Physical parameters describing hydraulic capacity and hydraulic conductivity in the tissue, as well as, the relation of electrical conductivity against the value of damage integral have been determined.

  2. An animal model for learning Nd:YAG laser ablation of the endometrium.

    PubMed

    Gimpelson, R J; Schomburg, M E; Bagby, M L

    1989-07-01

    Gynecologists must have a good model for practice before performing Nd:YAG laser ablation on humans. The New Zealand white rabbit has been used as a teaching model in courses. Knowing the anatomy and technique enables gynecologists to acquire the skill and dexterity needed to perform this useful procedure. PMID:2769653

  3. Imaging the ultrafast Kerr effect, free carrier generation, relaxation and ablation dynamics of Lithium Niobate irradiated with femtosecond laser pulses

    SciTech Connect

    Garcia-Lechuga, Mario Siegel, Jan Hernandez-Rueda, Javier; Solis, Javier

    2014-09-21

    The interaction of high-power single 130 femtosecond (fs) laser pulses with the surface of Lithium Niobate is experimentally investigated in this work. The use of fs-resolution time-resolved microscopy allows us to separately observe the instantaneous optical Kerr effect induced by the pulse and the generation of a free electron plasma. The maximum electron density is reached 550 fs after the peak of the Kerr effect, confirming the presence of a delayed carrier generation mechanism. We have also observed the appearance of transient Newton rings during the ablation process, related to optical interference of the probe beam reflected at the front and back surface of the ablating layer. Finally, we have analyzed the dynamics of the photorefractive effect on a much longer time scale by measuring the evolution of the transmittance of the irradiated area for different fluences below the ablation threshold.

  4. Imaging the ultrafast Kerr effect, free carrier generation, relaxation and ablation dynamics of Lithium Niobate irradiated with femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Garcia-Lechuga, Mario; Siegel, Jan; Hernandez-Rueda, Javier; Solis, Javier

    2014-09-01

    The interaction of high-power single 130 femtosecond (fs) laser pulses with the surface of Lithium Niobate is experimentally investigated in this work. The use of fs-resolution time-resolved microscopy allows us to separately observe the instantaneous optical Kerr effect induced by the pulse and the generation of a free electron plasma. The maximum electron density is reached 550 fs after the peak of the Kerr effect, confirming the presence of a delayed carrier generation mechanism. We have also observed the appearance of transient Newton rings during the ablation process, related to optical interference of the probe beam reflected at the front and back surface of the ablating layer. Finally, we have analyzed the dynamics of the photorefractive effect on a much longer time scale by measuring the evolution of the transmittance of the irradiated area for different fluences below the ablation threshold.

  5. Dynamics of femtosecond laser ablation studied with time-resolved x-ray absorption fine structure imaging

    SciTech Connect

    Oguri, Katsuya; Okano, Yasuaki; Nishikawa, Tadashi; Nakano, Hidetoshi

    2009-04-01

    We studied the dynamics of the femtosecond laser ablation of aluminum in an energy range well above the ablation threshold with the ultrafast time-resolved x-ray-absorption fine structure imaging technique. Analyzing the spectral structures near the L absorption edge that appeared in one-dimensional images of soft-x-ray absorbance, we successfully identified doubly and singly charged ions, neutral atoms, liquid nanoparticles, and possible atomic clusters in the expanding ablation plume. We also clarified that the ejected particles depend strongly on the laser irradiation intensity. The spatiotemporal evolution of the ablation particles allows us to estimate the spatial distribution of atomic density and the ejection velocity of each type of particle. In particular, we discuss the temporal sequence of the particle ejection in the early stages of plume expansion. Our experimental results strongly support the idea that photomechanical fragmentation and vaporization are dominant mechanisms for the production of liquid nanoparticles and neutral atoms, respectively, in femtosecond laser ablation induced in an irradiation intensity range of 10{sup 14}-10{sup 15} W/cm{sup 2}.

  6. Dynamic materials evaluation by confined plasma ablation and laser-generated shocks

    NASA Astrophysics Data System (ADS)

    Paisley, Dennis L.; Swift, D. C.; Forsman, A. C.; Kyrala, George A.; Johnson, Randall P.; Kopp, Roger A.; Hauer, Allan A.; Wark, Justin S.; Loveridge, A.; Allen, A. M.; Kalantar, Daniel H.

    2000-08-01

    Laser-generated shocks can and have been used to study their effects on single crystal materials during shock compression. While a crystal undergoes shock compression and release, the transient x- ray diffraction (TXD) of the Bragg and Laue signals is indicative of the change in the crystal lattice spacing. The lattice spacing directly relates to the strain in the crystal. From the dynamic lattice data, strain, strain rate, and/or phase change in a material may be determined. Confined ablation plasmas can efficiently launch a flyer plate for direct impact on a target material imparting a well-characterized shock input and generate kilobar to megabar pressure pulses over a wide range of pulse duration (= 20 ns). The laser-launched flyer plates are analogous to those launched by gas guns, but the smaller size provides an experimental method not easily accessible by larger gas gun experiments. With lasers, diagnostic equipment can be easily synchronized to study dynamic material parameters, i.e., single crystal shock dynamics, interfacial bond strengths of thin coatings, grain-interfaces, texture, and high strain rates (106 - 109 sec-1).

  7. Quantitative Comparison of a New Ab Initio Micrometeor Ablation Model with an Observationally Verifiable Standard Model

    NASA Astrophysics Data System (ADS)

    Meisel, David D.; Szasz, Csilla; Kero, Johan

    2008-06-01

    The Arecibo UHF radar is able to detect the head-echos of micron-sized meteoroids up to velocities of 75 km/s over a height range of 80 140 km. Because of their small size there are many uncertainties involved in calculating their above atmosphere properties as needed for orbit determination. An ab initio model of meteor ablation has been devised that should work over the mass range 10-16 kg to 10-7 kg, but the faint end of this range cannot be observed by any other method and so direct verification is not possible. On the other hand, the EISCAT UHF radar system detects micrometeors in the high mass part of this range and its observations can be fit to a “standard” ablation model and calibrated to optical observations (Szasz et al. 2007). In this paper, we present a preliminary comparison of the two models, one observationally confirmable. Among the features of the ab initio model that are different from the “standard” model are: (1) uses the experimentally based low pressure vaporization theory of O’Hanlon (A users’s guide to vacuum technology, 2003) for ablation, (2) uses velocity dependent functions fit from experimental data on heat transfer, luminosity and ionization efficiencies measured by Friichtenicht and Becker (NASA Special Publication 319: 53, 1973) for micron sized particles, (3) assumes a density and temperature dependence of the micrometeoroids and ablation product specific heats, (4) assumes a density and size dependent value for the thermal emissivity and (5) uses a unified synthesis of experimental data for the most important meteoroid elements and their oxides through least square fits (as functions of temperature, density, and/or melting point) of the tables of thermodynamic parameters given in Weast (CRC Handbook of Physics and Chemistry, 1984), Gray (American Institute of Physics Handbook, 1972), and Cox (Allen’s Astrophysical Quantities 2000). This utilization of mostly experimentally determined data is the main reason for

  8. Alpine proglacial suspended sediment dynamics in warm and cool ablation seasons: Implications for global warming

    NASA Astrophysics Data System (ADS)

    Stott, Tim; Mount, Nick

    2007-01-01

    SummaryData on suspended sediment dynamics and loads obtained from the Torrent du Glacier Noir, Ecrins Massif, SE France, during the unusually warm 2003 and cooler 2004 ablation seasons are used to indicate the likely future impacts of climate warming on suspended sediment transport processes in temperate Alpine proglacial zones. Suspended sediment concentration (SSC) and discharge ( Q) were continuously monitored for 16-day periods during July 2003 and July 2004. SSC was monitored by automated pump sampling during diurnal events in each season and supplemented by a 10 min turbidity record. Q was monitored at a range of flows and a rating curve used to convert a 10 min water level record into Q. Air temperature (AT) was also logged at 10 min intervals throughout the study. Comparison of the 2003 and 2004 monitoring periods showed that daily mean AT measured at the site was 1.2 °C higher in 2003, mean Q was 2.3 times higher, and the suspended sediment load (SSL) was between 3.1 and 4.1 times greater in July 2003 than for the same period in the 2004 ablation season. There is an increase in SSC during the 2004 observation period which is less apparent in 2003, most likely because higher ATs and consequently higher Q earlier in the 2003 melt season had removed available sediment before the study took place in July. The rating curve method for estimating SSL produced a total load for the 16-day study period in 2003 which, when corrected upwards to account for statistical bias, was 10 314 ± 743 t or 95% of the load estimated from the turbidity record for the same period. In 2004 the corrected SSC- Q rating curve estimate was 2504 ± 126 t while the estimate from the turbidity record was 743 ± 112 t though a more sensitive turbidity sensor produced a higher estimate of 3474 ± 302 t. While the different SSL estimation methods in 2004 are not in perfect agreement, the contrast between the two seasons is nevertheless very clear, and is largely attributed to a mean

  9. Dynamics of ions produced by laser ablation of several metals at 193 nm

    SciTech Connect

    Baraldi, G.; Perea, A.; Afonso, C. N.

    2011-02-15

    This work reports the study of ion dynamics produced by ablation of Al, Cu, Ag, Au, and Bi targets using nanosecond laser pulses at 193 nm as a function of the laser fluence from threshold up to 15 J cm{sup -2}. An electrical (Langmuir) probe has been used for determining the ion yield as well as kinetic energy distributions. The results clearly evidence that ablation of Al shows unique features when compared to other metals. The ion yield both at threshold (except for Al, which shows a two-threshold-like behavior) and for a fixed fluence above threshold scale approximately with melting temperature of the metal. Comparison of the magnitude of the yield reported in literature using other wavelengths allows us to conclude its dependence with wavelength is not significant. The evolution of the ion yield with fluence becomes slower for fluences above 4-5 J cm{sup -2} with no indication of saturation suggesting that ionization processes in the plasma are still active up to 15 J cm{sup -2} and production of multiple-charged ions are promoted. This dependence is mirrored in the proportion of ions with kinetic energies higher than 200 eV. This proportion is not significant around threshold fluence for all metals except for Al, which is already 20%. The unique features of Al are discussed in terms of the energy of laser photons (6.4 eV) that is enough to induce direct photoionization from the ground state only in the case of this metal.

  10. Evaluation of Finite-Rate GasSurface Interaction Models for a Carbon Based Ablator

    NASA Technical Reports Server (NTRS)

    Chen, Yih-Kanq; Goekcen, Tahir

    2015-01-01

    Two sets of finite-rate gas-surface interaction model between air and the carbon surface are studied. The first set is an engineering model with one-way chemical reactions, and the second set is a more detailed model with two-way chemical reactions. These two proposed models intend to cover the carbon surface ablation conditions including the low temperature rate-controlled oxidation, the mid-temperature diffusion-controlled oxidation, and the high temperature sublimation. The prediction of carbon surface recession is achieved by coupling a material thermal response code and a Navier-Stokes flow code. The material thermal response code used in this study is the Two-dimensional Implicit Thermal-response and Ablation Program, which predicts charring material thermal response and shape change on hypersonic space vehicles. The flow code solves the reacting full Navier-Stokes equations using Data Parallel Line Relaxation method. Recession analyses of stagnation tests conducted in NASA Ames Research Center arc-jet facilities with heat fluxes ranging from 45 to 1100 wcm2 are performed and compared with data for model validation. The ablating material used in these arc-jet tests is Phenolic Impregnated Carbon Ablator. Additionally, computational predictions of surface recession and shape change are in good agreement with measurement for arc-jet conditions of Small Probe Reentry Investigation for Thermal Protection System Engineering.

  11. Ablation Modeling of Ares-I Upper State Thermal Protection System Using Thermal Desktop

    NASA Technical Reports Server (NTRS)

    Sharp, John R.; Page, Arthur T.

    2007-01-01

    The thermal protection system (TPS) for the Ares-I Upper Stage will be based on Space Transportation System External Tank (ET) and Solid Rocket Booster (SRB) heritage materials. These TPS materials were qualified via hot gas testing that simulated ascent and re-entry aerothermodynamic convective heating environments. From this data, the recession rates due to ablation were characterized and used in thermal modeling for sizing the thickness required to maintain structural substrate temperatures. At Marshall Space Flight Center (MSFC), the in-house code ABL is currently used to predict TPS ablation and substrate temperatures as a FORTRAN application integrated within SINDA/G. This paper describes a comparison of the new ablation utility in Thermal Desktop and SINDA/FLUINT with the heritage ABL code and empirical test data which serves as the validation of the Thermal Desktop software for use on the design of the Ares-I Upper Stage project.

  12. Correlation between ultrasound reflection intensity and tumor ablation ratio of late-stage pancreatic carcinoma in HIFU therapy: dynamic observation on ultrasound reflection intensity.

    PubMed

    Ge, Hui-Yu; Miao, Li-Ying; Wang, Jin-Rui; Xiong, Liu-Lin; Yan, Fang; Zheng, Cui-Shan; Jia, Jian-Wen; Cui, Li-Gang; Chen, Wen

    2013-01-01

    The minimally invasive high-intensity focused ultrasound (HIFU) therapy is thermal ablation treatment for late-stage pancreatic carcinoma with widely recognized safety and effectiveness, but there are currently no instant assessment methods for its ablation effect. It is vital to find a real-time high-sensitive assessment method. This research aims to dynamically observe the variation rules of ultrasound reflection intensity, analyze the correlation between ultrasound reflection intensity and tumor ablation ratio, and find out the value of ultrasound reflection intensity in prognosis of HIFU ablation effect. HIFU intermittent therapies were retrospectively analyzed for 31 subjects with late-stage pancreatic carcinoma from March 2007 to December 2009 in the study. The variation rules of the ultrasound reflection intensity during HIFU therapy were summarized and the correlation between ultrasound reflection intensity and tumor ablation ratio was analyzed based on the tumor ablation ratio indicated by CT scanning. The conclusion is that variation of ultrasound reflection intensity can be used for initial assessment of tumor ablation in HIFU therapy and early prognosis of overall HIFU ablation, providing important clinical basis for improving safety and effectiveness of HIFU therapy. Ultrasound can work as a real-time imaging instrument for observation of HIFU ablation effect in treating late-stage pancreatic carcinoma.

  13. Understanding plume splitting of laser ablated plasma: A view from ion distribution dynamics

    SciTech Connect

    Wu, Jian; Li, Xingwen; Wei, Wenfu; Jia, Shenli; Qiu, Aici

    2013-11-15

    Plume splitting in low-pressure ambient air was understood in view of ion distribution dynamics from the laser ablated Al plasma (1064 nm 0.57 J/mm{sup 2}) by combining fast photography and spatially resolved spectroscopy. In the beginning, the spectral lines were mainly from the Al III ion. Then, the Bragg peak in stopping power of the ambient gas to Al III could be the dominant reason for the enhanced emission from the fast moving part, and the recombination of Al III to Al I-II ions near the target surface was response to the radiations from the slow moving/stationary part. As the ambient gas pressure increased, stopping distances of the Al III decreased, and radiation from the air ions became pronounced. The laser shadowgraph image at 1100 Pa indicated that the shock wave front located between the fast moving and slow moving parts. Electron densities of the fast moving plasma, which peaked at the plasma front, were on the order of 10{sup 16} cm{sup −3}, and the electron temperatures were 2–3 eV.

  14. Intramembranous bone regeneration and implant placement using mechanical femoral marrow ablation: rodent models.

    PubMed

    Moran, Meghan M; Sena, Kotaro; McNulty, Margaret A; Sumner, D R; Virdi, Amarjit S

    2016-01-01

    In this paper, we provide a detailed protocol for a model of long bone mechanical marrow ablation in the rodent, including surgical procedure, anesthesia, and pre- and post-operative care. In addition, frequently used experimental end points are briefly discussed. This model was developed to study intramembranous bone regeneration following surgical disruption of the marrow contents of long bones. In this model, the timing of the appearance of bone formation and remodeling is well-characterized and therefore the model is well-suited to evaluate the in vivo effects of various agents which influence these processes. When biomaterials such as tissue engineering scaffolds or metal implants are placed in the medullary cavity after marrow ablation, end points relevant to tissue engineering and implant fixation can also be analyzed. By sharing a detailed protocol, we hope to improve inter-laboratory reproducibility. PMID:27648259

  15. Fractal hydrodynamic model of high-fluence laser ablation plasma expansion

    SciTech Connect

    Agop, M.; Nica, P.; Gurlui, S.; Focsa, C.

    2010-10-08

    Optical/electrical characterization of transient plasmas generated by high-fluence (up to 1 kJ/cm{sup 2}) laser ablation of various targets revealed as a general feature the splitting of the plume in two structures. In order to account for this behavior, a new fractal hydrodynamic model has been developed in a non-differentiable space-time. The model successfully retrieves the kinetics of the two structures.

  16. Mathematical modeling of epicardial RF ablation of atrial tissue with overlying epicardial fat.

    PubMed

    Suárez, Ana González; Hornero, Fernando; Berjano, Enrique J

    2010-02-04

    The efficacy of treating atrial fibrillation by RF ablation on the epicardial surface is currently under question due to the presence of epicardial adipose tissue interposed between the ablation electrode and target site (atrial wall). The problem is probably caused by the electrical conductivity of the fat (0.02 S/m) being lower than that of the atrial tissue (0.4-0.6 S/m). Since our objective is to improve epicardial RF ablation techniques, we planned a study based on a two-dimensional mathematical model including an active electrode, a fragment of epicardial fat over a fragment of atrial tissue, and a section of atrium with circulating blood. Different procedures for applying RF power were studied, such as varying the frequency, using a cooled instead of a dry electrode, and different modes of controlling RF power (constant current, temperature and voltage) for different values of epicardial fat thickness. In general, the results showed that the epicardial fat layer seriously impedes the passage of RF current, thus reducing the effectiveness of atrial wall RF ablation.

  17. Mathematical Modeling of Epicardial RF Ablation of Atrial Tissue with Overlying Epicardial Fat

    PubMed Central

    Suárez, Ana González; Hornero, Fernando; Berjano, Enrique J.

    2010-01-01

    The efficacy of treating atrial fibrillation by RF ablation on the epicardial surface is currently under question due to the presence of epicardial adipose tissue interposed between the ablation electrode and target site (atrial wall). The problem is probably caused by the electrical conductivity of the fat (0.02 S/m) being lower than that of the atrial tissue (0.4-0.6 S/m). Since our objective is to improve epicardial RF ablation techniques, we planned a study based on a two-dimensional mathematical model including an active electrode, a fragment of epicardial fat over a fragment of atrial tissue, and a section of atrium with circulating blood. Different procedures for applying RF power were studied, such as varying the frequency, using a cooled instead of a dry electrode, and different modes of controlling RF power (constant current, temperature and voltage) for different values of epicardial fat thickness. In general, the results showed that the epicardial fat layer seriously impedes the passage of RF current, thus reducing the effectiveness of atrial wall RF ablation. PMID:20300229

  18. Enclosure fire dynamics model

    NASA Technical Reports Server (NTRS)

    Bellan, J.

    1979-01-01

    A practical situation of an enclosure fire is presented and why the need for a fire dynamic model is addressed. The difficulties in establishing a model are discussed, along with a brief review of enclosure fire models available. The approximation of the practical situation and the model developed are presented.

  19. Ablator Modeling: Why Not Much Has Changed Over the Past 45 plus Years

    NASA Technical Reports Server (NTRS)

    Laub, B.

    2011-01-01

    In the late 1950s, the earliest models describing the thermal response of ablative materials were based on the heat of ablation concept, which is an empirical approach that was reasonable for the types of materials of interest at that time. In the early-mid 60s the models were expanded to include pyrolysis since organic resin composites became the TPS materials of interest. However, surface recession was still predominantly modeled via empirical correlation. The development of the 1-D CMA finite difference code in the mid-late 60s introduced the thermochemical ablation approach for gas/surface interactions. Since that time investigators have developed finite volume and finite element codes, in 1-D, 2-D and 3-D, but the basic modeling has not evolved significantly. Models describing internal gas pressure due to pyrolysis, particle impact erosion, in-depth radiant transport, etc., have been added to address specific problems, but the fundamental modeling has not evolved. The reasons for this stagnation, as viewed by the author, will be described.

  20. A novel parameter for predicting arterial fusion and ablation in finite element models

    NASA Astrophysics Data System (ADS)

    Fankell, Douglas; Kramer, Eric; Taylor, Kenneth; Ferguson, Virginia; Rentschler, Mark E.

    2015-03-01

    Tissue fusion devices apply heat and pressure to ligate or ablate blood vessels during surgery. Although this process is widely used, a predictive finite element (FE) model incorporating both structural mechanics and heat transfer has not been developed, limiting improvements to empirical evidence. This work presents the development of a novel damage parameter, which incorporates stress, water content and temperature, and demonstrates its application in a FE model. A FE model, using the Holzapfel-Gasser-Ogden strain energy function to represent the structural mechanics and equations developed by Cezo to model water content and heat transfer, was created to simulate the fusion or ablation of a porcine splenic artery. Using state variables, the stresses, temperature and water content are recorded and combined to create a single parameter at each integration point. The parameter is then compared to a critical value (determined through experiments). If the critical value is reached, the element loses all strength. If the value is not reached, no change occurs. Little experimental data exists for validation, but the resulting stresses, temperatures and water content fall within ranges predicted by prior work. Due to the lack of published data, additional experimental studies are being conducted to rigorously validate and accurately determine the critical value. Ultimately, a novel method for demonstrating tissue damage and fusion in a FE model is presented, providing the first step towards in-depth FE models simulating fusion and ablation of arteries.

  1. Abrasion-ablation model for neutron production in heavy ion reactions

    NASA Technical Reports Server (NTRS)

    Cucinotta, Francis A.; Wilson, John W.; Townsend, Lawrence W.

    1995-01-01

    In heavy ion reactions, neutron production at forward angles is observed to occur with a Gaussian shape that is centered near the beam energy and extends to energies well above that of the beam. This paper presents an abrasion-ablation model for making quantitative predictions of the neutron spectrum. To describe neutrons produced from the abrasion step of the reaction where the projectile and target overlap, the authors use the Glauber model and include effects of final-state interactions. They then use the prefragment mass distribution from abrasion with a statistical evaporation model to estimate the neutron spectrum resulting from ablation. Measurements of neutron production from Ne and Nb beams are compared with calculations, and good agreement is found.

  2. Mouse Models in Orthopaedic Research: An Overview of Fracture, Marrow Ablation, and Distraction Osteogenesis

    PubMed Central

    Lybrand, Kyle; Bragdon, Beth; Gerstenfeld, Louis

    2015-01-01

    Three commonly used murine surgical models of bone healing (closed fracture with intramedullary fixation, distraction osteogenesis (DO), and marrow ablation by reaming) are presented. Detailed surgical protocols for each model are outlined. The nature of the regenerative processes and the types of research questions that may be addressed with these models are briefly outlined. The relative strengths and weaknesses of these models are compared to a number of other surgical models that are used to address similar research questions. Refer to our companion article for more detailed overview of the underlying biology of each model. PMID:25727199

  3. A preoperative mathematic model for computed tomographic guided microwave ablation treatment of hepatic dome tumors

    PubMed Central

    Yang, Bin; Xue, Jing-Bing; Mo, Zhi-Qiang; Zhong, Zhi-Hui; Zhang, Tao; Zhang, Fu-Jun; Fan, Wei-Jun

    2016-01-01

    Purpose This study sought to prospectively evaluate the feasibility and safety of a preoperative mathematic model for computed tomographic(CT) guided microwave(MW) ablation treatment of hepatic dome tumors. Methods This mathematic model was a regular cylinder quantifying appropriate puncture routes from the bottom up. A total of 103 patients with hepatic dome tumors were enrolled and randomly divided into 2 groups based on whether this model was used or not: Group A (using the model; n = 43) versus Group B (not using the model; n = 60). All tumors were treated by CT-guided MW ablation and follow-up contrast CT were reviewed. Results The average number of times for successful puncture, average ablation time, and incidence of right shoulder pain were less in Group A than Group B (1.4 vs. 2.5, P = 0.001; 8.8 vs. 11.1 minutes, P = 0.003; and 4.7% vs. 20%, P = 0.039). The technical success rate was higher in Group A than Group B (97.7% vs. 85.0%, P = 0.032). There were no significant differences between the two groups in primary and secondary technique efficacy rates (97.7% vs. 88.3%, P = 0.081; 90.0% vs. 72.7%, P = 0.314). No major complications occurred in both groups. Conclusion The mathematic model of regular cylinder is feasible and safe for CT-guided MW ablation in treating hepatic dome tumors. PMID:27028994

  4. Laser ablation of blepharopigmentation

    SciTech Connect

    Tanenbaum, M.; Karas, S.; McCord, C.D. Jr. )

    1988-01-01

    This article discusses laser ablation of blepharopigmentation in four stages: first, experimentally, where pigment vaporization is readily achieved with the argon blue-green laser; second, in the rabbit animal model, where eyelid blepharopigmentation markings are ablated with the laser; third, in human subjects, where the argon blue-green laser is effective in the ablation of implanted eyelid pigment; and fourth, in a case report, where, in a patient with improper pigment placement in the eyelid, the laser is used to safely and effectively ablate the undesired pigment markings. This article describes in detail the new technique of laser ablation of blepharopigmentation. Potential complications associated with the technique are discussed.

  5. Critical Fluences And Modeling Of CO{sub 2} Laser Ablation Of Polyoxymethylene From Vaporization To The Plasma Regime

    SciTech Connect

    Sinko, John E.; Phipps, Claude R.; Tsukiyama, Yosuke; Ogita, Naoya; Sasoh, Akihiro; Umehara, Noritsugu; Gregory, Don A.

    2010-05-06

    A CO{sub 2} laser was operated at pulse energies up to 10 J to ablate polyoxymethylene targets in air and vacuum conditions. Critical effects predicted by ablation models are discussed in relation to the experimental data, including specifically the threshold fluences for vaporization and critical plasma formation, and the fluence at which the optimal momentum coupling coefficient is found. Finally, we discuss a new approach for modeling polymers at long wavelengths, including a connection formula that links the vaporization and plasma regimes for laser ablation propulsion.

  6. An improved three-dimensional two-temperature model for multi-pulse femtosecond laser ablation of aluminum

    SciTech Connect

    Zhang, Jinping; Chen, Yuping Hu, Mengning; Chen, Xianfeng

    2015-02-14

    In this paper, an improved three-dimensional two-temperature model for multi-pulse femtosecond laser ablation of aluminum was proposed and proved in our experiment. Aiming to achieve hole-drilling with a high ratio of depth/entrance diameter in vacuum, this model can predict the depth and radius of the drilled holes precisely when employing different laser parameters. Additionally, for multi-pulse laser ablation, we found that the laser fluence and number of pulses are the dominant parameters and the multi-pulse ablation threshold is much lower than the single-pulse one, which will help to obtain high-quality holes.

  7. Modeling Climate Dynamically

    ERIC Educational Resources Information Center

    Walsh, Jim; McGehee, Richard

    2013-01-01

    A dynamical systems approach to energy balance models of climate is presented, focusing on low order, or conceptual, models. Included are global average and latitude-dependent, surface temperature models. The development and analysis of the differential equations and corresponding bifurcation diagrams provides a host of appropriate material for…

  8. Dynamics of vitellogenin and vitellogenesis-inhibiting hormone levels in adult and subadult whiteleg shrimp, Litopenaeus vannamei: relation to molting and eyestalk ablation.

    PubMed

    Kang, Bong Jung; Okutsu, Tomoyuki; Tsutsui, Naoaki; Shinji, Junpei; Bae, Sun-Hye; Wilder, Marcy N

    2014-01-01

    Levels of vitellogenin (VG) and vitellogenesis-inhibiting hormone (VIH) in the whiteleg shrimp, Litopenaeus vannamei, were measured by time-resolved fluoroimmunoassay in relation to the molting cycle and ovarian maturation induced by eyestalk ablation. During the molt cycle, VG mRNA expression levels and VG concentrations showed similar patterns of fluctuation. VG levels increased significantly at early intermolt (stage C0) in adults, but not in subadults. Unilateral and bilateral eyestalk ablation increased VG levels in adults, whereas only bilateral eyestalk ablation affected subadults. VIH levels showed contrasting patterns between adults and subadults. In adults, levels were high in late postmolt adults (stage B) and then low thereafter, whereas they increased from postmolt (stage A) to intermolt (stage C0) in subadults and remained high. Unilateral eyestalk ablation increased VIH levels 10 days following ablation in adults, after which levels decreased at 20 days. VIH levels decreased from 10 to 20 days after bilateral ablation. Both unilateral and bilateral ablation led to increased VIH levels in subadults. Eyestalk ablation induced ovarian maturation, but did not reduce VIH concentrations in the hemolymph. This phenomenon was perhaps due to other crustacean hyperglycemic hormone peptides having cross-reactivity with VIH antibodies. This is the first report to quantify concentrations of VG and VIH together in L. vannamei hemolymph, and to examine their relative dynamics.

  9. Femtosecond ultraviolet laser ablation of silver and comparison with nanosecond ablation

    SciTech Connect

    Toftmann, B.; Schou, J.; Doggett, B.; Budtz-Jorgensen, C.; Lunney, J. G.

    2013-02-28

    The ablation plume dynamics arising from ablation of silver with a 500 fs, 248 nm laser at {approx}2 J cm{sup -2} has been studied using angle-resolved Langmuir ion probe and thin film deposition techniques. For the same laser fluence, the time-of-flight ion signals from femtosecond and nanosecond laser ablation are similar; both show a singly peaked time-of-flight distribution. The angular distribution of ion emission and the deposition are well described by the adiabatic and isentropic model of plume expansion, though distributions for femtosecond ablation are significantly narrower. In this laser fluence regime, the energy efficiency of mass ablation is higher for femtosecond pulses than for nanosecond pulses, but the ion production efficiency is lower.

  10. Laser mass ablation efficiency measurements indicate bubble-driven dynamics dominates laser thrombolysis

    SciTech Connect

    Godwin, R.P.; Chapyak, E.J.; Prahl, S.A.; Shangguan, H.Q.

    1998-03-01

    Mass removal experiments have been performed at the Oregon Medical Laser Center with 10 to 100 mJ 1 {micro}s laser pulses at optical wavelengths. Above the energy threshold for bubble formation, the laser mass ablation efficiency ({micro}g/mJ) for removal of gel surrogate thrombus is nearly constant for a given experimental geometry and gel absorption coefficient. The efficiency in contact experiments, in which the optical fiber delivering the energy is in close proximity to the absorbing gel, is approximately three times that of non-contact experiments, in which the optical fiber is {approximately}1 mm from the gel. Mass removal occurs hundreds of microseconds after the laser deposition. Experimental data and numerical simulations are consistent with the hypothesis that jet formation during bubble collapse plays a dominant role in mass removal. This hypothesis suggests a model in which the mass removed scales linearly with the maximum bubble volume and explains the distinctive features, including the magnitude, of the mass removal.

  11. Creation of a Tumor-Mimic Model Using a Muscle Paste for Radiofrequency Ablation of the Lung

    SciTech Connect

    Kawai, T. Kaminou, T.; Sugiura, K.; Hashimoto, M.; Ohuchi, Y.; Adachi, A.; Fujioka, S.; Ito, H.; Nakamura, K.; Ogawa, T.

    2009-03-15

    The purpose of this study was to develop an easily created tumor-mimic model and evaluate its efficacy for radiofrequency ablation (RFA) of the lung. The bilateral lungs of eight living adult swine were used. A tumor-mimic model was made by percutaneous injection of 1.0 ml muscle paste through the bone biopsy needle into the lung. An RFA probe was then inserted into the tumor mimics immediately after tumor creation. Ablation time, tissue impedance, and temperature were recorded. The tumor mimics and their coagulated regions were evaluated microscopically and macroscopically. The muscle paste was easily injected into the lung parenchyma through the bone biopsy needle and well visualized under fluoroscopy. In 10 of 12 sites the tumor mimics were oval shaped, localized, and homogeneous on gross specimens. Ten tumor mimics were successfully ablated, and four locations were ablated in the normal lung parenchyma as controls. In the tumor and normal lung parenchyma, ablation times were 8.9 {+-} 3.5 and 4.4 {+-} 1.6 min, respectively; tissue impedances at the start of ablation were 100.6 {+-} 16.6 and 145.8 {+-} 26.8 {Omega}, respectively; and temperatures at the end of ablation were 66.0 {+-} 7.9 and 57.5 {+-} 7.6{sup o}C, respectively. The mean size of tumor mimics was 13.9 x 8.2 mm, and their coagulated area was 18.8 x 13.1 mm. In the lung parenchyma, the coagulated area was 15.3 x 12.0 mm. In conclusion, our tumor-mimic model using muscle paste can be easily and safely created and can be ablated using the ablation algorithm in the clinical setting.

  12. Modifying Wire Array Z-pinch Ablation Structure and Implosion Dynamics Using Coiled Arrays

    SciTech Connect

    Hall, Gareth N.; Bland, Simon N.; Lebedev, Sergey V.; Chittenden, Jeremy P.; Palmer, James B. A.; Suzuki-Vidal, Francisco A.; Swadling, George F.; Niasse, Nicolas; Knapp, P. F.; Blesener, I. C.; McBride, R. D.; Chalenski, D. A.; Bell, K. S.; Greenly, J. B.; Blanchard, T.; Wilhelm, H.; Hammer, D. A.; Kusse, B. R.; Bott, Simon C.

    2009-01-21

    Coiled arrays, a cylindrical array in which each wire is formed into a helix, suppress the modulation of ablation at the fundamental wavelength. Outside the vicinity of the wire cores, ablation flow from coiled arrays is modulated at the coil wavelength and has a 2-stream structure in the r,{theta} plane. Within the vicinity of the helical wires, ablation is concentrated at positions with the greatest azimuthal displacement and plasma is axially transported from these positions such that the streams become aligned with sections of the coil furthest from the array axis. The GORGON MHD code accurately reproduces this observed ablation structure, which can be understood in terms of JxB forces that result from the interaction of the global magnetic field with a helical current path as well as additional current paths suggested by the simulations. With this ability to control where ablation streamers occur, large wavelength coils were constructed such that the breaks that form in the wires had sufficient axial separation to prevent perturbations in the implosion sheath from merging. This produces a new mode of implosion in which the global instability can be controlled and perturbations correlated between all wires in an array. For large wavelength 8-wire coiled arrays, this produced a dramatic increase in x-ray power, equalling that of a 32-wire straight array. These experiments were carried out on the MAGPIE generator (1 MA, 240 ns) at Imperial College, and the COBRA generator (1 MA, 100 ns) at Cornell University.

  13. Theoretical modeling for radiofrequency ablation: state-of-the-art and challenges for the future

    PubMed Central

    Berjano, Enrique J

    2006-01-01

    Radiofrequency ablation is an interventional technique that in recent years has come to be employed in very different medical fields, such as the elimination of cardiac arrhythmias or the destruction of tumors in different locations. In order to investigate and develop new techniques, and also to improve those currently employed, theoretical models and computer simulations are a powerful tool since they provide vital information on the electrical and thermal behavior of ablation rapidly and at low cost. In the future they could even help to plan individual treatment for each patient. This review analyzes the state-of-the-art in theoretical modeling as applied to the study of radiofrequency ablation techniques. Firstly, it describes the most important issues involved in this methodology, including the experimental validation. Secondly, it points out the present limitations, especially those related to the lack of an accurate characterization of the biological tissues. After analyzing the current and future benefits of this technique it finally suggests future lines and trends in the research of this area. PMID:16620380

  14. Computational model of surface ablation from tokamak disruptions

    SciTech Connect

    Ehst, D.; Hassanein, A.

    1993-10-01

    Energy transfer to material surfaces is dominated by photon radiation through low temperature plasma vapors if tokamak disruptions are due to low kinetic energy particles ( < 100 eV). Simple models of radiation transport are derived and incorporated into a fast-running computer routine to model this process. The results of simulations are in fair agreement with plasma gun erosion tests on several metal targets.

  15. Chemical models for simulating single-walled nanotube production in arc vaporization and laser ablation processes

    NASA Technical Reports Server (NTRS)

    Scott, Carl D.

    2004-01-01

    Chemical kinetic models for the nucleation and growth of clusters and single-walled carbon nanotube (SWNT) growth are developed for numerical simulations of the production of SWNTs. Two models that involve evaporation and condensation of carbon and metal catalysts, a full model involving all carbon clusters up to C80, and a reduced model are discussed. The full model is based on a fullerene model, but nickel and carbon/nickel cluster reactions are added to form SWNTs from soot and fullerenes. The full model has a large number of species--so large that to incorporate them into a flow field computation for simulating laser ablation and arc processes requires that they be simplified. The model is reduced by defining large clusters that represent many various sized clusters. Comparisons are given between these models for cases that may be applicable to arc and laser ablation production. Solutions to the system of chemical rate equations of these models for a ramped temperature profile show that production of various species, including SWNTs, agree to within about 50% for a fast ramp, and within 10% for a slower temperature decay time.

  16. High speed direct imaging of thin metal film ablation by movie-mode dynamic transmission electron microscopy.

    PubMed

    Hihath, Sahar; Santala, Melissa K; Cen, Xi; Campbell, Geoffrey; van Benthem, Klaus

    2016-01-01

    Obliteration of matter by pulsed laser beams is not only prevalent in science fiction movies, but finds numerous technological applications ranging from additive manufacturing over machining of micro- and nanostructured features to health care. Pulse lengths ranging from femtoseconds to nanoseconds are utilized at varying laser beam energies and pulse lengths, and enable the removal of nanometric volumes of material. While the mechanisms for removal of material by laser irradiation, i.e., laser ablation, are well understood on the micrometer length scale, it was previously impossible to directly observe obliteration processes on smaller scales due to experimental limitations for the combination of nanometer spatial and nanosecond temporal resolution. Here, we report the direct observation of metal thin film ablation from a solid substrate through dynamic transmission electron microscopy. Quantitative analysis reveals liquid-phase dewetting of the thin-film, followed by hydrodynamic sputtering of nano- to submicron sized metal droplets. We discovered unexpected fracturing of the substrate due to evolving thermal stresses. This study confirms that hydrodynamic sputtering remains a valid mechanism for droplet expulsion on the nanoscale, while irradiation induced stress fields represent limit laser processing of nanostructured materials. Our results allow for improved safety during laser ablation in manufacturing and medical applications. PMID:26965073

  17. High speed direct imaging of thin metal film ablation by movie-mode dynamic transmission electron microscopy

    DOE PAGES

    Hihath, Sahar; Santala, Melissa K.; Cen, Xi; Campbell, Geoffrey; van Benthem, Klaus

    2016-03-11

    Obliteration of matter by pulsed laser beams is not only prevalent in science fiction movies, but finds numerous technological applications ranging from additive manufacturing over machining of micro- and nanostructured features to health care. Pulse lengths ranging from femtoseconds to nanoseconds are utilized at varying laser beam energies and pulse lengths, and enable the removal of nanometric volumes of material. While the mechanisms for removal of material by laser irradiation, i.e., laser ablation, are well understood on the micrometer length scale, it was previously impossible to directly observe obliteration processes on smaller scales due to experimental limitations for the combinationmore » of nanometer spatial and nanosecond temporal resolution. Here, we report the direct observation of metal thin film ablation from a solid substrate through dynamic transmission electron microscopy. Quantitative analysis reveals liquid-phase dewetting of the thin-film, followed by hydrodynamic sputtering of nano- to submicron sized metal droplets. We discovered unexpected fracturing of the substrate due to evolving thermal stresses. This study confirms that hydrodynamic sputtering remains a valid mechanism for droplet expulsion on the nanoscale, while irradiation induced stress fields represent limit laser processing of nanostructured materials. Ultimately, our results allow for improved safety during laser ablation in manufacturing and medical applications.« less

  18. High speed direct imaging of thin metal film ablation by movie-mode dynamic transmission electron microscopy

    PubMed Central

    Hihath, Sahar; Santala, Melissa K.; Cen, Xi; Campbell, Geoffrey; van Benthem, Klaus

    2016-01-01

    Obliteration of matter by pulsed laser beams is not only prevalent in science fiction movies, but finds numerous technological applications ranging from additive manufacturing over machining of micro- and nanostructured features to health care. Pulse lengths ranging from femtoseconds to nanoseconds are utilized at varying laser beam energies and pulse lengths, and enable the removal of nanometric volumes of material. While the mechanisms for removal of material by laser irradiation, i.e., laser ablation, are well understood on the micrometer length scale, it was previously impossible to directly observe obliteration processes on smaller scales due to experimental limitations for the combination of nanometer spatial and nanosecond temporal resolution. Here, we report the direct observation of metal thin film ablation from a solid substrate through dynamic transmission electron microscopy. Quantitative analysis reveals liquid-phase dewetting of the thin-film, followed by hydrodynamic sputtering of nano- to submicron sized metal droplets. We discovered unexpected fracturing of the substrate due to evolving thermal stresses. This study confirms that hydrodynamic sputtering remains a valid mechanism for droplet expulsion on the nanoscale, while irradiation induced stress fields represent limit laser processing of nanostructured materials. Our results allow for improved safety during laser ablation in manufacturing and medical applications. PMID:26965073

  19. High speed direct imaging of thin metal film ablation by movie-mode dynamic transmission electron microscopy

    NASA Astrophysics Data System (ADS)

    Hihath, Sahar; Santala, Melissa K.; Cen, Xi; Campbell, Geoffrey; van Benthem, Klaus

    2016-03-01

    Obliteration of matter by pulsed laser beams is not only prevalent in science fiction movies, but finds numerous technological applications ranging from additive manufacturing over machining of micro- and nanostructured features to health care. Pulse lengths ranging from femtoseconds to nanoseconds are utilized at varying laser beam energies and pulse lengths, and enable the removal of nanometric volumes of material. While the mechanisms for removal of material by laser irradiation, i.e., laser ablation, are well understood on the micrometer length scale, it was previously impossible to directly observe obliteration processes on smaller scales due to experimental limitations for the combination of nanometer spatial and nanosecond temporal resolution. Here, we report the direct observation of metal thin film ablation from a solid substrate through dynamic transmission electron microscopy. Quantitative analysis reveals liquid-phase dewetting of the thin-film, followed by hydrodynamic sputtering of nano- to submicron sized metal droplets. We discovered unexpected fracturing of the substrate due to evolving thermal stresses. This study confirms that hydrodynamic sputtering remains a valid mechanism for droplet expulsion on the nanoscale, while irradiation induced stress fields represent limit laser processing of nanostructured materials. Our results allow for improved safety during laser ablation in manufacturing and medical applications.

  20. High speed direct imaging of thin metal film ablation by movie-mode dynamic transmission electron microscopy.

    PubMed

    Hihath, Sahar; Santala, Melissa K; Cen, Xi; Campbell, Geoffrey; van Benthem, Klaus

    2016-03-11

    Obliteration of matter by pulsed laser beams is not only prevalent in science fiction movies, but finds numerous technological applications ranging from additive manufacturing over machining of micro- and nanostructured features to health care. Pulse lengths ranging from femtoseconds to nanoseconds are utilized at varying laser beam energies and pulse lengths, and enable the removal of nanometric volumes of material. While the mechanisms for removal of material by laser irradiation, i.e., laser ablation, are well understood on the micrometer length scale, it was previously impossible to directly observe obliteration processes on smaller scales due to experimental limitations for the combination of nanometer spatial and nanosecond temporal resolution. Here, we report the direct observation of metal thin film ablation from a solid substrate through dynamic transmission electron microscopy. Quantitative analysis reveals liquid-phase dewetting of the thin-film, followed by hydrodynamic sputtering of nano- to submicron sized metal droplets. We discovered unexpected fracturing of the substrate due to evolving thermal stresses. This study confirms that hydrodynamic sputtering remains a valid mechanism for droplet expulsion on the nanoscale, while irradiation induced stress fields represent limit laser processing of nanostructured materials. Our results allow for improved safety during laser ablation in manufacturing and medical applications.

  1. Cell death, perfusion and electrical parameters are critical in models of hepatic radiofrequency ablation

    PubMed Central

    Hall, Sheldon K.; Ooi, Ean H.; Payne, Stephen J.

    2015-01-01

    Abstract Purpose: A sensitivity analysis has been performed on a mathematical model of radiofrequency ablation (RFA) in the liver. The purpose of this is to identify the most important parameters in the model, defined as those that produce the largest changes in the prediction. This is important in understanding the role of uncertainty and when comparing the model predictions to experimental data. Materials and methods: The Morris method was chosen to perform the sensitivity analysis because it is ideal for models with many parameters or that take a significant length of time to obtain solutions. A comprehensive literature review was performed to obtain ranges over which the model parameters are expected to vary, crucial input information. Results: The most important parameters in predicting the ablation zone size in our model of RFA are those representing the blood perfusion, electrical conductivity and the cell death model. The size of the 50 °C isotherm is sensitive to the electrical properties of tissue while the heat source is active, and to the thermal parameters during cooling. Conclusions: The parameter ranges chosen for the sensitivity analysis are believed to represent all that is currently known about their values in combination. The Morris method is able to compute global parameter sensitivities taking into account the interaction of all parameters, something that has not been done before. Research is needed to better understand the uncertainties in the cell death, electrical conductivity and perfusion models, but the other parameters are only of second order, providing a significant simplification. PMID:26000972

  2. History, ethics, advantages and limitations of experimental models for hepatic ablation

    PubMed Central

    Ong, Seok Ling; Gravante, Gianpiero; Metcalfe, Matthew S; Dennison, Ashley R

    2013-01-01

    Numerous techniques developed in medicine require careful evaluation to determine their indications, limitations and potential side effects prior to their clinical use. At present this generally involves the use of animal models which is undesirable from an ethical standpoint, requires complex and time-consuming authorization, and is very expensive. This process is exemplified in the development of hepatic ablation techniques, starting experiments on explanted livers and progressing to safety and efficacy studies in living animals prior to clinical studies. The two main approaches used are ex vivo isolated non-perfused liver models and in vivo animal models. Ex vivo non perfused models are less expensive, easier to obtain but not suitable to study the heat sink effect or experiments requiring several hours. In vivo animal models closely resemble clinical subjects but often are expensive and have small sample sizes due to ethical guidelines. Isolated perfused ex vivo liver models have been used to study drug toxicity, liver failure, organ transplantation and hepatic ablation and combine advantages of both previous models. PMID:23345935

  3. Analysis of Charge Changing Cross Sections with the Glauber-Abrasion-Ablation Model

    NASA Astrophysics Data System (ADS)

    Akaishi, Tomohide; Hagino, Kouichi

    We calculate the charge changing cross sections (CCCS) for 28Si + 12C reaction using the Glauber-abrasion-ablation model, which considers a fragment-production in two stages, that is, a fragmentation and particle evaporations. We show that this model underestimates CCCS in a wide energy region if only the first stage is taken into account. This is the case both in the optical limit approximation (OLA) and in the beyond OLA calculation. This indicates that the second stage for the particle evaporation has to be taken into account in order to quantitatively estimate CCCS.

  4. Nonthermal Ablation by Using Intravascular Oxygen Radical Generation with WST11: Dynamic Tissue Effects and Implications for Focal Therapy.

    PubMed

    Kimm, Simon Y; Tarin, Tatum V; Monette, Sébastien; Srimathveeravalli, Govindarajan; Gerber, Daniel; Durack, Jeremy C; Solomon, Stephen B; Scardino, Peter T; Scherz, Avigdor; Coleman, Jonathan

    2016-10-01

    Purpose To examine the hypothesis that vascular-targeted photodynamic therapy (VTP) with WST11 and clinically relevant parameters can be used to ablate target tissues in a non-tumor-bearing large-animal model while selectively sparing blood vessels and collagen. Materials and Methods By using an institutional animal care and use committee-approved protocol, 68 ablations were performed in the kidneys (cortex and medulla) and livers of 27 adult pigs. Posttreatment evaluation was conducted with contrast material-enhanced computed tomography in the live animals at 24 hours. Immunohistochemistry was evaluated and histologic examination with hematoxylin-eosin staining was performed at 4 hours, 24 hours, and 7 days. Intravenous infusion of WST11 (4 mg per kilogram of body weight) was followed by using near-infrared illumination (753 nm for 20 minutes) through optical fibers prepositioned in target tissues by using a fixed template. Treated areas were scanned, measured, and statistically analyzed by using the Student t test and two-way analysis of variance. Results Focal WST11 VTP treatment in the liver and kidney by using a single optical fiber resulted in well-demarcated cylindrical zones of nonthermal necrosis concentrically oriented around the light-emitting diffuser, with no intervening viable parenchymal cells. The radius of ablated tissue increased from approximately 5 mm at 150 mW to approximately 7 mm at 415 mW (P < .01). Illumination through fiber triads at 1-cm separation resulted in confluent homogeneous necrosis. Patterns of acute injury within 24 hours were consistent with microcirculatory flow arrest and collagen preservation (demonstrated with trichrome staining). In the peripheral ablation zone, blood vessels at least 40 μm in diameter were selectively preserved and remained functional at 7 days. Ablated tissues exhibited progressive fibrosis and chronic inflammatory cell infiltrates. No histologic changes consistent with thermal injury were observed in

  5. Nonthermal Ablation by Using Intravascular Oxygen Radical Generation with WST11: Dynamic Tissue Effects and Implications for Focal Therapy.

    PubMed

    Kimm, Simon Y; Tarin, Tatum V; Monette, Sébastien; Srimathveeravalli, Govindarajan; Gerber, Daniel; Durack, Jeremy C; Solomon, Stephen B; Scardino, Peter T; Scherz, Avigdor; Coleman, Jonathan

    2016-10-01

    Purpose To examine the hypothesis that vascular-targeted photodynamic therapy (VTP) with WST11 and clinically relevant parameters can be used to ablate target tissues in a non-tumor-bearing large-animal model while selectively sparing blood vessels and collagen. Materials and Methods By using an institutional animal care and use committee-approved protocol, 68 ablations were performed in the kidneys (cortex and medulla) and livers of 27 adult pigs. Posttreatment evaluation was conducted with contrast material-enhanced computed tomography in the live animals at 24 hours. Immunohistochemistry was evaluated and histologic examination with hematoxylin-eosin staining was performed at 4 hours, 24 hours, and 7 days. Intravenous infusion of WST11 (4 mg per kilogram of body weight) was followed by using near-infrared illumination (753 nm for 20 minutes) through optical fibers prepositioned in target tissues by using a fixed template. Treated areas were scanned, measured, and statistically analyzed by using the Student t test and two-way analysis of variance. Results Focal WST11 VTP treatment in the liver and kidney by using a single optical fiber resulted in well-demarcated cylindrical zones of nonthermal necrosis concentrically oriented around the light-emitting diffuser, with no intervening viable parenchymal cells. The radius of ablated tissue increased from approximately 5 mm at 150 mW to approximately 7 mm at 415 mW (P < .01). Illumination through fiber triads at 1-cm separation resulted in confluent homogeneous necrosis. Patterns of acute injury within 24 hours were consistent with microcirculatory flow arrest and collagen preservation (demonstrated with trichrome staining). In the peripheral ablation zone, blood vessels at least 40 μm in diameter were selectively preserved and remained functional at 7 days. Ablated tissues exhibited progressive fibrosis and chronic inflammatory cell infiltrates. No histologic changes consistent with thermal injury were observed in

  6. Nonthermal ablation of deep brain targets: A simulation study on a large animal model

    PubMed Central

    Top, Can Barış; White, P. Jason; McDannold, Nathan J.

    2016-01-01

    Purpose: Thermal ablation with transcranial MRI-guided focused ultrasound (FUS) is currently limited to central brain targets because of heating and other beam effects caused by the presence of the skull. Recently, it was shown that it is possible to ablate tissues without depositing thermal energy by driving intravenously administered microbubbles to inertial cavitation using low-duty-cycle burst sonications. A recent study demonstrated that this ablation method could ablate tissue volumes near the skull base in nonhuman primates without thermally damaging the nearby bone. However, blood–brain disruption was observed in the prefocal region, and in some cases, this region contained small areas of tissue damage. The objective of this study was to analyze the experimental model with simulations and to interpret the cause of these effects. Methods: The authors simulated prior experiments where nonthermal ablation was performed in the brain in anesthetized rhesus macaques using a 220 kHz clinical prototype transcranial MRI-guided FUS system. Low-duty-cycle sonications were applied at deep brain targets with the ultrasound contrast agent Definity. For simulations, a 3D pseudospectral finite difference time domain tool was used. The effects of shear mode conversion, focal steering, skull aberrations, nonlinear propagation, and the presence of skull base on the pressure field were investigated using acoustic and elastic wave propagation models. Results: The simulation results were in agreement with the experimental findings in the prefocal region. In the postfocal region, however, side lobes were predicted by the simulations, but no effects were evident in the experiments. The main beam was not affected by the different simulated scenarios except for a shift of about 1 mm in peak position due to skull aberrations. However, the authors observed differences in the volume, amplitude, and distribution of the side lobes. In the experiments, a single element passive

  7. A genetic mouse model for progressive ablation and regeneration of insulin producing beta-cells

    PubMed Central

    Shamsi, Farnaz; Parlato, Rosanna; Collombat, Patrick; Mansouri, Ahmed

    2014-01-01

    The putative induction of adult β-cell regeneration represents a promising approach for the treatment of type 1 diabetes. Toward this ultimate goal, it is essential to develop an inducible model mimicking the long-lasting disease progression. In the current study, we have established a novel β-cell ablation mouse model, in which the β-cell mass progressively declines, as seen in type 1 diabetes. The model is based on the β-cell specific genetic ablation of the transcription initiation factor 1A, TIF-IA, essential for RNA Polymerase I activity (TIF-IAΔ/Δ). Using this approach, we induced a slow apoptotic response that eventually leads to a protracted β-cell death. In this model, we observed β-cell regeneration that resulted in a complete recovery of the β-cell mass and normoglycemia. In addition, we showed that adaptive proliferation of remaining β-cells is the prominent mechanism acting to compensate for the massive β-cell loss in young but also aged mice. Interestingly, at any age, we also detected β-like cells expressing the glucagon hormone, suggesting a transition between α- and β-cell identities or vice versa. Taken together, the TIF-IAΔ/Δ mouse model can be used to investigate the potential therapeutic approaches for type 1 diabetes targeting β-cell regeneration. PMID:25558832

  8. Validation of PICA Ablation and Thermal-Response Model at Low Heat Flux

    NASA Technical Reports Server (NTRS)

    Milos, Frank S.; Chen, Yih-Kanq

    2009-01-01

    Phenolic Impregnated Carbon Ablator (PICA) was the forebody heatshield material on the Stardust sample-return capsule and is also a primary candidate material for the Mars Science Lander (MSL), the Orion Crew Module, and the SpaceX Dragon vehicle. As part of the heatshield qualification for Orion, physical and thermal properties of virgin and charred PICA were measured, and an ablation and thermal response model was developed. We validated the model by comparing it with recession and temperature data from stagnation arcjet tests conducted over a wide range of stagnation heat flux of 107 to 1102 W/sq cm. The effect of orthotropic thermal conductivity was evident in the thermal response of the arcjet models. In general, model predictions compared well with the data; however, the uncertainty of the recession prediction was greatest for heat fluxes below 200 W/sq cm. More recent MSL testing focused on the low heat flux regime of 45 to 250 W/sq cm. The new results confirm the recession uncertainty, especially for pressures below 6 kPa. In this work we focus on improving the model predictions for MSL and Orion tests below 250 W/sq cm.

  9. MRI Reconstructions of Human Phrenic Nerve Anatomy and Computational Modeling of Cryoballoon Ablative Therapy.

    PubMed

    Goff, Ryan P; Spencer, Julianne H; Iaizzo, Paul A

    2016-04-01

    The primary goal of this computational modeling study was to better quantify the relative distance of the phrenic nerves to areas where cryoballoon ablations may be applied within the left atria. Phrenic nerve injury can be a significant complication of applied ablative therapies for treatment of drug refractory atrial fibrillation. To date, published reports suggest that such injuries may occur more frequently in cryoballoon ablations than in radiofrequency therapies. Ten human heart-lung blocs were prepared in an end-diastolic state, scanned with MRI, and analyzed using Mimics software as a means to make anatomical measurements. Next, generated computer models of ArticFront cryoballoons (23, 28 mm) were mated with reconstructed pulmonary vein ostias to determine relative distances between the phrenic nerves and projected balloon placements, simulating pulmonary vein isolation. The effects of deep seating balloons were also investigated. Interestingly, the relative anatomical differences in placement of 23 and 28 mm cryoballoons were quite small, e.g., the determined difference between mid spline distance to the phrenic nerves between the two cryoballoon sizes was only 1.7 ± 1.2 mm. Furthermore, the right phrenic nerves were commonly closer to the pulmonary veins than the left, and surprisingly tips of balloons were further from the nerves, yet balloon size choice did not significantly alter calculated distance to the nerves. Such computational modeling is considered as a useful tool for both clinicians and device designers to better understand these associated anatomies that, in turn, may lead to optimization of therapeutic treatments. PMID:26168718

  10. A Short Review of Ablative-Material Response Models and Simulation Tools

    NASA Technical Reports Server (NTRS)

    Lachaud, Jean; Magin, Thierry E.; Cozmuta, Ioana; Mansour, Nagi N.

    2011-01-01

    A review of the governing equations and boundary conditions used to model the response of ablative materials submitted to a high-enthalpy flow is proposed. The heritage of model-development efforts undertaken in the 1960s is extremely clear: the bases of the models used in the community are mathematically equivalent. Most of the material-response codes implement a single model in which the equation parameters may be modified to model different materials or conditions. The level of fidelity of the models implemented in design tools only slightly varies. Research and development codes are generally more advanced but often not as robust. The capabilities of each of these codes are summarized in a color-coded table along with research and development efforts currently in progress.

  11. Dynamical model for thyroid

    NASA Astrophysics Data System (ADS)

    Rokni Lamooki, Gholam Reza; Shirazi, Amir H.; Mani, Ali R.

    2015-05-01

    Thyroid's main chemical reactions are employed to develop a mathematical model. The presented model is based on differential equations where their dynamics reflects many aspects of thyroid's behavior. Our main focus here is the well known, but not well understood, phenomenon so called as Wolff-Chaikoff effect. It is shown that the inhibitory effect of intake iodide on the rate of one single enzyme causes a similar effect as Wolff-Chaikoff. Besides this issue, the presented model is capable of revealing other complex phenomena of thyroid hormones homeostasis.

  12. Modeling of the Ablation of Fibrous Materials in the Knudsen Regime

    NASA Technical Reports Server (NTRS)

    Lachaud, J.; Mansour, N. N.

    2008-01-01

    During atmospheric entry of planetary probes, the thermal protection system (TPS) of the probe is exposed to high temperatures under low pressures. In these conditions, carbonous TPS materials undergo gasification in the Knudsen regime leading to mass loss and wall recession called ablation. This work aims to improve the understanding of materiaVenvironment interactions through a study of the coupling between carbon dioxide transport in the Knudsen regime, heterogeneous oxidation of carbon, and sutface recession. A 3D Monte-Carlo simulation tool is used for this study. The fibrous architecture of the materiils, consisting of high porosity random array of carbon fibers, is numerically reproduced on a 3D Cartesian grid. Mass transport in the Knudsen regime from the boundary layer to the surface, and inside this porous material is simulated by random walk. A reaction probability is used to simulate the heterogeneous oxidation reaction. The surface recession is followed by front tracking using a simplified marching cube approach. The output data of the simulations are ablation velocity and dynamic evolution of the material porosity. A parametric study is carried out to analyze the material behavior as a function of Knudsen number for the porous media (length of the mean free path compared to the mean pore diameter) and the intrinsic reactivity of the carbon fibers. The results enable extrapolation of laboratory experimental data to actual entry conditions.

  13. Nonequilibrium Ablation of Phenolic Impregnated Carbon Ablator

    NASA Technical Reports Server (NTRS)

    Milos, Frank S.; Chen, Yih K.; Gokcen, Tahir

    2012-01-01

    In previous work, an equilibrium ablation and thermal response model for Phenolic Impregnated Carbon Ablator was developed. In general, over a wide range of test conditions, model predictions compared well with arcjet data for surface recession, surface temperature, in-depth temperature at multiple thermocouples, and char depth. In this work, additional arcjet tests were conducted at stagnation conditions down to 40 W/sq cm and 1.6 kPa. The new data suggest that nonequilibrium effects become important for ablation predictions at heat flux or pressure below about 80 W/sq cm or 10 kPa, respectively. Modifications to the ablation model to account for nonequilibrium effects are investigated. Predictions of the equilibrium and nonequilibrium models are compared with the arcjet data.

  14. Modelling distributed ablation on Juncal Norte Glacier, dry Andes of central Chile

    NASA Astrophysics Data System (ADS)

    Carenzo, Marco; Pellicciotti, Francesca; Helbing, Jakob; Dadic, Ruzica; Burlando, Paolo

    2010-05-01

    In the Aconcagua River Basin, in the dry Andes of central Chile, water resources in summer originate mostly from snow and ice glacier melt. Summer seasons are dry and stable, with precipitation close to zero, low relative humidity and very intense solar radiation. The region's economic activities are dependent on these water resources, but their assessment is still incomplete and an effort is needed to evaluate present and future changes in water from glacier and seasonal snow covers in this area. The main aim of this paper is to simulate glacier melt and runoff from Juncal Norte Glacier, in the upper Aconcagua Basin, using models of various complexity and data requirement. We simulate distributed glacier ablation for two seasons using an energy-balance model (EB) and an enhanced temperature-index model (ETI). Meteorological variables measured at Automatic Weather Stations (AWSs) located on and off-glacier are extrapolated from point observations to the glacier-wide scale. Shortwave radiation is modelled with a parametric model taking into account shading, reflection from slopes and atmospheric transmittance. In the energy-balance model, the longwave radiation flux is computed from Stefan-Boltzmann relationships and turbulent fluxes are calculated using the bulk aerodynamic method. The EB model includes subsurface heat conduction and gravitational redistribution of snow. Glacier runoff is modelled using a linear reservoir approach accounting for the temporal evolution of the system. Hourly simulations of glacier melt are validated against ablation observations (ultrasonic depth gauge and ablation stakes) and runoff measured at the glacier snout is compared to a runoff record obtained from a combination of radar water level measurements and tracer experiments. Results show that extrapolation of meteorological input data, and of temperature in particular, is the largest source of model uncertainty, together with snow water equivalent initial conditions. We explore

  15. Altered lymph node composition in diphtheria toxin receptor-based mouse models to ablate dendritic cells

    PubMed Central

    van Blijswijk, Janneke; Schraml, Barbara U.; Rogers, Neil C.; Whitney, Paul G.; Zelenay, Santiago; Acton, Sophie E.; Sousa, Caetano Reis e

    2014-01-01

    Dendritic cells (DCs) are key regulators of innate and adaptive immunity. Our understanding of immune function has benefited greatly from mouse models allowing for selective ablation of DCs. Many such models rely on transgenic diphtheria toxin receptor (DTR) expression driven by DC-restricted promoters. This renders DCs sensitive to DT but is otherwise thought to have no effect on immune physiology. Here, we report that, unexpectedly, mice in which DTR is expressed on conventional DCs display marked lymph node (LN) hypocellularity and reduced frequency of DCs in the same organs but not in spleen or non-lymphoid tissues. Intriguingly, in mixed bone marrow (BM) chimeras the phenotype conferred by DTR-expressing DCs is dominant over control BM-derived cells, leading to small LNs and an overall paucity of DCs independently of the genetic ability to express DTR. The finding of alterations in LN composition and size independently of diphtheria toxin challenge suggests that caution must be exercised when interpreting results of experiments obtained with mouse models to inducibly deplete DCs. It further indicates that DTR, a member of the epidermal growth factor family, is biologically active in mice. Its use in cell ablation experiments needs to be considered in light of this activity. PMID:25411201

  16. Computer Modeling for Microwave Ablation in Breast Cancer Using a Coaxial Slot Antenna

    NASA Astrophysics Data System (ADS)

    Cepeda Rubio, Mario Francisco Jesus; Guerrero López, Geshel David; Valdés Perezgasga, Francisco; Flores García, Francisco; Vera Hernández, Arturo; Leija Salas, Lorenzo

    2015-11-01

    The use of breast cancer mammography screening has allowed detection of a greater number of small carcinomas, and this has facilitated treatment by minimally invasive techniques. Microwave energy is a promising alternative treatment because it can preferentially heat and damage high-water-content breast carcinomas. In order to evaluate the feasibility of using this technique to treat breast cancer, a coaxial slot antenna computer simulation based on an axisymmetric finite element method (FEM) model was used to compare heating differences between cancer and normal breast tissue. Three FEM computer models were developed: in one of them, the coaxial slot antenna was immersed only in homogeneous breast tissue; for the second one, the antenna was immersed only in cancer tissue; for the third one, the antenna was inserted into malignant tissue surrounded by breast tissue. According to the results, the computer modeling demonstrated that the difference in dielectric properties and thermal parameters between malignant and normal adipose-dominated tissue was able to cause preferential heating of tumors during microwave ablation. Furthermore, the ablation zone radius was 42 % larger in the tumor than in low-water-content adipose tissue. Even though this technique requires further research, it is a promising minimally invasive modality for the local treatment of breast cancer.

  17. Ablation threshold and ablation mechanism transition of polyoxymethylene irradiated by CO2 laser.

    PubMed

    Li, Gan; Cheng, Mousen; Li, Xiaokang

    2016-09-01

    Polyoxymethylene (POM) decomposes gradually as it is heated up by the irradiation of CO2 laser; the long-chain molecules of POM are broken into short chains, which leads to the lowering of the melting point and the critical temperature of the ablation products. When the product temperature is above the melting point, ablation comes up in the way of vaporization; when the product temperature is higher than the critical temperature, all liquid products are transformed into gas instantly and the ablation mechanism is changed. The laser fluence at which significant ablation is observed is defined as the ablation threshold, and the fluence corresponding to the ablation mechanism changing is denoted as the flyover threshold. In this paper, random pyrolysis is adopted to describe the pyrolytic decomposition of POM, and consequently, the components of the pyrolysis products under different pyrolysis rates are acquired. The Group Contribution method is used to count the thermodynamic properties of the pyrolysis products, and the melting point and the critical temperature of the product mixture are obtained by the Mixing Law. The Knudsen layer relationship is employed to evaluate the ablation mass removal when the product temperature is below the critical temperature. The gas dynamics conservation laws associated with the Jouguet condition are used to calculate the mass removal when the product temperature is higher than the critical temperature. Based on the model, a set of simulations for various laser intensities and lengths are carried out to generalize the relationships between the thresholds and the laser parameters. Besides the ablated mass areal density, which fits the experimental data quite well, the ablation temperature, pyrolysis rate, and product components are also discussed for a better understanding of the ablation mechanism of POM.

  18. Ablation threshold and ablation mechanism transition of polyoxymethylene irradiated by CO2 laser.

    PubMed

    Li, Gan; Cheng, Mousen; Li, Xiaokang

    2016-09-01

    Polyoxymethylene (POM) decomposes gradually as it is heated up by the irradiation of CO2 laser; the long-chain molecules of POM are broken into short chains, which leads to the lowering of the melting point and the critical temperature of the ablation products. When the product temperature is above the melting point, ablation comes up in the way of vaporization; when the product temperature is higher than the critical temperature, all liquid products are transformed into gas instantly and the ablation mechanism is changed. The laser fluence at which significant ablation is observed is defined as the ablation threshold, and the fluence corresponding to the ablation mechanism changing is denoted as the flyover threshold. In this paper, random pyrolysis is adopted to describe the pyrolytic decomposition of POM, and consequently, the components of the pyrolysis products under different pyrolysis rates are acquired. The Group Contribution method is used to count the thermodynamic properties of the pyrolysis products, and the melting point and the critical temperature of the product mixture are obtained by the Mixing Law. The Knudsen layer relationship is employed to evaluate the ablation mass removal when the product temperature is below the critical temperature. The gas dynamics conservation laws associated with the Jouguet condition are used to calculate the mass removal when the product temperature is higher than the critical temperature. Based on the model, a set of simulations for various laser intensities and lengths are carried out to generalize the relationships between the thresholds and the laser parameters. Besides the ablated mass areal density, which fits the experimental data quite well, the ablation temperature, pyrolysis rate, and product components are also discussed for a better understanding of the ablation mechanism of POM. PMID:27607281

  19. Modeling earthquake dynamics

    NASA Astrophysics Data System (ADS)

    Charpentier, Arthur; Durand, Marilou

    2015-07-01

    In this paper, we investigate questions arising in Parsons and Geist (Bull Seismol Soc Am 102:1-11, 2012). Pseudo causal models connecting magnitudes and waiting times are considered, through generalized regression. We do use conditional model (magnitude given previous waiting time, and conversely) as an extension to joint distribution model described in Nikoloulopoulos and Karlis (Environmetrics 19: 251-269, 2008). On the one hand, we fit a Pareto distribution for earthquake magnitudes, where the tail index is a function of waiting time following previous earthquake; on the other hand, waiting times are modeled using a Gamma or a Weibull distribution, where parameters are functions of the magnitude of the previous earthquake. We use those two models, alternatively, to generate the dynamics of earthquake occurrence, and to estimate the probability of occurrence of several earthquakes within a year or a decade.

  20. Mesoscale ocean dynamics modeling

    SciTech Connect

    mHolm, D.; Alber, M.; Bayly, B.; Camassa, R.; Choi, W.; Cockburn, B.; Jones, D.; Lifschitz, A.; Margolin, L.; Marsden, L.; Nadiga, B.; Poje, A.; Smolarkiewicz, P.; Levermore, D.

    1996-05-01

    This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The ocean is a very complex nonlinear system that exhibits turbulence on essentially all scales, multiple equilibria, and significant intrinsic variability. Modeling the ocean`s dynamics at mesoscales is of fundamental importance for long-time-scale climate predictions. A major goal of this project has been to coordinate, strengthen, and focus the efforts of applied mathematicians, computer scientists, computational physicists and engineers (at LANL and a consortium of Universities) in a joint effort addressing the issues in mesoscale ocean dynamics. The project combines expertise in the core competencies of high performance computing and theory of complex systems in a new way that has great potential for improving ocean models now running on the Connection Machines CM-200 and CM-5 and on the Cray T3D.

  1. Model for macroevolutionary dynamics.

    PubMed

    Maruvka, Yosef E; Shnerb, Nadav M; Kessler, David A; Ricklefs, Robert E

    2013-07-01

    The highly skewed distribution of species among genera, although challenging to macroevolutionists, provides an opportunity to understand the dynamics of diversification, including species formation, extinction, and morphological evolution. Early models were based on either the work by Yule [Yule GU (1925) Philos Trans R Soc Lond B Biol Sci 213:21-87], which neglects extinction, or a simple birth-death (speciation-extinction) process. Here, we extend the more recent development of a generic, neutral speciation-extinction (of species)-origination (of genera; SEO) model for macroevolutionary dynamics of taxon diversification. Simulations show that deviations from the homogeneity assumptions in the model can be detected in species-per-genus distributions. The SEO model fits observed species-per-genus distributions well for class-to-kingdom-sized taxonomic groups. The model's predictions for the appearance times (the time of the first existing species) of the taxonomic groups also approximately match estimates based on molecular inference and fossil records. Unlike estimates based on analyses of phylogenetic reconstruction, fitted extinction rates for large clades are close to speciation rates, consistent with high rates of species turnover and the relatively slow change in diversity observed in the fossil record. Finally, the SEO model generally supports the consistency of generic boundaries based on morphological differences between species and provides a comparator for rates of lineage splitting and morphological evolution. PMID:23781101

  2. Model for macroevolutionary dynamics.

    PubMed

    Maruvka, Yosef E; Shnerb, Nadav M; Kessler, David A; Ricklefs, Robert E

    2013-07-01

    The highly skewed distribution of species among genera, although challenging to macroevolutionists, provides an opportunity to understand the dynamics of diversification, including species formation, extinction, and morphological evolution. Early models were based on either the work by Yule [Yule GU (1925) Philos Trans R Soc Lond B Biol Sci 213:21-87], which neglects extinction, or a simple birth-death (speciation-extinction) process. Here, we extend the more recent development of a generic, neutral speciation-extinction (of species)-origination (of genera; SEO) model for macroevolutionary dynamics of taxon diversification. Simulations show that deviations from the homogeneity assumptions in the model can be detected in species-per-genus distributions. The SEO model fits observed species-per-genus distributions well for class-to-kingdom-sized taxonomic groups. The model's predictions for the appearance times (the time of the first existing species) of the taxonomic groups also approximately match estimates based on molecular inference and fossil records. Unlike estimates based on analyses of phylogenetic reconstruction, fitted extinction rates for large clades are close to speciation rates, consistent with high rates of species turnover and the relatively slow change in diversity observed in the fossil record. Finally, the SEO model generally supports the consistency of generic boundaries based on morphological differences between species and provides a comparator for rates of lineage splitting and morphological evolution.

  3. Visual TSUNAMI: A Versatile, User-Friendly, Multidimensional Ablation and Gas-Dynamics Design Code

    SciTech Connect

    Debonnel, C.S.; Wang, T.X.; Suzuki, M.; Garcia, E.; Peterson, P.F.

    2005-05-15

    Gas dynamics phenomena in thick-liquid protected inertial fusion target chambers have been explored since the early 1990's with the help of a series of simulation codes known as TSUNAMI. The code has been recently redesigned entirely to make use of modern programming techniques, languages and software; improve its user-friendliness; and refine its ability to model thick-liquid protected chambers, while expanding its capability to a larger variety of systems. The new code is named 'Visual Tsunami' to emphasize the programming language of its core, Fortran 95, as well as its graphics-based input file builder and output processors. It is aimed at providing a user-friendly design tool for complex systems for which transient gas dynamics phenomena play a key role.

  4. Modeling Initial Stage of Ablation Material Pyrolysis: Graphitic Precursor Formation and Interfacial Effects

    NASA Technical Reports Server (NTRS)

    Desai, Tapan G.; Lawson, John W.; Keblinski, Pawel

    2010-01-01

    Reactive molecular dynamics simulations are used to study initial stage of pyrolysis of ablation materials and their composites with carbon nanotubes and carbon fibers. The products formed during pyrolysis are characterized and water is found as the primary product in all cases. The water formation mechanisms are analyzed and the value of the activation energy for water formation is estimated. A detailed study on graphitic precursor formation reveals the presence of two temperature zones. In the lower temperature zone (less than 2000 K) polymerization occurs resulting in formation of large, stable graphitic precursors, and in the high temperature zone (greater than 2000 K) polymer scission results in formation of short polymer chains/molecules. Simulations performed in the high temperature zone on the phenolic resin composites (with carbon nanotubes and carbon fibers) shows that the presence of interfaces had no substantial effect on the chain scission rate or the activation energy value for water formation.

  5. Carbon dioxide laser ablation with immediate autografting in a full-thickness porcine burn model.

    PubMed Central

    Glatter, R D; Goldberg, J S; Schomacker, K T; Compton, C C; Flotte, T J; Bua, D P; Greaves, K W; Nishioka, N S; Sheridan, R L

    1998-01-01

    OBJECTIVE: To compare the long-term clinical and histologic outcome of immediate autografting of full-thickness burn wounds ablated with a high-power continuous-wave CO2 laser to sharply débrided wounds in a porcine model. SUMMARY BACKGROUND DATA: Continuous-wave CO2 lasers have performed poorly as tools for burn excision because the large amount of thermal damage to viable subeschar tissues precluded successful autografting. However, a new technique, in which a high-power laser is rapidly scanned over the eschar, results in eschar vaporization without significant damage to underlying viable tissues, allowing successful immediate autografting. METHODS: Full-thickness paravertebral burn wounds measuring 36 cm2 were created on 11 farm swine. Wounds were ablated to adipose tissue 48 hours later using either a surgical blade or a 150-Watt continuous-wave CO2 laser deflected by an x-y galvanometric scanner that translated the beam over the tissue surface, removing 200 microm of tissue per scan. Both sites were immediately autografted and serially evaluated clinically and histologically for 180 days. RESULTS: The laser-treated sites were nearly bloodless. The mean residual thermal damage was 0.18+/-0.05 mm. The mean graft take was 96+/-11% in manual sites and 93+/-8% in laser sites. On postoperative day 7, the thickness of granulation tissue at the graft-wound bed interface was greater in laser-debrided sites. By postoperative day 180, the manual and laser sites were histologically identical. Vancouver scar assessment revealed no differences in scarring at postoperative day 180. CONCLUSIONS: Long-term scarring, based on Vancouver scar assessments and histologic evaluation, was equivalent at 6 months in laser-ablated and sharply excised sites. Should this technology become practical, the potential clinical implications include a reduction in surgical blood loss without sacrifice of immediate engraftment rates or long-term outcome. Images Figure 1. Figure 2. Figure 3

  6. Nanoparticle-assisted photothermal ablation of brain tumor in an orthotopic canine model

    NASA Astrophysics Data System (ADS)

    Schwartz, Jon A.; Shetty, Anil M.; Price, Roger E.; Stafford, R. Jason; Wang, James C.; Uthamanthil, Rajesh K.; Pham, Kevin; McNichols, Roger J.; Coleman, Chris L.; Payne, J. Donald

    2009-02-01

    We report on a pilot study demonstrating a proof of concept for the passive delivery of nanoshells to an orthotopic tumor where they induce a local, confined therapeutic response distinct from that of normal brain resulting in the photo-thermal ablation of canine Transmissible Venereal Tumor (cTVT) in a canine brain model. cTVT fragments grown in SCID mice were successfully inoculated in the parietal lobe of immuno-suppressed, mixed-breed hound dogs. A single dose of near-infrared absorbing, 150 nm nanoshells was infused intravenously and allowed time to passively accumulate in the intracranial tumors which served as a proxy for an orthotopic brain metastasis. The nanoshells accumulated within the intracranial cTVT suggesting that its neo-vasculature represented an interruption of the normal blood-brain barrier. Tumors were thermally ablated by percutaneous, optical fiber-delivered, near-infrared radiation using a 3.5 W average, 3-minute laser dose at 808 nm that selectively elevated the temperature of tumor tissue to 65.8+/-4.1ºC. Identical laser doses applied to normal white and gray matter on the contralateral side of the brain yielded sub-lethal temperatures of 48.6+/-1.1ºC. The laser dose was designed to minimize thermal damage to normal brain tissue in the absence of nanoshells and compensate for variability in the accumulation of nanoshells in tumor. Post-mortem histopathology of treated brain sections demonstrated the effectiveness and selectivity of the nanoshell-assisted thermal ablation.

  7. The laser ablation model development of glass substrate cutting assisted with the thermal fracture and ultrasonic mechanisms

    NASA Astrophysics Data System (ADS)

    Huang, Kuo-Cheng; Hsiao, Wen-Tse; Hwang, Chi-Hung; Lin, Ru-Li; Andrew Yeh, Jer-Liang

    2015-04-01

    This study presents three hybrid processing models for cutting a glass substrate, and compares their cutting speeds. The three models are (I) thermal fracture cutting technology (TFCT)-assisted laser ablation, (II) ultrasonic-assisted laser ablation, and (III) ultrasonic and TFCT-assisted laser ablation. In the experiment, a 12 W 355 nm Nd:YVO4 laser system, a 40 W CO2 laser and an ultrasonic transducer were used to cut 3 mm thick soda-lime glasses. Lasers and ultrasonic transducers were used as heat sources and vibration sources, respectively. Results show that the surface morphology of the soda-lime glass sheet depends on the processing models. After cutting, the surface and cross-sectional morphology of glass substrate were observed using a portable digital microscope and residual stresses were also evaluated thanks to a photoelasticity instrument.

  8. A meteor-ablation model of the sodium and potassium layers

    NASA Technical Reports Server (NTRS)

    Hunten, D. M.

    1981-01-01

    Recent results on meteor ablation are used as input to a model in which ablation (or evaporation) is the source and deposition on dust particles is the sink. The dust comes from recondensation of the rest of the meteor vapor. An excellent match is found to the observed characteristics of the sodium layer. It is argued that the high-latitude winter maximum of abundance (and layer height) is due to the much lower rate of ionization there and over the polar cap. The computations show the required factor of 4-5 and also match the height variation. To keep the ion density from being too large, downward electrodynamic transport at about 50 cm/sec must be invoked. The different behavior and low abundance of potassium require an additional sink. The one proposed is Penning ionization by metastable excited O2. Inherent in the model is that sodium and its compounds reside almost entirely on dust particles below 80 km. Large abundances in the free form at stratospheric heights are very unlikely and are not a good explanation of observed ambient ions.

  9. Contact dynamics math model

    NASA Technical Reports Server (NTRS)

    Glaese, John R.; Tobbe, Patrick A.

    1986-01-01

    The Space Station Mechanism Test Bed consists of a hydraulically driven, computer controlled six degree of freedom (DOF) motion system with which docking, berthing, and other mechanisms can be evaluated. Measured contact forces and moments are provided to the simulation host computer to enable representation of orbital contact dynamics. This report describes the development of a generalized math model which represents the relative motion between two rigid orbiting vehicles. The model allows motion in six DOF for each body, with no vehicle size limitation. The rotational and translational equations of motion are derived. The method used to transform the forces and moments from the sensor location to the vehicles' centers of mass is also explained. Two math models of docking mechanisms, a simple translational spring and the Remote Manipulator System end effector, are presented along with simulation results. The translational spring model is used in an attempt to verify the simulation with compensated hardware in the loop results.

  10. Heat Transfer And Vapor Dynamics Induced By Nanosecond Laser Ablation Of Titanium Target

    SciTech Connect

    Hamadi, F.; Amara, E. H.; Mezaoui, D.

    2008-09-23

    A numerical modelling describing a pulsed nanosecond laser interaction with a titanium target is presented, resulting in the study of the plume expansion in vacuum or in background gas, using the species transport model available in Fluent computational fluid dynamics code. The heat transfers in the solid target and the molten material are modeled using an enthalpy formulation for the solid-liquid phase changing. The effect of laser fluences is investigated, and results are presented as a function of time. Moreover, the plasma or the vapour dynamics is calculated by solving a set of Navier-Stokes equations. The plasma absorption by inverse Bremsstrahlung, the ionization states and the density profiles of the Titanium ions and electrons in the plume are interactively included in the Fluent calculation process by the mean of User Defined Functions (UDFs) used in order to take into account the specificity of our problem. The ionization is computed by solving the Saha-Eggert equation assuming local thermodynamic equilibrium (LTE) conditions.

  11. Studies on linear, nonlinear optical and excited state dynamics of silicon nanoparticles prepared by picosecond laser ablation

    SciTech Connect

    Hamad, Syed; Nageswara Rao, S. V. S.; Pathak, A. P.; Krishna Podagatlapalli, G.; Mounika, R.; Venugopal Rao, S. E-mail: soma-venu@uohyd.ac.in

    2015-12-15

    We report results from our studies on the fabrication and characterization of silicon (Si) nanoparticles (NPs) and nanostructures (NSs) achieved through the ablation of Si target in four different liquids using ∼2 picosecond (ps) pulses. The consequence of using different liquid media on the ablation of Si target was investigated by studying the surface morphology along with material composition of Si based NPs. The recorded mean sizes of these NPs were ∼9.5 nm, ∼37 nm, ∼45 nm and ∼42 nm obtained in acetone, water, dichloromethane (DCM) and chloroform, respectively. The generated NPs were characterized by selected area electron diffraction (SAED), high resolution transmission microscopy (HRTEM), Raman spectroscopic techniques and Photoluminescence (PL) studies. SAED, HRTEM and Raman spectroscopy data confirmed that the material composition was Si NPs in acetone, Si/SiO{sub 2} NPs in water, Si-C NPs in DCM and Si-C NPs in chloroform and all of them were confirmed to be polycrystalline in nature. Surface morphological information of the fabricated Si substrates was obtained using the field emission scanning electron microscopic (FESEM) technique. FESEM data revealed the formation of laser induced periodic surface structures (LIPSS) for the case of ablation in acetone and water while random NSs were observed for the case of ablation in DCM and chloroform. Femtosecond (fs) nonlinear optical properties and excited state dynamics of these colloidal Si NPs were investigated using the Z-scan and pump-probe techniques with ∼150 fs (100 MHz) and ∼70 fs (1 kHz) laser pulses, respectively. The fs pump-probe data obtained at 600 nm consisted of single and double exponential decays which were tentatively assigned to electron-electron collisional relaxation (<1 ps) and non-radiative transitions (>1 ps). Large third order optical nonlinearities (∼10{sup −14} e.s.u.) for these colloids have been estimated from Z-scan data at an excitation wavelength of 680 nm

  12. Studies on linear, nonlinear optical and excited state dynamics of silicon nanoparticles prepared by picosecond laser ablation

    NASA Astrophysics Data System (ADS)

    Hamad, Syed; Krishna Podagatlapalli, G.; Mounika, R.; Nageswara Rao, S. V. S.; Pathak, A. P.; Venugopal Rao, S.

    2015-12-01

    We report results from our studies on the fabrication and characterization of silicon (Si) nanoparticles (NPs) and nanostructures (NSs) achieved through the ablation of Si target in four different liquids using ˜2 picosecond (ps) pulses. The consequence of using different liquid media on the ablation of Si target was investigated by studying the surface morphology along with material composition of Si based NPs. The recorded mean sizes of these NPs were ˜9.5 nm, ˜37 nm, ˜45 nm and ˜42 nm obtained in acetone, water, dichloromethane (DCM) and chloroform, respectively. The generated NPs were characterized by selected area electron diffraction (SAED), high resolution transmission microscopy (HRTEM), Raman spectroscopic techniques and Photoluminescence (PL) studies. SAED, HRTEM and Raman spectroscopy data confirmed that the material composition was Si NPs in acetone, Si/SiO2 NPs in water, Si-C NPs in DCM and Si-C NPs in chloroform and all of them were confirmed to be polycrystalline in nature. Surface morphological information of the fabricated Si substrates was obtained using the field emission scanning electron microscopic (FESEM) technique. FESEM data revealed the formation of laser induced periodic surface structures (LIPSS) for the case of ablation in acetone and water while random NSs were observed for the case of ablation in DCM and chloroform. Femtosecond (fs) nonlinear optical properties and excited state dynamics of these colloidal Si NPs were investigated using the Z-scan and pump-probe techniques with ˜150 fs (100 MHz) and ˜70 fs (1 kHz) laser pulses, respectively. The fs pump-probe data obtained at 600 nm consisted of single and double exponential decays which were tentatively assigned to electron-electron collisional relaxation (<1 ps) and non-radiative transitions (>1 ps). Large third order optical nonlinearities (˜10-14 e.s.u.) for these colloids have been estimated from Z-scan data at an excitation wavelength of 680 nm suggesting that the

  13. Prostate cancer transrectal HIFU ablation: detection of local recurrences using T2-weighted and dynamic contrast-enhanced MRI.

    PubMed

    Rouvière, Olivier; Girouin, Nicolas; Glas, Ludivine; Ben Cheikh, Alexandre; Gelet, Albert; Mège-Lechevallier, Florence; Rabilloud, Muriel; Chapelon, Jean-Yves; Lyonnet, Denis

    2010-01-01

    The objective was to evaluate T2-weighted (T2w) and dynamic contrast-enhanced (DCE) MRI in detecting local cancer recurrences after prostate high-intensity focused ultrasound (HIFU) ablation. Fifty-nine patients with biochemical recurrence after prostate HIFU ablation underwent T2-weighted and DCE MRI before transrectal biopsy. For each patient, biopsies were performed by two operators: operator 1 (blinded to MR results) performed random and colour Doppler-guided biopsies ("routine biopsies"); operator 2 obtained up to three cores per suspicious lesion on MRI ("targeted biopsies"). Seventy-seven suspicious lesions were detected on DCE images (n = 52), T2w images (n = 2) or both (n = 23). Forty patients and 41 MR lesions were positive at biopsy. Of the 36 remaining MR lesions, 20 contained viable benign glands. Targeted biopsy detected more cancers than routine biopsy (36 versus 27 patients, p = 0.0523). The mean percentages of positive cores per patient and of tumour invasion of the cores were significantly higher for targeted biopsies (p < 0.0001). The odds ratios of the probability of finding viable cancer and viable prostate tissue (benign or malignant) at targeted versus routine biopsy were respectively 3.35 (95% CI 3.05-3.64) and 1.38 (95% CI 1.13-1.63). MRI combining T2-weighted and DCE images is a promising method for guiding post-HIFU biopsy towards areas containing recurrent cancer and viable prostate tissue.

  14. Macrophages loaded with gold nanoshells for photothermal ablation of glioma: An in vitro model

    NASA Astrophysics Data System (ADS)

    Makkouk, Amani Riad

    The current median survival of patients with glioblastoma multiforme (GBM), the most common type of glioma, remains at 14.6 months despite multimodal treatments (surgery, radiotherapy and chemotherapy). This research aims to study the feasibility of photothermal ablation of glioma using gold nanoshells that are heated upon laser irradiation at their resonance wavelength. The novelty of our approach lies in improving nanoshell tumor delivery by loading them in macrophages, which are known to be recruited to gliomas via tumor-released chemoattractive agents. Ferumoxides, superparamagnetic iron oxide (SPIO) nanoparticles, are needed as an additional macrophage load in order to visualize macrophage accumulation in the tumor with magnetic resonance imaging (MRI) prior to laser irradiation. The feasibility of this approach was studied in an in vitro model of glioma spheroids with the use of continuous wave (CW) laser light for ablation. The optimal loading of both murine and rat macrophages with Ferumoxides was determined using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Higher concentrations of SPIO were observed in rat macrophages, and the optimal concentration was chosen at 100 microg Fe/ml. Macrophages were found to be very sensitive to near infra-red (NIR) laser irradiation, and their use as vehicles was thus not expected to hinder the function of loaded nanoshells as tumor-ablating tools. The intracellular presence of gold nanoshells in macrophages was confirmed with TEM imaging. Next, the loading of both murine and rat macrophages with gold nanoshells was studied using UV/Vis spectrophotometry, where higher nanoshell uptake was found in rat macrophages. Incubation of loaded murine and rat macrophages with rat C-6 and human ACBT spheroids, respectively, resulted in their infiltration of the spheroids. Subsequent laser irradiation at 55 W/cm2 for 10 min and follow-up of spheroid average diameter size over 14 days post-irradiation showed that

  15. Mathematical Models Based on Transfer Functions to Estimate Tissue Temperature During RF Cardiac Ablation in Real Time

    PubMed Central

    Alba-Martínez, Jose; Trujillo, Macarena; Blasco-Gimenez, Ramon; Berjano, Enrique

    2012-01-01

    Radiofrequency cardiac ablation (RFCA) has been used to treat certain types of cardiac arrhythmias by producing a thermal lesion. Even though a tissue temperature higher than 50ºC is required to destroy the target, thermal mapping is not currently used during RFCA. Our aim was thus to develop mathematical models capable of estimating tissue temperature from tissue characteristics acquired or estimated at the beginning of the procedure (electrical conductivity, thermal conductivity, specific heat and density) and the applied voltage at any time. Biological tissue was considered as a system with an input (applied voltage) and output (tissue temperature), and so the mathematical models were based on transfer functions relating these variables. We used theoretical models based on finite element method to verify the mathematical models. Firstly, we solved finite element models to identify the transfer functions between the temperature at a depth of 4 mm and a constant applied voltage using a 7Fr and 4 mm electrode. The results showed that the relationships can be expressed as first-order transfer functions. Changes in electrical conductivity only affected the static gain of the system, while specific heat variations produced a change in the dynamic system response. In contrast, variations in thermal conductivity modified both the static gain and the dynamic system response. Finally, to assess the performance of the transfer functions obtained, we conducted a new set of computer simulations using a controlled temperature protocol and considering the temperature dependence of the thermal and electrical conductivities, i.e. conditions closer to those found in clinical use. The results showed that the difference between the values estimated from transfer functions and the temperatures obtained from finite element models was less than 4ºC, which suggests that the proposed method could be used to estimate tissue temperature in real time. PMID:22715345

  16. Dispersive effects in laser ablation plasmas

    NASA Astrophysics Data System (ADS)

    Irimiciuc, Ştefan Andrei; Agop, Maricel; Nica, Petru; Gurlui, Silviu; Mihăileanu, Doina; Toma, Ştefan; Focşa, Cristian

    2014-11-01

    The dynamics of transient plasmas generated by high-fluence nanosecond laser ablation has been investigated by recording the ionic current with a Langmuir probe. Systematic measurements have been carried out on a plasma produced in vacuum by Nd:YAG laser irradiation of a copper target. The temporal evolution of the ionic current for different fluences was investigated, revealing the presence of some periodic oscillations. A theoretical model is proposed in order to describe the nonlinear behavior of the expanding plasma by assuming that the motion curves of the ablated particles are fractals. The behaviors predicted by the proposed theoretical model are in good agreement with the experimental findings.

  17. A Gas-Surface Interaction Model For The Numerical Study Of High Temperature Flows Over Pyrolyzing Ablative Materials

    NASA Astrophysics Data System (ADS)

    Turchi, A.; Bianchi, D.; Nasuti, F.

    2011-05-01

    In the present study, modified surface mass and energy balances have been implemented in the ablative boundary condition of a two-dimensional full Navier-Stokes solver, to take into account the pyrolysis gas injection. A finite- rate ablation model is used, with steady-state ablation approximation to obtain the surface temperature. Hence, with this approximation, the conductive heat flux entering the wall can be directly computed without coupling with a solid conduction solver. Moreover, under this approximation, the pyrolysis gas mass flow rate is a known fraction of the char mass flow rate. Simulations of carbon-phenolic solid rocket motor nozzle have been performed to validate the model and to investigate the most uncertain parameters. Results show the influence of pyrolysis gas composition and ratio between mass fluxes of pyrolysis gas and of gaseous carbon, over the final erosion.

  18. Dynamic response of laser ablative shock waves from coated and uncoated amorphous Boron nanoparticles

    NASA Astrophysics Data System (ADS)

    Paturi, Prem Kiran; Chelikani, Leela; Pinnoju, Venkateshwarlu; Verma, Pankaj; Singh, Raja V.; Acrhem Collaboration; Hemrl Collaboration

    2015-06-01

    Nanoparticles (NP) improve the performance of solid rocket motors with increased burning rate and lower ignition threshold owing to their larger surface area. We present spatio-temporal evolution of laser ablative shock waves (LASWs) from compacted amorphous Boron (B) and Lithium Fluoride coated Boron (LiF-B) of 70-110nm sizes that were compacted to form pellets. Thickness of the LiF coating is 5.5 +/- 1 nm in LiF-B. Laser pulses from second harmonic of Nd:YAG laser (532 nm, 7 ns) are used to generate LASWs expanding in ambient air. The precise time of energy release from the pellets under extreme ablative pressures is studied using shadowgraphy with a temporal resolution of 1.5 ns. Different nature of the shock front (SF) following Sedov-Taylor theory, before and after detachment, indicated two specific time dependent stages of energy release. From the position of SF, velocity behind the SF, similar to that of exhaust velocity is measured. Specific impulse of 241 +/- 5 and 201 +/- 4 sec for LiF-B and B, respectively, at a delay of 0.8 μs from shock inducing laser pulse makes them potential candidates for laser based micro thruster applications. The work is supported by Defence Research and Developement Organization, India through Grants-in-Aid Program.

  19. Ablation dynamics and shock wave expansion during laser processing of CFRP with ultrashort laser pulses

    NASA Astrophysics Data System (ADS)

    Wiedenmann, Margit; Haist, Christoph; Freitag, Christian; Onuseit, Volkher; Weber, Rudolf; Graf, Thomas

    2014-03-01

    Carbon fibre reinforced plastics (CFRP) have a large potential in the automotive lightweight construction due to their low density and high mechanical stability. Compared with today's laser processing methods of metals the main issues in laser processing of CFRP are the very differing thermal, optical and mechanical properties of the components. To understand the process in detail, the ablation process of CFRP with ultrashort laser pulses was investigated. The shock wave and the vapor resulting from processing with single laser pulses were recorded. Shadow photography and luminescence photography with an ultra-high-speed camera was used to show the ablation process with a temporary resolution of up to 3 ns. The field of view was 250 μm × 250 μm. An ultrashort laser pulse with pulse duration of 4 ps and a wavelength of 800 nm was focused onto the workpiece. The energy content of the shock wave was calculated from the resulting images. The energy content of the shock wave was about 20 % of the incident energy and the speed of propagation of the shock wave was more than 2000 m/s. The high intensities in the range of 1013 W/cm2 lead to formation of a plasma plume which was clearly seen in the shadow photography images.

  20. Basic ablation phenomena during laser thrombolysis

    NASA Astrophysics Data System (ADS)

    Sathyam, Ujwal S.; Shearin, Alan; Prahl, Scott A.

    1997-05-01

    This paper presents studies of microsecond ablation phenomena that take place during laser thrombolysis. The main goals were to optimize laser parameters for efficient ablation, and to investigate the ablation mechanism. Gelatin containing an absorbing dye was used as the clot model. A parametric study was performed to identify the optimal wavelength, spot size, pulse energies, and repetition rate for maximum material removal. The minimum radiant exposures to achieve ablation at any wavelength were measured. The results suggest that most visible wavelengths were equally efficient at removing material at radiant exposures above threshold. Ablation was initiated at surface temperatures just above 100 degrees Celsius. A vapor bubble was formed during ablation. Less than 5% of the total pulse energy is coupled into the bubble energy. A large part of the delivered energy is unaccounted for and is likely released partly as acoustic transients from the vapor expansion and partly wasted as heat. The current laser and delivery systems may not be able to completely remove large clot burden that is sometimes encountered in heart attacks. However, laser thrombolysis may emerge as a favored treatment for strokes where the occlusion is generally smaller and rapid recanalization is of paramount importance. A final hypothesis is that laser thrombolysis should be done at radiant exposures close to threshold to minimize any damaging effects of the bubble dynamics on the vessel wall.

  1. In vivo analysis of Drosophila embryo developmental dynamics by femtosecond pulse-induced ablation and multimodal nonlinear microscopy

    NASA Astrophysics Data System (ADS)

    Supatto, Willy; Debarre, Delphine; Moulia, Bruno; Brouzes, Eric; Martin, Jean-Louis; Schanne-Klein, Marie-Claire; Farge, Emmanuel; Beaurepaire, Emmanuel

    2005-03-01

    Animal embryo development exhibits a complex ensemble of cell movements that are tightly regulated by developmental gene expression. It was proposed recently that mechanical factors may also play an important role during development. Investigating these dynamical processes is technically challenging and requires novel in vivo investigation methods. We show that multiphoton microscopy can be used for both perturbing and analyzing morphogenetic movements in vivo. (i) nonlinear microscopy is well adapted for the sustained imaging of early Drosophila embryos despite their highly scattering nature; (ii) femtosecond pulse-induced ablation can be used to process specific tissues in vivo. Combining this approach with multimodal microscopy (two-photon-excited fluorescence (2PEF) and third-harmonic generation (THG)), we report the successful quantitative modulation of morphogenetic movements in vivo. Our data provides insight to the issue of morphogenesis regulation.

  2. Spectroscopic modeling and characterization of a collisionally confined laser-ablated plasma plume.

    PubMed

    Sherrill, M E; Mancini, R C; Bailey, J; Filuk, A; Clark, B; Lake, P; Abdallah, J

    2007-11-01

    Plasma plumes produced by laser ablation are an established method for manufacturing the high quality stoichiometrically complex thin films used for a variety of optical, photoelectric, and superconducting applications. The state and reproducibility of the plasma close to the surface of the irradiated target plays a critical role in producing high quality thin films. Unfortunately, this dense plasma has historically eluded quantifiable characterization. The difficulty in modeling the plume formation arises in the accounting for the small amount of energy deposited into the target when physical properties of these exotic target materials are not known. In this work we obtain the high density state of the plasma plume through the use of an experimental spectroscopic technique and a custom spectroscopic model. In addition to obtaining detailed temperature and density profiles, issues regarding line broadening and opacity for spectroscopic characterization will be addressed for this unique environment.

  3. Charge-to-Mass Dispersion Methods in Knockout-Ablation Fragmentation Models

    NASA Astrophysics Data System (ADS)

    Townsend, Lawrence; Burton, Krista; de Wet, Wouter

    2014-09-01

    Breakup of high-energy heavy ions in nuclear collisions is an important process in space radiation transport, shielding and risk assessment since the secondary particles produced by these collisions have ranges greater than their parent nucleus, and are damaging to humans and spacecraft components. This work uses a quantum-mechanical optical potential knockout-ablation model to estimate these collision cross sections in order to investigate differences in isotope and element production cross sections as a result of utilizing two different models of charge-to mass ratios for the projectile prefragments produced by the abrasion/knockout process. One model commonly used, a hypergeometric model, assumes that the distribution of abraded nucleons is completely uncorrelated. However, it permits some unrealistic distributions, such as removing all neutrons in the knockout stage, while leaving all protons intact. Another model, developed for use with a classical geometric, clean-cut abrasion model, is based upon the zero point vibrations of the giant dipole resonance of the fragmenting nucleus. In this work we compare fragment production cross section predictions using the two charge dispersion models with published experimental data. Breakup of high-energy heavy ions in nuclear collisions is an important process in space radiation transport, shielding and risk assessment since the secondary particles produced by these collisions have ranges greater than their parent nucleus, and are damaging to humans and spacecraft components. This work uses a quantum-mechanical optical potential knockout-ablation model to estimate these collision cross sections in order to investigate differences in isotope and element production cross sections as a result of utilizing two different models of charge-to mass ratios for the projectile prefragments produced by the abrasion/knockout process. One model commonly used, a hypergeometric model, assumes that the distribution of abraded nucleons is

  4. The internal structure and dynamics of the railgun plasma armature between infinitely wide ablating rails

    NASA Astrophysics Data System (ADS)

    Frese, M. H.

    Conventional guns cannot achieve projectile velocities much greater than the sound speed in burned chemical propellants. Plasma armature railguns should not be subject to the same type of velocity limit. However, experiments indicate that there may be some other mechanism which can limit the velocity. A theory that accurately predicts the observed velocity limit could provide the insight necessary to raise or even lift that limit. As yet, there is no theoretical explanation drawn from physical first principles which predicts a limit to the achievable velocity. This report describes the first phase of an effort to use two-dimensional dynamic magnetohydrodynamic (MHD) simulation of the plasma motion in the bore to produce such an explanation. In this phase, MACH2, an Air Force two-dimensional MHD code has been quickly adapted to this problem. The principal goal of this effort was to demonstrate the feasibility and desirability of using MACH2 for railgun armature simulation. However, the simulations of plasma armatures described here are the most sophisticated models of the railgun arc presently available; they show the armature as a dynamic and developing plasma in a way never before seen. The goal could not have been more clearly achieved.

  5. Gamma Reaction History ablator areal density constraints upon correlated diagnostic modeling of National Ignition Facility implosion experiments

    SciTech Connect

    Cerjan, C. Sayre, D. B.; Landen, O. L.; Church, J. A.; Stoeffl, W.; Grafil, E. M.; Herrmann, H. W.; Hoffman, N. M.; Kim, Y.

    2015-03-15

    The inelastic neutron scattering induced γ-ray signal from {sup 12}C in an Inertial Confinement Fusion capsule is demonstrated to be an effective and general diagnostic for shell ablator areal density. Experimental acquisition of the time-integrated signal at 4.4 MeV using threshold detection from four gas Čerenkov cells provides a direct measurement of the {sup 12}C areal density near stagnation. Application of a three-dimensional isobaric static model of data acquired in a recent high neutron yield National Ignition Facility experimental campaign reveals two general trends: smaller remaining ablator mass at stagnation and higher shell density with increasing laser drive.

  6. Boundary conditions at the ablative walls in two-temperature modelling of thermal plasmas with reactive working gas

    NASA Astrophysics Data System (ADS)

    Pekker, Leonid; Murphy, Anthony B.

    2016-09-01

    In this paper, we propose a new set of boundary conditions at ablative hot walls with thermionic electron emission for two-temperature thermal arc models in which the temperature of electrons can deviate from the temperature of heavy particles,~{{T}\\text{e}}\

  7. Extended-Drude model to fit infrared conductivity cuprate laser-ablated films

    SciTech Connect

    Pessaud, S.; Sousa, D. de . Centre de Recherche sur la Physique des Hautes Temperatures); Lobo, R. ); Gervais, F. . Lab. d'Electrodynamique des Materiaux Avances)

    1998-12-20

    An extended-Drude model, implying a simple form for the self-energy function of the mobile charge-carrier response, has been applied to fitting the infrared and visible reflectivity spectra of simple cuprates. Excellent fits are obtained in a wide spectral range, from 4 meV to 4 eV, with a very restricted number of adjustable parameters. The optical conductivity obtained with this procedure is highly different from the Kramers-Kronig transformation of reflectivity spectra. The same procedure has been applied to characterize the infrared conductivity of multi-target laser-ablated films built via intergrowth of YBa[sub 2]Cu[sub 3]O[sub 7] and MCuO[sub 2] (M = Ca, Sr).

  8. Modeling Soil Freezing Dynamics

    NASA Astrophysics Data System (ADS)

    Flerchinger, G. N.; Seyfried, M. S.; Hardegree, S. P.

    2002-12-01

    Seasonally frozen soil strongly influences runoff and erosion on large areas of land around the world. In many areas, rain or snowmelt on seasonally frozen soil is the single leading cause of severe runoff and erosion events. As soils freeze, ice blocks the soil pores, greatly diminishing the permeability of the soil. This is aggravated by the tendency of water to migrate to the freezing front, causing elevated ice content and frost heave. Freezing and thawing of the soil are controlled by the complex interactions of heat and water transfer at the soil surface governed by meteorological and environmental conditions at the soil-atmosphere interface. Soil freezing dynamics including liquid water content, infiltration, and runoff simulated by the Simultaneous Heat and Water (SHAW) Model were tested at three field locations in southwest Idaho. Sites included: three soil types at the Orchard Field Test Site; bare and sagebrush-covered runoff plots at the Lower Sheep Creek site on the Reynolds Creek Experimental Watershed; and runoff plots on steep mountainous slopes on the Boise Front. Detailed simulations of soil freezing and thawing were conducted specifically to examine the dynamics of liquid water content during freezing and thawing. Freezing/thawing processes, including liquid water content and runoff, were simulated well.

  9. Ascl3 knockout and cell ablation models reveal complexity of salivary gland maintenance and regeneration.

    PubMed

    Arany, Szilvia; Catalán, Marcelo A; Roztocil, Elisa; Ovitt, Catherine E

    2011-05-15

    Expression of the transcription factor, Ascl3, marks a population of adult progenitor cells, which can give rise to both acinar and duct cell types in the murine salivary glands. Using a previously reported Ascl3(EGFP-Cre/+) knock-in strain, we demonstrate that Ascl3-expressing cells represent a molecularly distinct, and proliferating population of progenitor cells located in salivary gland ducts. To investigate both the role of the Ascl3 transcription factor, and the role of the cells in which it is expressed, we generated knockout and cell-specific ablation models. Ascl3 knockout mice develop smaller salivary glands than wild type littermates, but secrete saliva normally. They display a lower level of cell proliferation, consistent with their smaller size. In the absence of Ascl3, the cells maintain their progenitor function and continue to generate both acinar and duct cells. To directly test the role of the progenitor cells, themselves, in salivary gland development and regeneration, we used Cre-activated expression of diphtheria toxin (DTA) in the Ascl3-expressing (Ascl3+) cell population, resulting in specific cell ablation of Ascl3+ cells. In the absence of the Ascl3+ progenitor cells, the mice developed morphologically normal, albeit smaller, salivary glands able to secrete saliva. Furthermore, in a ductal ligation model of salivary gland injury, the glands of these mice were able to regenerate acinar cells. Our results indicate that Ascl3+ cells are active proliferating progenitors, but they are not the only precursors for salivary gland development or regeneration. We conclude that maintenance of tissue homeostasis in the salivary gland must involve more than one progenitor cell population.

  10. Gas dynamics modeling of the HYLIFE-II reactor

    SciTech Connect

    Jantzen, C.

    1995-08-01

    Gas dynamics in the IFE reactor, HYLIFE-II is modeled using the code, TSUNAMI. This code is a 2-D shock-solver that uses the Godunov method with operator splitting. Results from a cylindrically symmetric simulation indicate an initial, low density, burst of high energy particles enters the final focus transport lens within 40 microseconds after the blast, much faster than the proposed 1 millisecond shutter closing time. After approximately 100 microseconds the chamber debris flux levels off to one eighth its peak value and maintains this intensity until the shutter closes. Although initial protective jet ablation is considered, neither secondary radiation nor condensation are modeled. Therefore results are conservative.

  11. Measuring and Modeling Snow Accumulation, Movement, and Ablation in Colorado Shrublands

    NASA Astrophysics Data System (ADS)

    Hiemstra, C. A.; Liston, G. E.; Strack, J. E.; Elder, K.

    2004-12-01

    Basin shrublands, featuring Artemisia tridentata and Sarcobatus vermiculatus shrubs accompanied by various graminoids, are widespread constituents of intermountain western U.S. landscapes. These shrublands are characterized by spatially heterogeneous winter snow covers interrupted by transient melting periods. The spatial heterogeneity of snow in shrubland landscapes is determined by interactions among topography, wind, net radiation, and vegetation structure (shrub vs. graminoid canopy dominants). Transient melting periods are typically produced by intermittent warm and dry phases where snow melts over much of the landscape, especially in wind-scoured grassy areas where snow depths are relatively shallow. Because snow is an important factor in the annual water and energy budgets of shrublands, it is important to quantify and understand snow accumulation, movement, and ablation processes in these landscapes. We employed snow depth observations and a snow evolution modeling system (SnowModel) to quantify and simulate snow depths in North Park, an intermountain basin in Colorado. Observations and simulations focused on a 0.25 km2 study area centered on a 34 m tall meteorological tower deployed for the FLuxes Over Snow Surfaces (FLOSS) project (http://www.atd.ucar.edu/rtf/projects/floss/). Snow observations were measured along a series of transects, extending 400-600 m upwind of the tower, every 10 days from late December 2002 to late March 2003. The transects were designed to capture snow characteristics within shrub and graminoid cover types. Further, observations were used to parameterize and validate SnowModel. Hourly model simulations were performed from 1 October 2002 to 1 April 2003 using topographic, meteorological, and vegetation distribution data for the domain. Observed and modeled snow characteristics are described. Over 30,000 snow depth observations were collected during the field season. Snow cover in graminoid-dominated areas was shallow, less variable

  12. Distributed modeling of ablation (1996–2011) and climate sensitivity on the glaciers of Taylor Valley, Antarctica

    DOE PAGES

    Hoffman, Matthew J.; Fountain, Andrew G.; Liston, Glen E.

    2016-02-24

    Here, the McMurdo Dry Valleys of Antarctica host the coldest and driest ecosystem on Earth, which is acutely sensitive to the availability of water coming from glacial runoff. We modeled the spatial variability in ablation and assessed climate sensitivity of the glacier ablation zones using 16 years of meteorological and surface mass-balance observations collected in Taylor Valley. Sublimation was the primary form of mass loss over much of the ablation zones, except for near the termini where melt, primarily below the surface, dominated. Microclimates in ~10 m scale topographic basins generated melt rates up to ten times higher than overmore » smooth glacier surfaces. In contrast, the vertical terminal cliffs on the glaciers can have higher or lower melt rates than the horizontal surfaces due to differences in incoming solar radiation. The model systematically underpredicted ablation for the final 5 years studied, possibly due to an increase of windblown sediment. Surface mass-balance sensitivity to temperature was ~–0.02 m w.e. K–1, which is among the smallest magnitudes observed globally. We also identified a high sensitivity to ice albedo, with a decrease of 0.02 having similar effects as a 1 K increase in temperature, and a complex sensitivity to wind speed.« less

  13. Modelling of Indirect Laser-induced Thin-film Ablation of Epoxy for Local Exposing of Carbon Fibers

    NASA Astrophysics Data System (ADS)

    Emonts, Michael; Fischer, Kai; Schmitt, Stefan; Schares, Richard Ludwig

    Laser radiation is used as enabling technology for intrinsic joining of high-strength CFRP laminates and fiber-reinforced thermoplastic injection moulding compounds by exposure of surface-near carbon fibers. Short-pulsed NIR laser sources represent an acceptable compromise with respect to ablation performance, remote process capability by use of compact 3D scanner and the capability for closed-loop process control. However, using such a laser source means also minimizing heat-affected zones (HAZ). Based on literature research about laser ablation of thin metal films, heat flow at CFRP and thermo-mechanical behavior in FRP by pyrolysis, an analytical model was generated for thin-film ablation of cured epoxy resins at the surface of CFRP laminates by lift-off of resin chips. A comparison between simulation and experimental results confirms the capability of the model to predict the exposure area and the HAZ with deviations below 15%. Threshold fluences for the HAZ (>1 J/cm2) and the resin ablation (>3 J/cm2) have been confirmed.

  14. Dynamics of femto- and nanosecond laser ablation plumes investigated using optical emission spectroscopy

    SciTech Connect

    Verhoff, B.; Harilal, S. S.; Freeman, J. R.; Diwakar, P. K.; Hassanein, A.

    2012-11-01

    We investigated the spatial and temporal evolution of temperature and electron density associated with femto- and nanosecond laser-produced plasmas (LPP) from brass under similar laser fluence conditions. For producing plasmas, brass targets were ablated in vacuum employing pulses either from a Ti:Sapphire ultrafast laser (40 fs, 800 nm) or from a Nd:YAG laser (6 ns, 1064 nm). Optical emission spectroscopy is used to infer the density and temperature of the plasmas. The electron density (n{sub e}) was estimated using Stark broadened profiles of isolated lines while the excitation temperature (T{sub exc}) was estimated using the Boltzmann plot method. At similar fluence levels, continuum and ion emission are dominant in ns LPP at early times (<50 ns) followed by atomic emission, while the fs LPP provided an atomic plume throughout its visible emission lifetime. Though both ns and fs laser-plasmas showed similar temperatures ({approx}1 eV), the fs LPP is found to be significantly denser at shorter distances from the target surface as well as at early phases of its evolution compared to ns LPP. Moreover, the spatial extension of the plume emission in the visible region along the target normal is larger for fs LPP in comparison with ns LPP.

  15. Percutaneous Irreversible Electroporation Lung Ablation: Preliminary Results in a Porcine Model

    SciTech Connect

    Deodhar, Ajita; Monette, Sebastien; Single, Gordon W.; Hamilton, William C.; Thornton, Raymond H.; Sofocleous, Constantinos T.; Maybody, Majid; Solomon, Stephen B.

    2011-12-15

    Objective: Irreversible electroporation (IRE) uses direct electrical pulses to create permanent 'pores' in cell membranes to cause cell death. In contrast to conventional modalities, IRE has a nonthermal mechanism of action. Our objective was to study the histopathological and imaging features of IRE in normal swine lung. Materials and Methods: Eleven female swine were studied for hyperacute (8 h), acute (24 h), subacute (96 h), and chronic (3 week) effects of IRE ablation in lung. Paired unipolar IRE applicators were placed under computed tomography (CT) guidance. Some applicators were deliberately positioned near bronchovascular structures. IRE pulse delivery was synchronized with the cardiac rhythm only when ablation was performed within 2 cm of the heart. Contrast-enhanced CT scan was performed immediately before and after IRE and at 1 and 3 weeks after IRE ablation. Representative tissue was stained with hematoxylin and eosin for histopathology. Results: Twenty-five ablations were created: ten hyperacute, four acute, and three subacute ablations showed alveolar edema and necrosis with necrosis of bronchial, bronchiolar, and vascular epithelium. Bronchovascular architecture was maintained. Chronic ablations showed bronchiolitis obliterans and alveolar interstitial fibrosis. Immediate post-procedure CT images showed linear or patchy density along the applicator tract. At 1 week, there was consolidation that resolved partially or completely by 3 weeks. Pneumothorax requiring chest tube developed in two animals; no significant cardiac arrhythmias were noted. Conclusion: Our preliminary porcine study demonstrates the nonthermal and extracellular matrix sparing mechanism of action of IRE. IRE is a potential alternative to thermal ablative modalities.

  16. Measurement of Intrahepatic Pressure during Microwave Ablation in an Ex Vivo Bovine Liver Model

    PubMed Central

    Kim, Hae Jin; Rhim, Hyunchul; Lee, Min Woo; Jeong, Woo Kyoung

    2015-01-01

    Background/Aims We experimented with different ablation methods and two types of microwave antennas to determine whether microwave ablation (MWA) increases intrahepatic pressure and to identify an MWA protocol that avoids increasing intrahepatic pressure. Methods MWA was performed using either a single-step standard ablation or a stepwise increment ablation paired with either a 16-gauge (G) 2-cm antenna or a 14G 4-cm antenna. We compared the maximum pressures and total ablation volumes. Results The mean maximum intrahepatic pressures and ablation volumes were as follows: 16G single-step: 37±33.4 mm Hg and 4.63 cm3; 16G multistep: 31±18.7 mm Hg and 3.75 cm3; 14G single-step: 114±45.4 mm Hg and 15.33 cm3; and 14G multistep: 106±43.8 mm Hg and 10.98 cm3. The intrahepatic pressure rose during MWA, but there were no statistically significant differences between the single and multistep methods when the same gauge antennae were used. The total ablation volume was different only in the 14G groups (p<0.05). Conclusions We demonstrated an increase in intrahepatic pressure during MWA. The multistep method may be used to prevent increased intrahepatic pressure after applying the proper power. PMID:25963083

  17. Calibration of a distributed ablation model for Zhadang Glacier, Tibetan Plateau,using a time lapse camera system

    NASA Astrophysics Data System (ADS)

    Schneider, C.; Huintjes, E.; Bhattacharya, A.; Sauter, T.; Yang, W.; Bolch, T.; Pieczonka, T.; Maussion, F.; Kang, S.; Buchroithner, M.; Scherer, D.; Yao, T.

    2011-12-01

    A 1-dimensional energy balance model for calculation of snow melt including sub-surface refreezing has been applied in a simplified version for distributed ablation modeling on Zhadang Glacier, Nyainqentanglha Range, Tibetan Plateau. The model includes a distributed computation of short-wave radiation on a digital elevation model. Reduction of short-wave radiation due to cloud cover has been accounted for by comparing calculated radiation against measurements at an automatic weather station (AWS) on the glacier. Air temperature was distributed using the lapse rate as derived from AWS measurements in different altitudes along the Zhadang Valley. Specific humidity and wind speed were assumed to be spatially invariant. Also, ice temperature in spring at 10 m depth was assumed to be equal all over the glacier. In the same way, accumulation as measured at the AWS using an ultra-sonic ranging system was assumed to be the same for the whole glacier surface. Snow accumulation was corrected using daily imagery obtained from an automatic time lapse camera system installed outside the glacier. The same time series of pictures allows for detailed spatial and temporal observation of the transient snow line. Gaps in AWS data are filled by downscaling of the output of WRF numerical atmospheric model output to the AWS location on the glacier. The runs of the ablation model are initialized using spatially distributed snow depth measured at a series of ablation stakes on the glacier. From the model results the location of the transient snow line can be precisely located. The findings are compared to the transient snow line as derived from the picture series. Besides the possibility of post-calibrating the spatially distributed ablation model, the results of this approach also allow for identifying further relevant spatial processes that are not yet considered.

  18. Deviation from threshold model in ultrafast laser ablation of graphene at sub-micron scale

    SciTech Connect

    Gil-Villalba, A.; Xie, C.; Salut, R.; Furfaro, L.; Giust, R.; Jacquot, M.; Lacourt, P. A.; Dudley, J. M.; Courvoisier, F.

    2015-08-10

    We investigate a method to measure ultrafast laser ablation threshold with respect to spot size. We use structured complex beams to generate a pattern of craters in CVD graphene with a single laser pulse. A direct comparison between beam profile and SEM characterization allows us to determine the dependence of ablation probability on spot-size, for crater diameters ranging between 700 nm and 2.5 μm. We report a drastic decrease of ablation probability when the crater diameter is below 1 μm which we interpret in terms of free-carrier diffusion.

  19. Modeling of plasma distortions by laser-induced ablation spectroscopy (LIAS) and implications for the interpretation of LIAS measurements

    NASA Astrophysics Data System (ADS)

    Tokar, M. Z.; Gierse, N.; Philipps, V.; Samm, U.

    2015-09-01

    For the interpretation of the line radiation observed from laser induced ablation spectroscopy (LIAS) such parameters as the density and temperature of electrons within very compact clouds of atoms and singly charged ions of ablated material have to be known. Compared to the local plasma conditions prior to the laser pulse, these can be strongly changed during LIAS since new electrons are generated by the ionisation of particles ejected from the irradiated target. Because of their transience and spatial inhomogeneity it is technically difficult to measure disturbances induced in the plasma by LIAS. To overcome this uncertainty a numerical model has been elaborated, providing a self-consistent description for the spreading of ablated particles and accompanying modifications in the plasma. The results of calculations for LIAS performed on carbon-containing targets in Ohmic and additionally heated discharges in the tokamak TEXTOR are presented. Due to the increase in the electron density the ‘ionisation per photon’ ratio, S/XB factor, is significantly enhanced compared to unperturbed plasma conditions. The impact of the amount of material ablated and of the plasma conditions before LIAS on the level of the S/XB-enhancement is investigated.

  20. Radio-frequency ablation-based studies on VX2rabbit models for HCC treatment.

    PubMed

    Bimonte, Sabrina; Leongito, Maddalena; Piccirillo, Mauro; de Angelis, Cristina; Pivonello, Claudia; Granata, Vincenza; Izzo, Francesco

    2016-01-01

    Hepatocellular carcinoma (HCC) is the fifth most frequent cancer worldwide with high morbidity, mortality and increasing incidence. It is of note that the main curative therapies for HCC are hepatic resection and transplantation although the majority of patients at the time of presentation are not eligible for resection or orthotopic liver transplantation (OLT) due to the underlying cirrhosis. Currently, a variety of loco-regional therapies, including radiofrequency ablation (RFA), percutaneous ethanol injection (PEI), microwave coagulation therapy (MCT), transarterial chemoembolization (TACE) and others, have been developed as alternative treatment options for HCC. Among these techniques, RFA is currently the most widely used treatment, due to its several advantages, such as safety and efficacy. To date, the effectiveness of RFA for HCC is reduced by the presence of residual tumor as a consequence of insufficient treatment. In order to ameliorate the effects of RFA on HCC, several in vivo studies, have been performed on its application as single or in combination treatment with drugs or others loco-regional therapies, by using rabbit VX2 liver model. This represents an ideal model of liver cancers and is widely used for imaging and other experimental studies due to the rapid growth of these tumors and their similarity to human hepatocellular carcinoma. In order to elucidate the therapeutic potential of RFA with adjuvant treatments for HCC, we reviewed the latest findings on the RFA-based studies in rabbit VX2 hepatocarcinoma models. PMID:27525037

  1. Brazilian red propolis attenuates hypertension and renal damage in 5/6 renal ablation model.

    PubMed

    Teles, Flávio; da Silva, Tarcilo Machado; da Cruz Júnior, Francisco Pessoa; Honorato, Vitor Hugo; de Oliveira Costa, Henrique; Barbosa, Ana Paula Fernandes; de Oliveira, Sabrina Gomes; Porfírio, Zenaldo; Libório, Alexandre Braga; Borges, Raquel Lerner; Fanelli, Camilla

    2015-01-01

    The pathogenic role of inflammation and oxidative stress in chronic kidney disease (CKD) is well known. Anti-inflammatories and antioxidant drugs has demonstrated significant renoprotection in experimental nephropathies. Moreover, the inclusion of natural antioxidants derived from food and herbal extracts (such as polyphenols, curcumin and lycopene) as an adjuvant therapy for slowing CKD progression has been largely tested. Brazilian propolis is a honeybee product, whose anti-inflammatory, antimicrobial and antioxidant effects have been widely shown in models of sepsis, cancer, skin irritation and liver fibrosis. Furthermore, previous studies demonstrated that this compound promotes vasodilation and reduces hypertension. However, potential renoprotective effects of propolis in CKD have never been investigated. The aim of this study was to evaluate the effects of a subtype of Brazilian propolis, the Red Propolis (RP), in the 5/6 renal ablation model (Nx). Adult male Wistar rats underwent Nx and were divided into untreated (Nx) and RP-treated (Nx+RP) groups, after 30 days of surgery; when rats already exhibited marked hypertension and proteinuria. Animals were observed for 90 days from the surgery day, when Nx+RP group showed significant reduction of hypertension, proteinuria, serum creatinine retention, glomerulosclerosis, renal macrophage infiltration and oxidative stress, compared to age-matched untreated Nx rats, which worsened progressively over time. In conclusion, RP treatment attenuated hypertension and structural renal damage in Nx model. Reduction of renal inflammation and oxidative stress could be a plausible mechanism to explain this renoprotection. PMID:25607548

  2. Development of a Swine Benign Biliary Stricture Model Using Endoscopic Biliary Radiofrequency Ablation.

    PubMed

    Park, Jin Seok; Jeong, Seok; Kim, Joon Mee; Park, Sang Soon; Lee, Don Haeng

    2016-09-01

    The large animal model with benign biliary stricture (BBS) is essential to undergo experiment on developing new devices and endoscopic treatment. This study conducted to establish a clinically relevant porcine BBS model by means of endobiliary radiofrequency ablation (RFA). Endoscopic retrograde cholangiography (ERC) was performed on 12 swine. The animals were allocated to three groups (60, 80, and 100 W) according to the electrical power level of RFA electrode. Endobiliary RFA was applied to the common bile duct for 60 seconds using an RFA catheter that was endoscopically inserted. ERC was repeated two and four weeks, respectively, after the RFA to identify BBS. After the strictures were identified, histologic evaluations were performed. On the follow-up ERC two weeks after the procedure, a segmental bile duct stricture was observed in all animals. On microscopic examination, severe periductal fibrosis and luminal obliteration with transmural inflammation were demonstrated. Bile duct perforations occurred in two pigs (100 W, n = 1; 80 W, n = 1) but there were no major complications in the 60 W group. The application of endobiliary RFA with 60 W electrical power resulted in a safe and reproducible swine model of BBS. PMID:27510388

  3. Modeling and experiments of x-ray ablation of National Ignition Facility first wall materials

    SciTech Connect

    Anderson, A.T.; Burnham, A.K.; Tobin, M.T.; Peterson, P.F.

    1996-06-04

    This paper discusses results of modeling and experiments on the x-ray response of selected materials relevant to NIF target chamber design. X-ray energy deposition occurs in such small characteristic depths (on the order of a micron) that thermal conduction and hydrodynamic motion significantly affect the material response, even during the typical 10-ns pulses. The finite-difference ablation model integrates four separate processes: x-ray energy deposition, heat conduction, hydrodynamics, and surface vaporization. Experiments have been conducted at the Nova laser facility in Livermore on response of various materials to NIF-relevant x-ray fluences. Fused silica, Si nitride, B carbide, B, Si carbide, C, Al2O3, and Al were tested. Response was diagnosed using post-shot examinations of the surfaces with SEM and atomic force microscopes. Judgements were made about the dominant removal mechanisms for each material; relative importances of these processes were also studied with the x-ray response model.

  4. Brazilian Red Propolis Attenuates Hypertension and Renal Damage in 5/6 Renal Ablation Model

    PubMed Central

    Teles, Flávio; da Silva, Tarcilo Machado; da Cruz Júnior, Francisco Pessoa; Honorato, Vitor Hugo; de Oliveira Costa, Henrique; Barbosa, Ana Paula Fernandes; de Oliveira, Sabrina Gomes; Porfírio, Zenaldo; Libório, Alexandre Braga; Borges, Raquel Lerner; Fanelli, Camilla

    2015-01-01

    The pathogenic role of inflammation and oxidative stress in chronic kidney disease (CKD) is well known. Anti-inflammatories and antioxidant drugs has demonstrated significant renoprotection in experimental nephropathies. Moreover, the inclusion of natural antioxidants derived from food and herbal extracts (such as polyphenols, curcumin and lycopene) as an adjuvant therapy for slowing CKD progression has been largely tested. Brazilian propolis is a honeybee product, whose anti-inflammatory, antimicrobial and antioxidant effects have been widely shown in models of sepsis, cancer, skin irritation and liver fibrosis. Furthermore, previous studies demonstrated that this compound promotes vasodilation and reduces hypertension. However, potential renoprotective effects of propolis in CKD have never been investigated. The aim of this study was to evaluate the effects of a subtype of Brazilian propolis, the Red Propolis (RP), in the 5/6 renal ablation model (Nx). Adult male Wistar rats underwent Nx and were divided into untreated (Nx) and RP-treated (Nx+RP) groups, after 30 days of surgery; when rats already exhibited marked hypertension and proteinuria. Animals were observed for 90 days from the surgery day, when Nx+RP group showed significant reduction of hypertension, proteinuria, serum creatinine retention, glomerulosclerosis, renal macrophage infiltration and oxidative stress, compared to age-matched untreated Nx rats, which worsened progressively over time. In conclusion, RP treatment attenuated hypertension and structural renal damage in Nx model. Reduction of renal inflammation and oxidative stress could be a plausible mechanism to explain this renoprotection. PMID:25607548

  5. Laser-Ablated Plasma Dynamics Study For Sm{sub 1-x}Nd{sub x}NiO{sub 3} Thin Films Deposition

    SciTech Connect

    Lafane, S.; Kerdja, T.; Abdelli-Messaci, S.; Malek, S.; Maaza, M.

    2008-09-23

    The expansion dynamics of Sm{sub 1-x}Nd{sub x}NiO{sub 3} excimer laser ablation plume in background oxygen atmosphere has been investigated using a fast ICCD imaging. The laser fluence was fixed at 2 J{center_dot}cm{sup -2} and the surrounding ambient gas pressure was varied from vacuum to 50 mbars. The imaging data is used to create position--time plots of the luminous front at several background oxygen pressures. The plume behaviour is found influenced by the gas pressure. In earlier time, the expansion is almost linear independently of the background gas pressure used, and then as time evolves, the plume expansion is well characterized by a spherical shock wave model and at later times, the plume is decelerated and comes to rest, so the drag force model is a good approximation to this regime of expansion. Plume splitting into fast and slow components was another feature observed at some distances depending on the oxygen background pressure. The optimal target-substrate distance for thin film deposition has been estimated.

  6. Dynamic absorption and scattering of water and hydrogel during high-repetition-rate (>100 MHz) burst-mode ultrafast-pulse laser ablation.

    PubMed

    Qian, Zuoming; Covarrubias, Andrés; Grindal, Alexander W; Akens, Margarete K; Lilge, Lothar; Marjoribanks, Robin S

    2016-06-01

    High-repetition-rate burst-mode ultrafast-laser ablation and disruption of biological tissues depends on interaction of each pulse with the sample, but under those particular conditions which persist from previous pulses. This work characterizes and compares the dynamics of absorption and scattering of a 133-MHz repetition-rate, burst-mode ultrafast-pulse laser, in agar hydrogel targets and distilled water. The differences in energy partition are quantified, pulse-by-pulse, using a time-resolving integrating-sphere-based device. These measurements reveal that high-repetition-rate burst-mode ultrafast-laser ablation is a highly dynamical process affected by the persistence of ionization, dissipation of plasma plume, neutral material flow, tissue tensile strength, and the hydrodynamic oscillation of cavitation bubbles. PMID:27375948

  7. Dynamic absorption and scattering of water and hydrogel during high-repetition-rate (>100 MHz) burst-mode ultrafast-pulse laser ablation

    PubMed Central

    Qian, Zuoming; Covarrubias, Andrés; Grindal, Alexander W.; Akens, Margarete K.; Lilge, Lothar; Marjoribanks, Robin S.

    2016-01-01

    High-repetition-rate burst-mode ultrafast-laser ablation and disruption of biological tissues depends on interaction of each pulse with the sample, but under those particular conditions which persist from previous pulses. This work characterizes and compares the dynamics of absorption and scattering of a 133-MHz repetition-rate, burst-mode ultrafast-pulse laser, in agar hydrogel targets and distilled water. The differences in energy partition are quantified, pulse-by-pulse, using a time-resolving integrating-sphere-based device. These measurements reveal that high-repetition-rate burst-mode ultrafast-laser ablation is a highly dynamical process affected by the persistence of ionization, dissipation of plasma plume, neutral material flow, tissue tensile strength, and the hydrodynamic oscillation of cavitation bubbles. PMID:27375948

  8. Non-linear dual-phase-lag model for analyzing heat transfer phenomena in living tissues during thermal ablation.

    PubMed

    Kumar, P; Kumar, Dinesh; Rai, K N

    2016-08-01

    In this article, a non-linear dual-phase-lag (DPL) bio-heat transfer model based on temperature dependent metabolic heat generation rate is derived to analyze the heat transfer phenomena in living tissues during thermal ablation treatment. The numerical solution of the present non-linear problem has been done by finite element Runge-Kutta (4,5) method which combines the essence of Runge-Kutta (4,5) method together with finite difference scheme. Our study demonstrates that at the thermal ablation position temperature predicted by non-linear and linear DPL models show significant differences. A comparison has been made among non-linear DPL, thermal wave and Pennes model and it has been found that non-linear DPL and thermal wave bio-heat model show almost same nature whereas non-linear Pennes model shows significantly different temperature profile at the initial stage of thermal ablation treatment. The effect of Fourier number and Vernotte number (relaxation Fourier number) on temperature profile in presence and absence of externally applied heat source has been studied in detail and it has been observed that the presence of externally applied heat source term highly affects the efficiency of thermal treatment method. PMID:27503734

  9. Non-linear dual-phase-lag model for analyzing heat transfer phenomena in living tissues during thermal ablation.

    PubMed

    Kumar, P; Kumar, Dinesh; Rai, K N

    2016-08-01

    In this article, a non-linear dual-phase-lag (DPL) bio-heat transfer model based on temperature dependent metabolic heat generation rate is derived to analyze the heat transfer phenomena in living tissues during thermal ablation treatment. The numerical solution of the present non-linear problem has been done by finite element Runge-Kutta (4,5) method which combines the essence of Runge-Kutta (4,5) method together with finite difference scheme. Our study demonstrates that at the thermal ablation position temperature predicted by non-linear and linear DPL models show significant differences. A comparison has been made among non-linear DPL, thermal wave and Pennes model and it has been found that non-linear DPL and thermal wave bio-heat model show almost same nature whereas non-linear Pennes model shows significantly different temperature profile at the initial stage of thermal ablation treatment. The effect of Fourier number and Vernotte number (relaxation Fourier number) on temperature profile in presence and absence of externally applied heat source has been studied in detail and it has been observed that the presence of externally applied heat source term highly affects the efficiency of thermal treatment method.

  10. Radiofrequency Ablation (RFA): Development of a Flow Model for Bovine Livers for Extensive Bench Testing

    SciTech Connect

    Lubienski, Andreas Bitsch, Rudi G.; Lubienski, Katrin; Kauffmann, Guenter; Duex, Markus

    2006-12-15

    Purpose. To develop a flow model for bovine livers for extensive bench testing of technical improvements or procedure-related developments of radiofrequency ablation excluding animal experiments. Methods. The perfusion of bovine livers directly from the slaughterhouse was simulated in a liver perfusion tank developed for the experimental work. The liver perfusion medium used was a Tyrode solution prepared in accordance with physiologic criteria (as for liver transplants) which was oxygenated by an oxygenator and heated to 36.5 deg. C. Portal vein circulation was regulated via a flow- and pressure-controlled pump and arterial circulation using a dialysis machine. Flow rate and pressure were adjusted as for the physiology of a human liver converted to bovine liver conditions. The fluid discharged from the liver was returned into the perfusion system through the vena cava. Extendable precision swivel arms with the radiofrequency probe attached were mounted on the liver perfusion tank. RFA was conducted with the RF3000 generator and a 2 cm LeVeen needle (Boston Scientific, Ratingen, Germany) in a three-dimensional grid for precise localization of the generated thermolesions. Results. Four bovine livers weighing 8.4 {+-} 0.4 kg each were prepared, connected to the perfusion system, and consecutively perfused for the experiments. Mean arterial flow was 569 {+-} 43 ml/min, arterial pressure 120 mmHg, portovenous flow 1440 {+-} 305 ml/min, and portal pressure 10 mmHg. Macroscopic evaluation after the experiments revealed no thrombi within the hepatic vessels. A total of 136 RF thermolesions were generated with an average number of 34 per liver. Mean RF duration was 2:59 {+-} 2:01 min:sec with an average baseline impedance of 28.2 {+-} 3.4 ohms. The mean diameter of the thermolesions along the puncture channel was 22.98 {+-} 4.34 mm and perpendicular to the channel was 23.27 {+-} 4.82 mm. Conclusion. Extracorporeal perfusion of bovine livers with consecutive standardized RF

  11. Ablator Response Model Development: From Flight Data Back to Fundamental Experiments

    NASA Technical Reports Server (NTRS)

    Mansour, Nagi N.; Lachaud, Jean R.

    2013-01-01

    The successful Mars atmospheric entry by the Mars Science Laboratory (MSL-Curiosity) combined with the success of the Earth atmospheric entry by the Stardust capsule have established PICA as a major Thermal Protection Systems (TPS) material. We expect that this class of materials will be on the short list selected by NASA for any atmospheric entry missions and that it will be the lead of that list of materials in any planning, feasibility studies or flight readiness studies. In addition to NASAs successes, the Dragon capsule, the successful commercial space vehicle built by SpaceX, uses PICA-X, while the European Space Agency is considering ASTERM for its exploration missions that involve atmospheric entries, both of these materials are of the same family as PICA. In the talk, a high-fidelity model will be detailed and discussed. The model tracks the chemical composition of the gases produced during pyrolysis. As in the conventional models, it uses equilibrium chemistry to determine the recession rate at high temperatures but switches to in-volume finite-rate ablation for lower temperatures. It also tracks the time evolution of the porosity of the material. Progress in implementing this high-fidelity model in a code will be presented. In addition, a set of basic experimental data being supported for model validation will be summarized. The validation process for the model development will be discussed. Preliminary results will be presented for a case where detailed pyrolysis product chemistry is computed. Finally, a wish list for a set of validation experiments will be outlined and discussed.

  12. Exogenous chromophores in Nd:YAG laser selective ablation of the model tissue

    NASA Astrophysics Data System (ADS)

    Vinduska, Vladimir

    1993-06-01

    Exogenous chromophores have the capability to enhance atheromatous plaque ablation during laser angioplasty. A number of dyes have been tested for their effect on the tissue absorption for lasers emitting at different wavelengths, but little is known about conditions governing this selectivity. 1064 nm and 1300 nm light transmission and scattering of 0.6 mm thick samples of agar with different concentrations of talc and black ink were compared to those of atheromatous tissue of the same thickness in order to determine the sample with most similar optical properties. We measured ablation threshold in air for both wavelengths, temperatures in adjacent agar in air for both wavelengths, ablation thresholds in water for 1064 nm, temperatures in the adjacent agar in the water for 1064 nm, ablation threshold in the air for 1064 nm and 5, 10, and 15 mm fiber tip distances. Selectivity of the laser ablation is achievable by saturation of the tissue with chromophore dyes. Higher absorption results in lower thermal damage of non-ablated tissue, especially in water. Selectivity in water is more pronounced than that in air. Selectivity was not influenced by the size of the laser spot in the investigated range.

  13. Validation of accuracy of liver model with temperature-dependent thermal conductivity by comparing the simulation and in vitro RF ablation experiment.

    PubMed

    Watanabe, Hiroki; Yamazaki, Nozomu; Isobe, Yosuke; Lu, XiaoWei; Kobayashi, Yo; Miyashita, Tomoyuki; Ohdaira, Takeshi; Hashizume, Makoto; Fujie, Masakatsu G

    2012-01-01

    Radiofrequency (RF) ablation is increasingly used to treat cancer because it is minimally invasive. However, it is difficult for operators to control precisely the formation of coagulation zones because of the inadequacies of imaging modalities. To overcome this limitation, we previously proposed a model-based robotic ablation system that can create the required size and shape of coagulation zone based on the dimensions of the tumor. At the heart of such a robotic system is a precise temperature distribution simulator for RF ablation. In this article, we evaluated the simulation accuracy of two numerical simulation liver models, one using a constant thermal conductivity value and the other using temperature-dependent thermal conductivity values, compared with temperatures obtained using in vitro experiments. The liver model that reflected the temperature dependence of thermal conductivity did not result in a large increase of simulation accuracy compared with the temperature-independent model in the temperature range achieved during clinical RF ablation.

  14. Theoretical modeling of laser ablation of quaternary bronze alloys: case studies comparing femtosecond and nanosecond LIBS experimental data.

    PubMed

    Fornarini, Lucilla; Fantoni, Roberta; Colao, Francesco; Santagata, Antonio; Teghil, Roberto; Elhassan, Asmaa; Harith, Mohamed A

    2009-12-31

    A model, formerly proposed and utilized to understand the formation of laser induced breakdown spectroscopy (LIBS) plasma upon irradiation with nanosecond laser pulses at different fluences and wavelengths, has been extended to the irradiation with femtosecond laser pulses in order to control the fractionation mechanisms which heavily affect the application of laser-ablation-based microanalytical techniques. The model takes into account the different chemico-physical processes occurring during the interaction of an ultrashort laser pulse with a metallic surface. In particular, a two-temperature description, relevant to the electrons and lattice of the substrate, respectively, has been introduced and applied to different ternary and quaternary copper-based alloys subjected to fs and ns ablation both in the visible (527 nm) and in the UV (248 nm). The model has been found able to reproduce the shorter plasma duration experimentally found upon fs laser ablation. Kinetic decay times of several copper (major element) emission lines have been examined together with those relevant to the main plasma parameters. The plasma experimental temperature, derived assuming a Boltzmann distribution, and the electron density following the Saha equation have been compared with the corresponding theoretical data. A satisfactory description of plasma parameters and main matrix constituent composition has been obtained in the time window where local thermal equilibrium was assumed for LIBS data analysis. Improved analytical capabilities are predicted upon delayed detection of plasma emission in femtosecond LIBS, in relation to the better LOD achieved and to the improved data reproducibility expected. Results support the utilization of ultrafast laser sources for trace detection, despite the residual fractionation occurring in the examined range of fluences which affects the linearity of experimental calibration curves built for tin and lead after internal standardization on copper. The

  15. Optical-thermal mathematical model for endovenous laser ablation of varicose veins.

    PubMed

    van Ruijven, Peter W M; Poluektova, Anna A; van Gemert, Martin J C; Neumann, H A Martino; Nijsten, Tamar; van der Geld, Cees W M

    2014-03-01

    Endovenous laser ablation (EVLA) is successfully used to treat varicose veins. However, the exact working mechanism is still not fully identified and the clinical procedure is not yet standardized. Mathematical modeling of EVLA could strongly improve our understanding of the influence of the various EVLA processes. The aim of this study is to combine Mordon's optical-thermal model with the presence of a strongly absorbing carbonized blood layer on the fiber tip. The model anatomy includes a cylindrically symmetric blood vessel surrounded by an infinite homogenous perivenous tissue. The optical fiber is located in the center of the vessel and is withdrawn with a pullback velocity. The fiber tip includes a small layer of strongly absorbing material, representing the layer of carbonized blood, which absorbs 45% of the emitted laser power. Heat transfer due to boiling bubbles is taken into account by increasing the heat conduction coefficient by a factor of 200 for temperatures above 95 °C. The temperature distribution in the blood, vessel wall, and surrounding medium is calculated from a numerical solution of the bioheat equation. The simulations were performed in MATLAB™ and validated with the aid of an analytical solution. The simulations showed, first, that laser wavelength did virtually not influence the simulated temperature profiles in blood and vessel wall, and, second, that temperatures of the carbonized blood layer varied slightly, from 952 to 1,104 °C. Our improved mathematical optical-thermal EVLA model confirmed previous predictions and experimental outcomes that laser wavelength is not an important EVLA parameter and that the fiber tip reaches exceedingly high temperatures.

  16. A multiphase model for pulsed ns-laser ablation of copper in an ambient gas

    SciTech Connect

    Autrique, D.; Chen, Z.; Alexiades, V.; Bogaerts, A.; Rethfeld, B.

    2012-07-30

    Laser ablation in an ambient gas is nowadays used in a growing number of applications, such as chemical analysis and pulsed laser deposition. Despite the many applications, the technique is still poorly understood. Therefore models describing the material evolution in time during short pulse laser irradiation can be helpful to unravel the puzzle and finally result in the optimization of the related applications. In the present work, a copper target is immersed in helium, initially set at atmospheric pressure and room temperature. Calculations are performed for a Gaussian-shaped laser pulse with a wavelength of 532 nm, full width at half maximum of 6 ns, and laser fluences up to 10 J/cm{sup 2}. In order to describe the transient behaviour in and above the copper target, hydrodynamic equations are solved. An internal energy method accounting for pressure relaxation is applied for the description of the target. In the plume domain a set of conservation equations is solved, assuming local thermodynamic equilibrium. Calculated crater depths and transmission profiles are compared with experimental results and similar trends are found. Our calculations indicate that for the laser fluence regime under study, explosive boiling could play a fundamental role in the plasma formation of metals under ns-pulsed laser irradiation.

  17. The Importance of Ablation on ice Flow and Meteorite Exhumation: the Physical Modeling Approach at Frontier Mountain, Antarctica

    NASA Astrophysics Data System (ADS)

    Zeoli, A.; Folco, L.; Corti, G.

    2008-12-01

    The highest concentration of meteorites yet discovered on Earth is found in the ice sheet covering Antarctica. Major meteorite accumulation zones often occur in front of submerged or emerged bedrock obstacles, where the meteorite-bearing ice slows down, is uplifted by the buttressing effect and exhumed and concentrated by wind ablation ("ice-flow model"). Meteorite traps have also been discovered in the downstream side of major emerged bedrock barriers, as in the Frontier Mountain (FM) region, a nunatak outcropping in the Northern Victoria Land, Antarctica, 250 km from the Italian Terra Nova Base. However, recent detailed glaciological analyses indicate that also for this site the "ice-flow model" remains the best concentration explanation, being present an important submerged barrier in the main blue-ice field. A this site, during the last fifteen years, more than 1000 meteorites have been there collected. During the various field expeditions, different data were acquired to allow a detailed study of the local glaciodynamics. This large data set was used to constrain boundary conditions for performing a set of physical experiments reproducing the main glaciodynamics characteristics of the FM region. In addition to previous result, now we performed a series of experiments that consider also the ablation effect in order to better reproduce the natural environment. Analog experiments were performed at the Tectonic Modelling Laboratory of the CNR-IGG (Florence, Italy). Polydimethilsyloxane (PDMS) is used to simulate glacial flow in analog models; this material properly simulates the rheological behaviour of ice (Corti et al, 2003; Corti et al, 2008). Models are built inside a Plexiglas box with dimensions of 70cm x 20cm x 10cm. The models are scaled to nature conditions allowing a comparison between laboratories and natural models. The geometrical scaling ratio was of 2*10-5, such that 1 cm in the model represented about 500 m in nature. In order to measure the

  18. 1-D Transient Thermal Modeling of an Ablative Material (MCC-1) Exposed to a Simulated Convective Titan 4 Launch Environment

    NASA Technical Reports Server (NTRS)

    Reinarts, Thomas R.; Crain, William K.; Stuckey, C. Irvin; Palko, Richard L.

    1998-01-01

    The purpose of the work is to demonstrate that the flat test panel substrate temperatures are consistent with analysis predictions for MCC-1 applied to a aluminum substrate. The testing was performed in an aerothermal facility on samples of three different thicknesses of MCC-1 on an aluminum substrate. The results of the test were compared with a Transient Thermal model. The key assumptions of the Transient Thermal model were: (1) a one-dimensional heat transfer; (2) a constant ablation recession rate (determined from pre and post-test measurements); (3) ablation temperature of 540 degrees F; (4) Char left behind the ablation front; and (5) temperature jump correction for incident heat transfer coefficient. Two methods were used to model the heating of bare MCC-1: (1) Directly input surface temperature as a function of time; and (2) Aerothermal heating using calibration plate data and subtracting the radiation losses to tunnel walls. The results are presented as graphs. This article is presented in Viewgraph format.

  19. Characterization of tissue response to radiofrequency ablation using 3D model-based analysis of interventional MR images

    NASA Astrophysics Data System (ADS)

    Weinberg, Brent D.; Lazebnik, Roee S.; Breen, Michael S.; Lewin, Jonathan S.; Wilson, David L.

    2003-05-01

    Using magnetic resonance imaging (MRI), real-time guidance is feasible for radiofrequency (RF) current ablation of pathologic tissue. Lesions have a characteristic two-zone appearance: an inner core (Zone I) surrounded by a hyper-intense rim (Zone II). A better understanding of both the immediate (hyper-acute) and delayed (sub-acute) physiological response of the target tissue will aid development of minimally invasive tumor treatment strategies. We performed in vivo RF ablations in a rabbit thigh model and characterized the tissue response to treatment through contrast enhanced (CE) T1 and T2 weighted MR images at two time points. We measured zonal grayscale changes as well as zone volume changes using a 3D computationally fitted globally deformable parametric model. Comparison over time demonstrated an increase in the volume of both the inner necrotic core (mean 56.5% increase) and outer rim (mean 16.8% increase) of the lesion. Additionally, T2 images of the lesion exhibited contrast greater than or equal to CE T1 (mean 35% improvement). This work establishes a foundation for the clinical use of T2 MR images coupled with a geometric model of the ablation for noninvasive lesion monitoring and characterization.

  20. Dynamic T2-mapping during magnetic resonance guided high intensity focused ultrasound ablation of bone marrow

    NASA Astrophysics Data System (ADS)

    Waspe, Adam C.; Looi, Thomas; Mougenot, Charles; Amaral, Joao; Temple, Michael; Sivaloganathan, Siv; Drake, James M.

    2012-11-01

    Focal bone tumor treatments include amputation, limb-sparing surgical excision with bone reconstruction, and high-dose external-beam radiation therapy. Magnetic resonance guided high intensity focused ultrasound (MR-HIFU) is an effective non-invasive thermotherapy for palliative management of bone metastases pain. MR thermometry (MRT) measures the proton resonance frequency shift (PRFS) of water molecules and produces accurate (<1°C) and dynamic (<5s) thermal maps in soft tissues. PRFS-MRT is ineffective in fatty tissues such as yellow bone marrow and, since accurate temperature measurements are required in the bone to ensure adequate thermal dose, MR-HIFU is not indicated for primary bone tumor treatments. Magnetic relaxation times are sensitive to lipid temperature and we hypothesize that bone marrow temperature can be determined accurately by measuring changes in T2, since T2 increases linearly in fat during heating. T2-mapping using dual echo times during a dynamic turbo spin-echo pulse sequence enabled rapid measurement of T2. Calibration of T2-based thermal maps involved heating the marrow in a bovine femur and simultaneously measuring T2 and temperature with a thermocouple. A positive T2 temperature dependence in bone marrow of 20 ms/°C was observed. Dynamic T2-mapping should enable accurate temperature monitoring during MR-HIFU treatment of bone marrow and shows promise for improving the safety and reducing the invasiveness of pediatric bone tumor treatments.

  1. Model-based feasibility assessment and evaluation of prostate hyperthermia with a commercial MR-guided endorectal HIFU ablation array

    SciTech Connect

    Salgaonkar, Vasant A. Hsu, I-C.; Diederich, Chris J.; Prakash, Punit; Rieke, Viola; Ozhinsky, Eugene; Kurhanewicz, John; Plata, Juan

    2014-03-15

    Purpose: Feasibility of targeted and volumetric hyperthermia (40–45 °C) delivery to the prostate with a commercial MR-guided endorectal ultrasound phased array system, designed specifically for thermal ablation and approved for ablation trials (ExAblate 2100, Insightec Ltd.), was assessed through computer simulations and tissue-equivalent phantom experiments with the intention of fast clinical translation for targeted hyperthermia in conjunction with radiotherapy and chemotherapy. Methods: The simulations included a 3D finite element method based biothermal model, and acoustic field calculations for the ExAblate ERUS phased array (2.3 MHz, 2.3 × 4.0 cm{sup 2}, ∼1000 channels) using the rectangular radiator method. Array beamforming strategies were investigated to deliver protracted, continuous-wave hyperthermia to focal prostate cancer targets identified from representative patient cases. Constraints on power densities, sonication durations and switching speeds imposed by ExAblate hardware and software were incorporated in the models. Preliminary experiments included beamformed sonications in tissue mimicking phantoms under MR temperature monitoring at 3 T (GE Discovery MR750W). Results: Acoustic intensities considered during simulation were limited to ensure mild hyperthermia (T{sub max} < 45 °C) and fail-safe operation of the ExAblate array (spatial and time averaged acoustic intensity I{sub SATA} < 3.4 W/cm{sup 2}). Tissue volumes with therapeutic temperature levels (T > 41 °C) were estimated. Numerical simulations indicated that T > 41 °C was calculated in 13–23 cm{sup 3} volumes for sonications with planar or diverging beam patterns at 0.9–1.2 W/cm{sup 2}, in 4.5–5.8 cm{sup 3} volumes for simultaneous multipoint focus beam patterns at ∼0.7 W/cm{sup 2}, and in ∼6.0 cm{sup 3} for curvilinear (cylindrical) beam patterns at 0.75 W/cm{sup 2}. Focused heating patterns may be practical for treating focal disease in a single posterior

  2. Approaches for modeling interstitial ultrasound ablation of tumors within or adjacent to bone: Theoretical and experimental evaluations

    PubMed Central

    Scott, Serena J.; Prakash, Punit; Salgaonkar, Vasant; Jones, Peter D.; Cam, Richard N.; Han, Misung; Rieke, Viola; Burdette, E. Clif; Diederich, Chris J.

    2014-01-01

    Purpose The objectives of this study were to develop numerical models of interstitial ultrasound ablation of tumors within or adjacent to bone, to evaluate model performance through theoretical analysis, and to validate the models and approximations used through comparison to experiments. Methods 3D transient biothermal and acoustic finite element models were developed, employing four approximations of 7 MHz ultrasound propagation at bone/soft tissue interfaces. The various approximations considered or excluded reflection, refraction, angle-dependence of transmission coefficients, shear mode conversion, and volumetric heat deposition. Simulations were performed for parametric and comparative studies. Experiments within ex vivo tissues and phantoms were performed to validate the models by comparison to simulations. Temperature measurements were conducted using needle thermocouples or MR temperature imaging (MRTI). Finite element models representing heterogeneous tissue geometries were created based on segmented MR images. Results High ultrasound absorption at bone/soft tissue interfaces increased the volumes of target tissue that could be ablated. Models using simplified approximations produced temperature profiles closely matching both more comprehensive models and experimental results, with good agreement between 3D calculations and MRTI. The correlation coefficients between simulated and measured temperature profiles in phantoms ranged from 0.852 to 0.967 (p-value < 0.01) for the four models. Conclusions Models using approximations of interstitial ultrasound energy deposition around bone/soft tissue interfaces produced temperature distributions in close agreement with comprehensive simulations and experimental measurements. These models may be applied to accurately predict temperatures produced by interstitial ultrasound ablation of tumors near and within bone, with applications toward treatment planning. PMID:24102393

  3. The Feasibility of HIFU Liver Ablation Through the Ribcage and Cartilage in a Rodent Model

    NASA Astrophysics Data System (ADS)

    King, Randy; Rieke, Viola; Pauly, Kim Butts

    2009-04-01

    We examined the feasibility of the rat model for the study of HIFU treatment of liver cancer. Significance: HIFU is being developed for the minimally invasive treatment of primary and metastatic liver cancer. In patients, obstruction of the ultrasound by the ribs poses a significant problem, and current studies are under way which investigate the efficacy of focusing around or sonicating between the ribs. Such techniques show promise for patient treatments, but are not feasible when using rodent models. Results: Six recently euthanized (within the hour) Sprague-Dewey rats were used. The hair over the anterior surface was removed. Sonications were performed with the InSightec ExAblate system at 0.95 MHz, 1.1 MHz, and 1.35MHz through the rib cage. Temperature rise was monitored with MRI-based thermometry. Lesions were created in the livers of 5/6 rats. In the five rats, energy levels between 572-1194 Joules produced lesions every time. With energies greater than 1393 Joules, skin damaged was observed which prevented the ultrasound from propagating to the liver on subsequent sonications, accounting for the one study that failed to produce lesions. No thermal damage was observed at the skin with sonications that resulted in liver lesions, and no significant heating was observed at or near the skin in the MRI temperature maps. Conclusions: It is possible to ignore the effect of ribs and sternum in rodents and create lesions within the rat liver. This technique opens the door to using hepatocellular carcinoma rodent models in HIFU studies.

  4. Launch Vehicle Dynamics Demonstrator Model

    NASA Technical Reports Server (NTRS)

    1963-01-01

    Launch Vehicle Dynamics Demonstrator Model. The effect of vibration on launch vehicle dynamics was studied. Conditions included three modes of instability. The film includes close up views of the simulator fuel tank with and without stability control. [Entire movie available on DVD from CASI as Doc ID 20070030984. Contact help@sti.nasa.gov

  5. Ultrasound ablation enhances drug accumulation and survival in mammary carcinoma models

    PubMed Central

    Wong, Andrew W.; Fite, Brett Z.; Liu, Yu; Kheirolomoom, Azadeh; Seo, Jai W.; Watson, Katherine D.; Mahakian, Lisa M.; Tam, Sarah M.; Zhang, Hua; Foiret, Josquin; Borowsky, Alexander D.; Ferrara, Katherine W.

    2015-01-01

    Magnetic resonance–guided focused ultrasound (MRgFUS) facilitates noninvasive image-guided conformal thermal therapy of cancer. Yet in many scenarios, the sensitive tissues surrounding the tumor constrain the margins of ablation; therefore, augmentation of MRgFUS with chemotherapy may be required to destroy remaining tumor. Here, we used 64Cu-PET-CT, MRI, autoradiography, and fluorescence imaging to track the kinetics of long-circulating liposomes in immunocompetent mammary carcinoma–bearing FVB/n and BALB/c mice. We observed a 5-fold and 50-fold enhancement of liposome and drug concentration, respectively, within MRgFUS thermal ablation–treated tumors along with dense accumulation within the surrounding tissue rim. Ultrasound-enhanced drug accumulation was rapid and durable and greatly increased total tumor drug exposure over time. In addition, we found that the small molecule gadoteridol accumulates around and within ablated tissue. We further demonstrated that dilated vasculature, loss of vascular integrity resulting in extravasation of blood cells, stromal inflammation, and loss of cell-cell adhesion and tissue architecture all contribute to the enhanced accumulation of the liposomes and small molecule probe. The locally enhanced liposome accumulation was preserved even after a multiweek protocol of doxorubicin-loaded liposomes and partial ablation. Finally, by supplementing ablation with concurrent liposomal drug therapy, a complete and durable response was obtained using protocols for which a sub-mm rim of tumor remained after ablation. PMID:26595815

  6. Laser ablation of concrete.

    SciTech Connect

    Savina, M.

    1998-10-05

    Laser ablation is effective both as an analytical tool and as a means of removing surface coatings. The elemental composition of surfaces can be determined by either mass spectrometry or atomic emission spectroscopy of the atomized effluent. Paint can be removed from aircraft without damage to the underlying aluminum substrate, and environmentally damaged buildings and sculptures can be restored by ablating away deposited grime. A recent application of laser ablation is the removal of radioactive contaminants from the surface and near-surface regions of concrete. We present the results of ablation tests on concrete samples using a high power pulsed Nd:YAG laser with fiber optic beam delivery. The laser-surface interaction was studied on various model systems consisting of Type I Portland cement with varying amounts of either fine silica or sand in an effort to understand the effect of substrate composition on ablation rates and mechanisms. A sample of non-contaminated concrete from a nuclear power plant was also studied. In addition, cement and concrete samples were doped with non-radioactive isotopes of elements representative of cooling waterspills, such as cesium and strontium, and analyzed by laser-resorption mass spectrometry to determine the contamination pathways. These samples were also ablated at high power to determine the efficiency with which surface contaminants are removed and captured. The results show that the neat cement matrix melts and vaporizes when little or no sand or aggregate is present. Surface flows of liquid material are readily apparent on the ablated surface and the captured aerosol takes the form of glassy beads up to a few tens of microns in diameter. The presence of sand and aggregate particles causes the material to disaggregate on ablation, with intact particles on the millimeter size scale leaving the surface. Laser resorption mass spectrometric analysis showed that cesium and potassium have similar chemical environments in the

  7. Emission features and expansion dynamics of nanosecond laser ablation plumes at different ambient pressures

    SciTech Connect

    Farid, N.; Harilal, S. S. Hassanein, A.; Ding, H.

    2014-01-21

    The influence of ambient pressure on the spectral emission features and expansion dynamics of a plasma plume generated on a metal target has been investigated. The plasma plumes were generated by irradiating Cu targets using 6 ns, 1064 nm pulses from a Q-switched Nd:YAG laser. The emission and expansion dynamics of the plasma plumes were studied by varying air ambient pressure levels ranging from vacuum to atmospheric pressure. The ambient pressure levels were found to affect both the line intensities and broadening along with the signal to background and signal to noise ratios and the optimum pressure conditions for analytical applications were evaluated. The characteristic plume parameters were estimated using emission spectroscopy means and noticed that the excitation temperature peaked ∼300 Torr, while the electron density showed a maximum ∼100 Torr. Fast-gated images showed a complex interaction between the plume and background air leading to changes in the plume geometry with pressure as well as time. Surface morphology of irradiated surface showed that the pressure of the ambient gas affects the laser-target coupling significantly.

  8. A unified model to determine the energy partitioning between target and plasma in nanosecond laser ablation of silicon

    SciTech Connect

    Galasso, G.; Kaltenbacher, M.; Tomaselli, A.; Scarpa, D.

    2015-03-28

    In semiconductor industry, pulsed nanosecond lasers are widely applied for the separation of silicon wafers. Here, the high intensities employed activate a cascade of complex multi-physical and multi-phase mechanisms, which finally result in the formation of a laser induced plasma, shielding the target from the incoming laser beam. Such induced plasma plume, by preventing the laser to effectively reach the target, reduces the overall efficiency and controllability of the ablation process. Modelling can be a useful tool in the optimization of industrial laser applications, allowing a deeper understanding of the way the laser energy distributes between target and induced plasma. Nevertheless, the highly multi-physical character of laser ablation poses serious challenges on the implementation of the various mechanisms underlying the process within a common modelling framework. A novel strategy is here proposed in order to simulate in a simplified, yet physically consistent way, a typical industrial application as laser ablation of silicon wafers. Reasonable agreement with experimental findings is obtained. Three fundamental mechanisms have been identified as the main factors influencing the accuracy of the numerical predictions: the transition from evaporative to volumetric mass removal occurring at critical temperature, the collisional and radiative processes underlying the initial plasma formation stage and the increased impact of the liquid ejection mechanism when a sub-millimeter laser footprint is used.

  9. SSME structural dynamic model development

    NASA Technical Reports Server (NTRS)

    Foley, M. J.; Tilley, D. M.; Welch, C. T.

    1983-01-01

    A mathematical model of the Space Shuttle Main Engine (SSME) as a complete assembly, with detailed emphasis on LOX and High Fuel Turbopumps is developed. The advantages of both complete engine dynamics, and high fidelity modeling are incorporated. Development of this model, some results, and projected applications are discussed.

  10. Histotripsy Focal Ablation of Implanted Prostate Tumor in an ACE-1 Canine Cancer Model

    PubMed Central

    Schade, George R.; Keller, Jill; Ives, Kim; Cheng, Xu; Rosol, Thomas J.; Keller, Evan; Roberts, William W.

    2015-01-01

    Purpose Histotripsy is a nonthermal ablative focused ultrasound technology with possible future applications for prostate cancer focal therapy. We used the ACE-1 prostate tumor model and evaluated the feasibility of treating prostate tumors with histotripsy. Materials and Methods A total of 10 immunosuppressed (cyclosporine treated) canine subjects received transrectal ultrasound guided percutaneous intraprostatic injection of ACE-1 canine prostate cancer cells. Prostates were serially imaged with transrectal ultrasound to monitor tumor growth. Subjects were sham treated (3) or underwent transabdominal histotripsy of the prostate, which targeted implanted tumor and adjacent parenchyma using a 750 kHz piezoelectric ultrasound therapy transducer. Prostates were examined histologically to confirm tumor and the histotripsy treatment effect. Results ACE-1 tumors were visualized on transrectal ultrasound in all 10 subjects within 2 weeks of tumor injection. Lesions demonstrated growth in the prostatic capsule, glandular lobules, fibrous septa and periurethral stroma with significant desmoplastic reaction and areas of central necrosis on histology. Lymph node and/or pulmonary metastases developed in 4 subjects. Ultrasound tumor localization and initiation of cavitation during histotripsy therapy were feasible in all treated subjects. Histologically there was evidence of homogenization of tumor and prostatic parenchyma in all 4 acute subjects with necrosis and hemorrhage in the 3 chronic subjects. Conclusions This study shows the feasibility of histotripsy destruction of prostate tumors in a canine ACE-1 model. It suggests a potential role for histotripsy based focal therapy for prostate cancer. Further studies are needed to better characterize the effects of histotripsy on malignant tissues. PMID:22999534

  11. COLD-SAT dynamic model

    NASA Technical Reports Server (NTRS)

    Adams, Neil S.; Bollenbacher, Gary

    1992-01-01

    This report discusses the development and underlying mathematics of a rigid-body computer model of a proposed cryogenic on-orbit liquid depot storage, acquisition, and transfer spacecraft (COLD-SAT). This model, referred to in this report as the COLD-SAT dynamic model, consists of both a trajectory model and an attitudinal model. All disturbance forces and torques expected to be significant for the actual COLD-SAT spacecraft are modeled to the required degree of accuracy. Control and experimental thrusters are modeled, as well as fluid slosh. The model also computes microgravity disturbance accelerations at any specified point in the spacecraft. The model was developed by using the Boeing EASY5 dynamic analysis package and will run on Apollo, Cray, and other computing platforms.

  12. Dynamic Modeling of ALS Systems

    NASA Technical Reports Server (NTRS)

    Jones, Harry

    2002-01-01

    The purpose of dynamic modeling and simulation of Advanced Life Support (ALS) systems is to help design them. Static steady state systems analysis provides basic information and is necessary to guide dynamic modeling, but static analysis is not sufficient to design and compare systems. ALS systems must respond to external input variations and internal off-nominal behavior. Buffer sizing, resupply scheduling, failure response, and control system design are aspects of dynamic system design. We develop two dynamic mass flow models and use them in simulations to evaluate systems issues, optimize designs, and make system design trades. One model is of nitrogen leakage in the space station, the other is of a waste processor failure in a regenerative life support system. Most systems analyses are concerned with optimizing the cost/benefit of a system at its nominal steady-state operating point. ALS analysis must go beyond the static steady state to include dynamic system design. All life support systems exhibit behavior that varies over time. ALS systems must respond to equipment operating cycles, repair schedules, and occasional off-nominal behavior or malfunctions. Biological components, such as bioreactors, composters, and food plant growth chambers, usually have operating cycles or other complex time behavior. Buffer sizes, material stocks, and resupply rates determine dynamic system behavior and directly affect system mass and cost. Dynamic simulation is needed to avoid the extremes of costly over-design of buffers and material reserves or system failure due to insufficient buffers and lack of stored material.

  13. Aircraft Dynamic Modeling in Turbulence

    NASA Technical Reports Server (NTRS)

    Morelli, Eugene A.; Cunninham, Kevin

    2012-01-01

    A method for accurately identifying aircraft dynamic models in turbulence was developed and demonstrated. The method uses orthogonal optimized multisine excitation inputs and an analytic method for enhancing signal-to-noise ratio for dynamic modeling in turbulence. A turbulence metric was developed to accurately characterize the turbulence level using flight measurements. The modeling technique was demonstrated in simulation, then applied to a subscale twin-engine jet transport aircraft in flight. Comparisons of modeling results obtained in turbulent air to results obtained in smooth air were used to demonstrate the effectiveness of the approach.

  14. Model describes subsea control dynamics

    SciTech Connect

    Not Available

    1988-02-01

    A mathematical model of the hydraulic control systems for subsea completions and their umbilicals has been developed and applied successfully to Jabiru and Challis field production projects in the Timor Sea. The model overcomes the limitations of conventional linear steady state models and yields for the hydraulic system an accurate description of its dynamic response, including the valve shut-in times and the pressure transients. Results of numerical simulations based on the model are in good agreement with measurements of the dynamic response of the tree valves and umbilicals made during land testing.

  15. Quantitative modeling of the accuracy in registering preoperative patient-specific anatomic models into left atrial cardiac ablation procedures

    SciTech Connect

    Rettmann, Maryam E. Holmes, David R.; Camp, Jon J.; Cameron, Bruce M.; Robb, Richard A.; Kwartowitz, David M.; Gunawan, Mia; Johnson, Susan B.; Packer, Douglas L.; Dalegrave, Charles; Kolasa, Mark W.

    2014-02-15

    Purpose: In cardiac ablation therapy, accurate anatomic guidance is necessary to create effective tissue lesions for elimination of left atrial fibrillation. While fluoroscopy, ultrasound, and electroanatomic maps are important guidance tools, they lack information regarding detailed patient anatomy which can be obtained from high resolution imaging techniques. For this reason, there has been significant effort in incorporating detailed, patient-specific models generated from preoperative imaging datasets into the procedure. Both clinical and animal studies have investigated registration and targeting accuracy when using preoperative models; however, the effect of various error sources on registration accuracy has not been quantitatively evaluated. Methods: Data from phantom, canine, and patient studies are used to model and evaluate registration accuracy. In the phantom studies, data are collected using a magnetically tracked catheter on a static phantom model. Monte Carlo simulation studies were run to evaluate both baseline errors as well as the effect of different sources of error that would be present in a dynamicin vivo setting. Error is simulated by varying the variance parameters on the landmark fiducial, physical target, and surface point locations in the phantom simulation studies. In vivo validation studies were undertaken in six canines in which metal clips were placed in the left atrium to serve as ground truth points. A small clinical evaluation was completed in three patients. Landmark-based and combined landmark and surface-based registration algorithms were evaluated in all studies. In the phantom and canine studies, both target registration error and point-to-surface error are used to assess accuracy. In the patient studies, no ground truth is available and registration accuracy is quantified using point-to-surface error only. Results: The phantom simulation studies demonstrated that combined landmark and surface-based registration improved

  16. A method for deriving the coagulation boundary of liver tissue using a relational model of viscoelasticity and temperature in radio frequency ablation.

    PubMed

    Lu, Xiaowei; Tsukune, Mariko; Watanabe, Hiroki; Yamazaki, Nozomu; Isobe, Yosuke; Kobayashi, Yo; Miyashita, Tomoyuki; Fujie, Masakatsu G

    2012-01-01

    Recently radiofrequency (RF) ablation has become increasingly important in treating liver cancers. RF ablation is ordinarily conducted using elastographic imaging to monitor the ablation procedure and the temperature of the electrode needle is displayed on the RF generator. However, the coagulation boundary of liver tissue in RF ablation is unclear and unconfident. This can lead to both excessive and insufficient RF ablation thereby diminishing the advantages of the procedure. In the present study, we developed a method for determining the coagulation boundary of liver tissue in RF ablation. To investigate this boundary we used the mechanical characteristics of biochemical components as an indicator of coagulation to produce a relational model for viscoelasticity and temperature. This paper presents the data acquisition procedures for the viscoelasticity characteristics and the analytical method used for the coagulation model. We employed a rheometer to measure the viscoelastic characteristics of liver tissue. To determine the model functional relationship between viscoelasticity and temperature, we used a least-square method and the minimum root mean square error was calculated to optimize the model functional relations. The functional relation between temperature and viscoelasticity was linear and non-linear in different temperature regions. The boundary between linear and non-linear functional relation was 58.0°C. PMID:23365863

  17. Dynamic Eye Model.

    ERIC Educational Resources Information Center

    Journal of Science and Mathematics Education in Southeast Asia, 1981

    1981-01-01

    Instructions (with diagrams and parts list) are provided for constructing an eye model with a pliable lens made from a plastic bottle which can vary its convexity to accommodate changing positions of an object being viewed. Also discusses concepts which the model can assist in developing. (Author/SK)

  18. Ablating adult neurogenesis in the rat has no effect on spatial processing: evidence from a novel pharmacogenetic model.

    PubMed

    Groves, James O; Leslie, Isla; Huang, Guo-Jen; McHugh, Stephen B; Taylor, Amy; Mott, Richard; Munafò, Marcus; Bannerman, David M; Flint, Jonathan

    2013-01-01

    The function of adult neurogenesis in the rodent brain remains unclear. Ablation of adult born neurons has yielded conflicting results about emotional and cognitive impairments. One hypothesis is that adult neurogenesis in the hippocampus enables spatial pattern separation, allowing animals to distinguish between similar stimuli. We investigated whether spatial pattern separation and other putative hippocampal functions of adult neurogenesis were altered in a novel genetic model of neurogenesis ablation in the rat. In rats engineered to express thymidine kinase (TK) from a promoter of the rat glial fibrillary acidic protein (GFAP), ganciclovir treatment reduced new neurons by 98%. GFAP-TK rats showed no significant difference from controls in spatial pattern separation on the radial maze, spatial learning in the water maze, contextual or cued fear conditioning. Meta-analysis of all published studies found no significant effects for ablation of adult neurogenesis on spatial memory, cue conditioning or ethological measures of anxiety. An effect on contextual freezing was significant at a threshold of 5% (P = 0.04), but not at a threshold corrected for multiple testing. The meta-analysis revealed remarkably high levels of heterogeneity among studies of hippocampal function. The source of this heterogeneity remains unclear and poses a challenge for studies of the function of adult neurogenesis. PMID:24039591

  19. Local delivery of a selective androgen receptor modulator failed as an anabolic agent in a rat bone marrow ablation model

    PubMed Central

    Aro, Hannu T; Kulkova, Julia; Moritz, Niko; Kähkönen, Esa; Mattila, Riina H

    2015-01-01

    Background and purpose — Selective androgen receptor modulators (SARMs) have been developed to have systemic anabolic effects on bones and muscles without the adverse effects of steroidal androgens. One unexplored therapeutic option is the targeted application of SARMs for the enhancement of local new bone formation. We evaluated the osteogenic efficacy of a locally released SARM (ORM-11984). Methods — ORM-11984 was mixed with a copolymer of L-lactide and ɛ-caprolactone (PLCL). An in vitro dissolution test confirmed the sustainable release of ORM-11984 from the matrix. A bone marrow ablation model was used in female Sprague-Dawley rats. Implants containing 10%, 30%, or 50% ORM-11984 by weight or pure PLCL were inserted into the medullary canal of the ablated tibia. At 6 and 12 weeks, the volume of intramedullary new bone and the perimeter of bone-implant contact were measured by micro-computed tomography and histomorphometry. Results — Contrary to our hypothesis, there was a negative correlation between the amount of new bone around the implant and the dose of ORM-11984. There was only a mild (and not statistically significant) enhancement of bone formation in ablated bones subjected to the lowest dose of the SARM (10%). Interpretation — This study suggests that intramedullary/endosteal osteogenesis had a negative, dose-dependent response to locally released SARM. This result highlights the complexity of androgenic effects on bones and also suggests that there are biological limits to the targeted local application of SARMs. PMID:26198725

  20. Genetic Ablation of Parietal Cells in Transgenic Mice: A New Model for Analyzing Cell Lineage Relationships in the Gastric Mucosa

    NASA Astrophysics Data System (ADS)

    Canfield, Victor; West, A. Brian; Goldenring, James R.; Levenson, Robert

    1996-03-01

    The gastric mucosa of mammalian stomach contains several differentiated cell types specialized for the secretion of acid, digestive enzymes, mucus, and hormones. Understanding whether each of these cell lineages is derived from a common stem cell has been a challenging problem. We have used a genetic approach to analyze the ontogeny of progenitor cells within mouse stomach. Herpes simplex virus 1 thymidine kinase was targeted to parietal cells within the gastric mucosa of transgenic mice, and parietal cells were ablated by treatment of animals with the antiherpetic drug ganciclovir. Ganciclovir treatment produced complete ablation of parietal cells, dissolution of gastric glands, and loss of chief and mucus-producing cells. Termination of drug treatment led to the reemergence of all major gastric epithelial cell types and restoration of glandular architecture. Our results imply the existence of a pluripotent stem cell for the gastric mucosa. Parietal cell ablation should provide a model for analyzing cell lineage relationships within the stomach as well as mechanisms underlying gastric injury and repair.

  1. Dynamic modeling of plasma-vapor interactions during plasma disruptions

    SciTech Connect

    Hassanein, A.; Ehst, D.A.

    1992-05-01

    Intense deposition of energy in short times on fusion reactor components during a plasma disruption may cause severe surface erosion due to ablation of these components. The exact amount of the eroded material is very important to the reactor design and its lifetime. During the plasma deposition, the vaporized wall material will interact with the incoming plasma particles and may shield the rest of the wall from damage. The vapor shielding may then prolong the lifetime of these components and increase the reactor duty cycle. To correctly evaluate the impact of vapor shielding effect a comprehensive model is developed. In this model the dynamic slowing down of the plasma particles, both ions and electrons, with the eroded wall material is established. Different interaction processes between the plasma particles and the ablated material is included. The generated photons radiation source and the transport of this radiation through the vapor to the wall is modeled. Recent experimental data on disruptions is analyzed and compared with model predictions. Vapor shielding may be effective in reducing the overall erosion rate for certain plasma disruption parameters and conditions.

  2. Influence of the embryonic preplate on the organization of the cerebral cortex: a targeted ablation model.

    PubMed

    Xie, Y; Skinner, E; Landry, C; Handley, V; Schonmann, V; Jacobs, E; Fisher, R; Campagnoni, A

    2002-10-15

    Transgenic mice were generated to permit the targeted ablation of cortical preplate cells at the time they are born. In these mice, the 1.3 kb golli promoter of the myelin basic protein gene was used to drive the herpes simplex virus thymidine kinase (TK) transgene in cortical preplate cells. Heterozygous transgenic pairs were bred, and pregnant dams were treated with ganciclovir at embryonic days 11-12 to ablate preplate cells at the time the preplate was forming. This paradigm exposed control (TK-) and experimental (TK+) littermates to exactly the same conditions. Embryological ablation of preplate cells led to an early disruption of the radial glial framework and subplate structure in the developing cortex and dramatically altered the cellular lamination and connectivity of the cortical plate. The disturbed radial glial network contributed to an impaired radial migration of neurons into the cortical plate from the ventricular zone. The cortical plate became dyslaminated, and there was a substantial reduction in short- and long-range cortical projections within the cortex and to subcortical regions. Cell death within the cortical plate and the proliferative zones was substantially increased in the ablated animals. After birth, a cortical lesion developed, which became exacerbated with the secondary onset of hydrocephaly in the second postnatal week. The results underscore the critical importance of the preplate in cortex formation, mediated through its guidance of the formation of radial glial scaffolding, subsequent neuronal migration into the incipient cortical plate, and the final arrangement of its vertical organization and cellular connectivity.

  3. The Mixed Processing Models Development Of Thermal Fracture And Laser Ablation On Glass Substrate

    NASA Astrophysics Data System (ADS)

    Huang, Kuo-Cheng; Wu, Wen-Hong; Tseng, Shih-Feng; Hwang, Chi-Hung

    2011-01-01

    As the industries of cell phone and LCD TV were vigorously flourishing and the manufacturing requirements for LCD glass substrate were getting higher, the thermal fracture cutting technology (TFCT) has progressively become the main technology for LCD glass substrate cutting. Due to using laser as the heat source, the TFCT has many advantages, such as uniform heating, small heat effect zone, and high cutting speed, smooth cutting surface and low residual stress, etc. Moreover, a general laser ablation processing or traditional diamond wheel cutting does not have the last two advantages. The article presents a mixed processing of glass substrate, which consists of TFCT and laser ablation mechanisms, and how to enhance the cutting speed with little ablation laser energy. In this study, a 10W Nd:YAG laser and a 40W CO2 laser are used as the heat source of TFCT and laser ablation processing, respectively. The result indicates that the speed of the mixed processing is more than twice the speed of TFCT. Furthermore, after the mixed processing, the residual stresses in the glass substrates are also smaller.

  4. Model of THz Magnetization Dynamics

    PubMed Central

    Bocklage, Lars

    2016-01-01

    Magnetization dynamics can be coherently controlled by THz laser excitation, which can be applied in ultrafast magnetization control and switching. Here, transient magnetization dynamics are calculated for excitation with THz magnetic field pulses. We use the ansatz of Smit and Beljers, to formulate dynamic properties of the magnetization via partial derivatives of the samples free energy density, and extend it to solve the Landau-Lifshitz-equation to obtain the THz transients of the magnetization. The model is used to determine the magnetization response to ultrafast multi- and single-cycle THz pulses. Control of the magnetization trajectory by utilizing the THz pulse shape and polarization is demonstrated. PMID:26956997

  5. Structural dynamics system model reduction

    NASA Technical Reports Server (NTRS)

    Chen, J. C.; Rose, T. L.; Wada, B. K.

    1987-01-01

    Loads analysis for structural dynamic systems is usually performed by finite element models. Because of the complexity of the structural system, the model contains large number of degree-of-freedom. The large model is necessary since details of the stress, loads and responses due to mission environments are computed. However, a simplified model is needed for other tasks such as pre-test analysis for modal testing, and control-structural interaction studies. A systematic method of model reduction for modal test analysis is presented. Perhaps it will be of some help in developing a simplified model for the control studies.

  6. Laser diagnostic experiments on KrF laser ablation plasma-plume dynamics relevant to manufacturing applications*

    NASA Astrophysics Data System (ADS)

    Gilgenbach, R. M.; Ching, C. H.; Lash, J. S.; Lindley, R. A.

    1994-05-01

    A brief review is given of the potential applications of laser ablation in the automotive and electronics manufacturing industries. Experiments are presented on KrF laser ablation of three materials relevant to manufacturing applications: aluminum metal vs aluminum-nitride (AlN) and alumina (Al2O3) ceramics. Plasma and neutral-atom diagnostic data are presented from resonant-holographic-interferometry, dye-laser-resonance-absorption photography, and HeNe laser deflection. Data show that plasma electron densities in excess of 1018 cm-3 exist in the ablation of AlN, with lower densities in Al and Al2O3. Aluminum neutral and ion expansion velocities are in the range of cm/μs. Ambipolar electric fields are estimated to be 5-50 V/cm.

  7. Expansion dynamics of laser produced plasma

    SciTech Connect

    Doggett, B.; Lunney, J. G.

    2011-05-01

    We consider the applicability of the isentropic, adiabatic gas dynamical model of plume expansion for laser ablation in vacuum. We show that the model can be applied to ionized plumes and estimate the upper electron temperature limit on the applicability of the isentropic approximation. The model predictions are compared with Langmuir ion probe measurements and deposition profiles obtained for excimer laser ablation of silver.

  8. Cavitation-enhanced nonthermal ablation in deep brain targets: feasibility in a large animal model.

    PubMed

    Arvanitis, Costas D; Vykhodtseva, Natalia; Jolesz, Ferenc; Livingstone, Margaret; McDannold, Nathan

    2016-05-01

    OBJECT Transcranial MRI-guided focused ultrasound (TcMRgFUS) is an emerging noninvasive alternative to surgery and radiosurgery that is undergoing testing for tumor ablation and functional neurosurgery. The method is currently limited to central brain targets due to skull heating and other factors. An alternative ablative approach combines very low intensity ultrasound bursts and an intravenously administered microbubble agent to locally destroy the vasculature. The objective of this work was to investigate whether it is feasible to use this approach at deep brain targets near the skull base in nonhuman primates. METHODS In 4 rhesus macaques, targets near the skull base were ablated using a clinical TcMRgFUS system operating at 220 kHz. Low-duty-cycle ultrasound exposures (sonications) were applied for 5 minutes in conjunction with the ultrasound contrast agent Definity, which was administered as a bolus injection or continuous infusion. The acoustic power level was set to be near the inertial cavitation threshold, which was measured using passive monitoring of the acoustic emissions. The resulting tissue effects were investigated with MRI and with histological analysis performed 3 hours to 1 week after sonication. RESULTS Thirteen targets were sonicated in regions next to the optic tract in the 4 animals. Inertial cavitation, indicated by broadband acoustic emissions, occurred at acoustic pressure amplitudes ranging from 340 to 540 kPa. MRI analysis suggested that the lesions had a central region containing red blood cell extravasations that was surrounded by edema. Blood-brain barrier disruption was observed on contrast-enhanced MRI in the lesions and in a surrounding region corresponding to the prefocal area of the FUS system. In histology, lesions consisting of tissue undergoing ischemic necrosis were found in all regions that were sonicated above the inertial cavitation threshold. Tissue damage in prefocal areas was found in several cases, suggesting that in

  9. IAQ evaluation by dynamic modeling

    SciTech Connect

    Meckler, M.

    1995-12-01

    The current ASHRAE Standard 62-1989, in addition to the ventilation rate (VR) procedure, now contains an alternative procedure in Appendix E to achieve acceptable indoor air quality (IAQ). In this article, the author develops a dynamic model for each of the seven most commonly used HVAC systems listed in Appendix E of ASHRAE Standard 62-1989 and demonstrates how these dynamic models work by providing an illustrative example. In this example, the author estimates the concentration of formaldehyde as a function of time in an office occupancy for three types of filters and outlines how to choose filters to decrease outside air flow requirements.

  10. Global/Local Dynamic Models

    SciTech Connect

    Pfeffer, A; Das, S; Lawless, D; Ng, B

    2006-10-10

    Many dynamic systems involve a number of entities that are largely independent of each other but interact with each other via a subset of state variables. We present global/local dynamic models (GLDMs) to capture these kinds of systems. In a GLDM, the state of an entity is decomposed into a globally influenced state that depends on other entities, and a locally influenced state that depends only on the entity itself. We present an inference algorithm for GLDMs called global/local particle filtering, that introduces the principle of reasoning globally about global dynamics and locally about local dynamics. We have applied GLDMs to an asymmetric urban warfare environment, in which enemy units form teams to attack important targets, and the task is to detect such teams as they form. Experimental results for this application show that global/local particle filtering outperforms ordinary particle filtering and factored particle filtering.

  11. Multiscale modeling of nucleosome dynamics.

    PubMed

    Sharma, Shantanu; Ding, Feng; Dokholyan, Nikolay V

    2007-03-01

    Nucleosomes form the fundamental building blocks of chromatin. Subtle modifications of the constituent histone tails mediate chromatin stability and regulate gene expression. For this reason, it is important to understand structural dynamics of nucleosomes at atomic levels. We report a novel multiscale model of the fundamental chromatin unit, a nucleosome, using a simplified model for rapid discrete molecular dynamics simulations and an all-atom model for detailed structural investigation. Using a simplified structural model, we perform equilibrium simulations of a single nucleosome at various temperatures. We further reconstruct all-atom nucleosome structures from simulation trajectories. We find that histone tails bind to nucleosomal DNA via strong salt-bridge interactions over a wide range of temperatures, suggesting a mechanism of chromatin structural organization whereby histone tails regulate inter- and intranucleosomal assemblies via binding with nucleosomal DNA. We identify specific regions of the histone core H2A/H2B-H4/H3-H3/H4-H2B/H2A, termed "cold sites", which retain a significant fraction of contacts with adjoining residues throughout the simulation, indicating their functional role in nucleosome organization. Cold sites are clustered around H3-H3, H2A-H4 and H4-H2A interhistone interfaces, indicating the necessity of these contacts for nucleosome stability. Essential dynamics analysis of simulation trajectories shows that bending across the H3-H3 is a prominent mode of intranucleosomal dynamics. We postulate that effects of salts on mononucleosomes can be modeled in discrete molecular dynamics by modulating histone-DNA interaction potentials. Local fluctuations in nucleosomal DNA vary significantly along the DNA sequence, suggesting that only a fraction of histone-DNA contacts make strong interactions dominating mononucleosomal dynamics. Our findings suggest that histone tails have a direct functional role in stabilizing higher-order chromatin

  12. Laser ablation inductively coupled plasma dynamic reaction cell mass spectrometry for the multi-element analysis of polymers

    NASA Astrophysics Data System (ADS)

    Resano, M.; García-Ruiz, E.; Vanhaecke, F.

    2005-11-01

    In this work, the potential of laser ablation-inductively coupled plasma-mass spectrometry for the fast analysis of polymers has been explored. Different real-life samples (polyethylene shopping bags, an acrylonitrile butadiene styrene material and various plastic bricks) as well as several reference materials (VDA 001 to 004, Cd in polyethylene) have been selected for the study. Two polyethylene reference materials (ERM-EC 680 and 681), for which a reference or indicative value for the most relevant metals is available, have proved their suitability as standards for calibration. Special attention has been paid to the difficulties expected for the determination of Cr at the μg g - 1 level in this kind of materials, due to the interference of ArC + ions on the most abundant isotopes of Cr. The use of ammonia as a reaction gas in a dynamic reaction cell is shown to alleviate this problem, resulting in a limit of detection of 0.15 μg g - 1 for this element, while limiting only modestly the possibilities of the technique for simultaneous multi-element analysis. In this regard, As is the analyte most seriously affected by the use of ammonia, and its determination has to be carried out in vented mode, at the expense of measuring time. In all cases studied, accurate results could be obtained for elements ranging in content from the sub-μg g - 1 level to tens of thousands of μg g - 1 . However, the use of an element of known concentration as internal standard may be needed for materials with a matrix significantly different from that of the standard (polyethylene in this work). Precision ranged between 5% and 10% RSD for elements found at the 10 μg g - 1 level or higher, while this value could deteriorate to 20% for analytes found at the sub-μg g - 1 level. Overall, the technique evaluated presents many advantages for the fast and accurate multi-element analysis of these materials, avoiding laborious digestion procedures and minimizing the risk of analyte losses due

  13. Modelling of sensitivity of plasmon sensory elements based on silver nanoparticles obtained by laser evaporation and ablation

    NASA Astrophysics Data System (ADS)

    Egorov, V. I.; Sidorov, A. I.

    2016-07-01

    A comparison of the sensitivity of the spectral position of plasmon resonance calculated by numerical methods to a change in the refractive index of the environment for ellipsoidal and spherical silver nanoparticles with a dielectric shell synthesized by laser ablation has been performed. It has been shown that sensitivity is higher for nanoparticles with the shape of a prolate ellipsoid than for spherical nanoparticles. The modeling has shown that the optimal thickness of the dielectric shell should be 10-12 nm and its refractive index should be 1.6. With this, a sensitivity of the plasmon sensor of 32 nm/RIU (RIU is refractive index unit) may be provided.

  14. MR Imaging to Assess Immediate Response to Irreversible Electroporation for Targeted Ablation of Liver Tissues: Preclinical Feasibility Studies in a Rodent Model1

    PubMed Central

    Zhang, Yue; Guo, Yang; Ragin, Ann B.; Lewandowski, Robert J.; Yang, Guang-Yu; Nijm, Grace M.; Sahakian, Alan V.; Omary, Reed A.

    2010-01-01

    Purpose: To test the hypothesis that magnetic resonance (MR) imaging measurements can be used to immediately detect treated tissue regions after irreversible electroporation (IRE) ablation procedures in rodent liver tissues. Materials and Methods: All experiments received institutional animal care and use committee approval. In four rats for preliminary studies and 18 rats for formal assessment, MR imaging–compatible electrodes were inserted into the liver and MR imaging–monitored IRE procedures were performed at one of three electrode voltages (1000, 1500, or 2500 V), with T1- and T2-weighted images acquired before and immediately after application of the IRE pulses. MR imaging measurements were compared with both finite element modeling (FEM)-anticipated ablation zones and histologically confirmed ablation zones at necropsy. Intraclass and Spearman correlation coefficients were calculated for statistical comparisons. Results: MR imaging measurements permitted immediate depiction of IRE ablation zones that were hypointense on T1-weighted images and hyperintense on T2-weighted images. MR imaging–based measurements demonstrated excellent consistency with FEM-anticipated ablation zones (r > 0.90 and P < .001 for both T1- and T2-weighted images). MR imaging measurements were also highly correlated with histologically confirmed ablation zone measurements (ρ > 0.90 and P < .001 for both T1- and T2-weighted images). Conclusion: MR imaging permits immediate depiction of ablated tissue zones for monitoring of IRE ablation procedures. These measurements could potentially be used during treatment to elicit repeat application of IRE pulses or adjustments to electrode positions to ensure complete treatment of targeted lesions. © RSNA, 2010 PMID:20656834

  15. Interactive real-time mapping and catheter ablation of the cavotricuspid isthmus guided by magnetic resonance imaging in a porcine model

    PubMed Central

    Hoffmann, Boris A.; Koops, Andreas; Rostock, Thomas; Müllerleile, Kai; Steven, Daniel; Karst, Roman; Steinke, Mark U.; Drewitz, Imke; Lund, Gunnar; Koops, Susan; Adam, Gerhard; Willems, Stephan

    2010-01-01

    Aims We investigated the feasibility of real-time magnetic resonance imaging (RTMRI) guided ablation of the cavotricuspid isthmus (CTI) by using a MRI-compatible ablation catheter. Methods and results Cavotricuspid isthmus ablation was performed in an interventional RTMRI suite by using a novel 7 French, steerable, non-ferromagnetic ablation catheter in a porcine in vivo model (n = 20). The catheter was introduced and navigated by RTMRI visualization only. Catheter position and movement during manipulation were continuously visualized during the entire intervention. Two porcine prematurely died due to VT/VF. Anatomical completion of the CTI ablation line could be achieved after a mean of 6.3±3 RF pulses (RF energy: 1807±1016.4 Ws/RF pulse, temperature: 55.9±5.9°C) in n = 18 animals. In 15 of 18 procedures (83.3%) a complete CTI block was proven by conventional mapping in the electrophysiological (EP) lab. Conclusion Completely non-fluoroscopic ablation guided by RTMRI using a steerable and non-ferromagnetic catheter is a promising novel technology in interventional electrophysiology. PMID:19897495

  16. Predictive models of battle dynamics

    NASA Astrophysics Data System (ADS)

    Jelinek, Jan

    2001-09-01

    The application of control and game theories to improve battle planning and execution requires models, which allow military strategists and commanders to reliably predict the expected outcomes of various alternatives over a long horizon into the future. We have developed probabilistic battle dynamics models, whose building blocks in the form of Markov chains are derived from the first principles, and applied them successfully in the design of the Model Predictive Task Commander package. This paper introduces basic concepts of our modeling approach and explains the probability distributions needed to compute the transition probabilities of the Markov chains.

  17. Observability in dynamic evolutionary models.

    PubMed

    López, I; Gámez, M; Carreño, R

    2004-02-01

    In the paper observability problems are considered in basic dynamic evolutionary models for sexual and asexual populations. Observability means that from the (partial) knowledge of certain phenotypic characteristics the whole evolutionary process can be uniquely recovered. Sufficient conditions are given to guarantee observability for both sexual and asexual populations near an evolutionarily stable state.

  18. Nonlinear Dynamic Model Explains The Solar Dynamic

    NASA Astrophysics Data System (ADS)

    Kuman, Maria

    Nonlinear mathematical model in torus representation describes the solar dynamic. Its graphic presentation shows that without perturbing force the orbits of the planets would be circles; only perturbing force could elongate the circular orbits into ellipses. Since the Hubble telescope found that the planetary orbits of other stars in the Milky Way are also ellipses, powerful perturbing force must be present in our galaxy. Such perturbing force is the Sagittarius Dwarf Galaxy with its heavy Black Hole and leftover stars, which we see orbiting around the center of our galaxy. Since observations of NASA's SDO found that magnetic fields rule the solar activity, we can expect when the planets align and their magnetic moments sum up, the already perturbed stars to reverse their magnetic parity (represented graphically as periodic looping through the hole of the torus). We predict that planets aligned on both sides of the Sun, when their magnetic moments sum-up, would induce more flares in the turbulent equatorial zone, which would bulge. When planets align only on one side of the Sun, the strong magnetic gradient of their asymmetric pull would flip the magnetic poles of the Sun. The Sun would elongate pole-to-pole, emit some energy through the poles, and the solar activity would cease. Similar reshaping and emission was observed in stars called magnetars and experimentally observed in super-liquid fast-spinning Helium nanodroplets. We are certain that NASA's SDO will confirm our predictions.

  19. The Annual Glaciohydrology Cycle in the Ablation Zone of the Greenland Ice Sheet: Part 1. Hydrology Model

    NASA Technical Reports Server (NTRS)

    Colgan, William; Rajaram, Harihar; Anderson, Robert; Steffen. Konrad; Phillips, Thomas; Zwally, H. Jay; Abdalati, Waleed

    2012-01-01

    We apply a novel one-dimensional glacier hydrology model that calculates hydraulic head to the tidewater-terminating Sermeq Avannarleq flowline of the Greenland ice sheet. Within a plausible parameter space, the model achieves a quasi-steady-state annual cycle in which hydraulic head oscillates close to flotation throughout the ablation zone. Flotation is briefly achieved during the summer melt season along a approx.17 km stretch of the approx.50 km of flowline within the ablation zone. Beneath the majority of the flowline, subglacial conduit storage closes (i.e. obtains minimum radius) during the winter and opens (i.e. obtains maximum radius) during the summer. Along certain stretches of the flowline, the model predicts that subglacial conduit storage remains open throughout the year. A calculated mean glacier water residence time of approx.2.2 years implies that significant amounts of water are stored in the glacier throughout the year. We interpret this residence time as being indicative of the timescale over which the glacier hydrologic system is capable of adjusting to external surface meltwater forcings. Based on in situ ice velocity observations, we suggest that the summer speed-up event generally corresponds to conditions of increasing hydraulic head during inefficient subglacial drainage. Conversely, the slowdown during fall generally corresponds to conditions of decreasing hydraulic head during efficient subglacial drainage.

  20. Nanoparticle generation and transport resulting from femtosecond laser ablation of ultrathin metal films: Time-resolved measurements and molecular dynamics simulations

    SciTech Connect

    Rouleau, C. M. Puretzky, A. A.; Geohegan, D. B.; Shih, C.-Y.; Wu, C.; Zhigilei, L. V.

    2014-05-12

    The synthesis of metal nanoparticles by ultrafast laser ablation of nanometers-thick metal films has been studied experimentally and computationally. Near-threshold backside laser ablation of 2–20 nm-thick Pt films deposited on fused silica substrates was found to produce nanoparticles with size distributions that were bimodal for the thicker films, but collapsed into a single mode distribution for the thinnest film. Time-resolved imaging of blackbody emission from the Pt nanoparticles was used to reveal the nanoparticle propagation dynamics and estimate their temperatures. The observed nanoparticle plume was compact and highly forward-directed with a well-defined collective velocity that permitted multiple rebounds with substrates to be revealed. Large-scale molecular dynamics simulations were used to understand the evolution of compressive and tensile stresses in the thicker melted liquid films that lead to their breakup and ejection of two groups of nanoparticles with different velocity and size distributions. Ultrafast laser irradiation of ultrathin (few nm) metal films avoids the splitting of the film and appears to be a method well-suited to cleanly synthesize and deposit nanoparticles from semitransparent thin film targets in highly directed beams.

  1. Characterization of tracked radiofrequency ablation in phantom

    SciTech Connect

    Chen, Chun-Cheng R.; Miga, Michael I.; Galloway, Robert L.

    2007-10-15

    In radiofrequency ablation (RFA), successful therapy requires accurate, image-guided placement of the ablation device in a location selected by a predictive treatment plan. Current planning methods rely on geometric models of ablations that are not sensitive to underlying physical processes in RFA. Implementing plans based on computational models of RFA with image-guided techniques, however, has not been well characterized. To study the use of computational models of RFA in planning needle placement, this work compared ablations performed with an optically tracked RFA device with corresponding models of the ablations. The calibration of the tracked device allowed the positions of distal features of the device, particularly the tips of the needle electrodes, to be determined to within 1.4{+-}0.6 mm of uncertainty. Ablations were then performed using the tracked device in a phantom system based on an agarose-albumin mixture. Images of the sliced phantom obtained from the ablation experiments were then compared with the predictions of a bioheat transfer model of RFA, which used the positional data of the tracked device obtained during ablation. The model was demonstrated to predict 90% of imaged pixels classified as being ablated. The discrepancies between model predictions and observations were analyzed and attributed to needle tracking inaccuracy as well as to uncertainties in model parameters. The results suggest the feasibility of using finite element modeling to plan ablations with predictable outcomes when implemented using tracked RFA.

  2. Dynamical Modelling of Meteoroid Streams

    NASA Astrophysics Data System (ADS)

    Clark, David; Wiegert, P. A.

    2012-10-01

    Accurate simulations of meteoroid streams permit the prediction of stream interaction with Earth, and provide a measure of risk to Earth satellites and interplanetary spacecraft. Current cometary ejecta and meteoroid stream models have been somewhat successful in predicting some stream observations, but have required questionable assumptions and significant simplifications. Extending on the approach of Vaubaillon et al. (2005)1, we model dust ejection from the cometary nucleus, and generate sample particles representing bins of distinct dynamical evolution-regulating characteristics (size, density, direction, albedo). Ephemerides of the sample particles are integrated and recorded for later assignment of frequency based on model parameter changes. To assist in model analysis we are developing interactive software to permit the “turning of knobs” of model parameters, allowing for near-real-time 3D visualization of resulting stream structure. With this tool, we will revisit prior assumptions made, and will observe the impact of introducing non-uniform cometary surface attributes and temporal activity. The software uses a single model definition and implementation throughout model verification, sample particle bin generation and integration, and analysis. It supports the adjustment with feedback of both independent and independent model values, with the intent of providing an interface supporting multivariate analysis. Propagations of measurement uncertainties and model parameter precisions are tracked rigorously throughout. We maintain a separation of the model itself from the abstract concepts of model definition, parameter manipulation, and real-time analysis and visualization. Therefore we are able to quickly adapt to fundamental model changes. It is hoped the tool will also be of use in other solar system dynamics problems. 1 Vaubaillon, J.; Colas, F.; Jorda, L. (2005) A new method to predict meteor showers. I. Description of the model. Astronomy and

  3. Modulation of Neural Network Activity through Single Cell Ablation: An in Vitro Model of Minimally Invasive Neurosurgery.

    PubMed

    Soloperto, Alessandro; Bisio, Marta; Palazzolo, Gemma; Chiappalone, Michela; Bonifazi, Paolo; Difato, Francesco

    2016-01-01

    The technological advancement of optical approaches, and the growth of their applications in neuroscience, has allowed investigations of the physio-pathology of neural networks at a single cell level. Therefore, better understanding the role of single neurons in the onset and progression of neurodegenerative conditions has resulted in a strong demand for surgical tools operating with single cell resolution. Optical systems already provide subcellular resolution to monitor and manipulate living tissues, and thus allow understanding the potentiality of surgery actuated at single cell level. In the present work, we report an in vitro experimental model of minimally invasive surgery applied on neuronal cultures expressing a genetically encoded calcium sensor. The experimental protocol entails the continuous monitoring of the network activity before and after the ablation of a single neuron, to provide a robust evaluation of the induced changes in the network activity. We report that in subpopulations of about 1000 neurons, even the ablation of a single unit produces a reduction of the overall network activity. The reported protocol represents a simple and cost effective model to study the efficacy of single-cell surgery, and it could represent a test-bed to study surgical procedures circumventing the abrupt and complete tissue removal in pathological conditions. PMID:27527143

  4. Modulation of Neural Network Activity through Single Cell Ablation: An in Vitro Model of Minimally Invasive Neurosurgery.

    PubMed

    Soloperto, Alessandro; Bisio, Marta; Palazzolo, Gemma; Chiappalone, Michela; Bonifazi, Paolo; Difato, Francesco

    2016-01-01

    The technological advancement of optical approaches, and the growth of their applications in neuroscience, has allowed investigations of the physio-pathology of neural networks at a single cell level. Therefore, better understanding the role of single neurons in the onset and progression of neurodegenerative conditions has resulted in a strong demand for surgical tools operating with single cell resolution. Optical systems already provide subcellular resolution to monitor and manipulate living tissues, and thus allow understanding the potentiality of surgery actuated at single cell level. In the present work, we report an in vitro experimental model of minimally invasive surgery applied on neuronal cultures expressing a genetically encoded calcium sensor. The experimental protocol entails the continuous monitoring of the network activity before and after the ablation of a single neuron, to provide a robust evaluation of the induced changes in the network activity. We report that in subpopulations of about 1000 neurons, even the ablation of a single unit produces a reduction of the overall network activity. The reported protocol represents a simple and cost effective model to study the efficacy of single-cell surgery, and it could represent a test-bed to study surgical procedures circumventing the abrupt and complete tissue removal in pathological conditions.

  5. Dynamic Model of Mesoscale Eddies

    NASA Astrophysics Data System (ADS)

    Dubovikov, Mikhail S.

    2003-04-01

    Oceanic mesoscale eddies which are analogs of well known synoptic eddies (cyclones and anticyclones), are studied on the basis of the turbulence model originated by Dubovikov (Dubovikov, M.S., "Dynamical model of turbulent eddies", Int. J. Mod. Phys.B7, 4631-4645 (1993).) and further developed by Canuto and Dubovikov (Canuto, V.M. and Dubovikov, M.S., "A dynamical model for turbulence: I. General formalism", Phys. Fluids8, 571-586 (1996a) (CD96a); Canuto, V.M. and Dubovikov, M.S., "A dynamical model for turbulence: II. Sheardriven flows", Phys. Fluids8, 587-598 (1996b) (CD96b); Canuto, V.M., Dubovikov, M.S., Cheng, Y. and Dienstfrey, A., "A dynamical model for turbulence: III. Numerical results", Phys. Fluids8, 599-613 (1996c)(CD96c); Canuto, V.M., Dubovikov, M.S. and Dienstfrey, A., "A dynamical model for turbulence: IV. Buoyancy-driven flows", Phys. Fluids9, 2118-2131 (1997a) (CD97a); Canuto, V.M. and Dubovikov, M.S., "A dynamical model for turbulence: V. The effect of rotation", Phys. Fluids9, 2132-2140 (1997b) (CD97b); Canuto, V.M., Dubovikov, M.S. and Wielaard, D.J., "A dynamical model for turbulence: VI. Two dimensional turbulence", Phys. Fluids9, 2141-2147 (1997c) (CD97c); Canuto, V.M. and Dubovikov, M.S., "Physical regimes and dimensional structure of rotating turbulence", Phys. Rev. Lett. 78, 666-669 (1997d) (CD97d); Canuto, V.M., Dubovikov, M.S. and Dienstfrey, A., "Turbulent convection in a spectral model", Phys. Rev. Lett. 78, 662-665 (1997e) (CD97e); Canuto, V.M. and Dubovikov, M.S., "A new approach to turbulence", Int. J. Mod. Phys.12, 3121-3152 (1997f) (CD97f); Canuto, V.M. and Dubovikov, M.S., "Two scaling regimes for rotating Raleigh-Benard convection", Phys. Rev. Letters78, 281-284, (1998) (CD98); Canuto, V.M. and Dubovikov, M.S., "A dynamical model for turbulence: VII. The five invariants for shear driven flows", Phys. Fluids11, 659-664 (1999a) (CD99a); Canuto, V.M., Dubovikov, M.S. and Yu, G., "A dynamical model for turbulence: VIII. IR and UV

  6. Modelling MIZ dynamics in a global model

    NASA Astrophysics Data System (ADS)

    Rynders, Stefanie; Aksenov, Yevgeny; Feltham, Daniel; Nurser, George; Naveira Garabato, Alberto

    2016-04-01

    Exposure of large, previously ice-covered areas of the Arctic Ocean to the wind and surface ocean waves results in the Arctic pack ice cover becoming more fragmented and mobile, with large regions of ice cover evolving into the Marginal Ice Zone (MIZ). The need for better climate predictions, along with growing economic activity in the Polar Oceans, necessitates climate and forecasting models that can simulate fragmented sea ice with a greater fidelity. Current models are not fully fit for the purpose, since they neither model surface ocean waves in the MIZ, nor account for the effect of floe fragmentation on drag, nor include sea ice rheology that represents both the now thinner pack ice and MIZ ice dynamics. All these processes affect the momentum transfer to the ocean. We present initial results from a global ocean model NEMO (Nucleus for European Modelling of the Ocean) coupled to the Los Alamos sea ice model CICE. The model setup implements a novel rheological formulation for sea ice dynamics, accounting for ice floe collisions, thus offering a seamless framework for pack ice and MIZ simulations. The effect of surface waves on ice motion is included through wave pressure and the turbulent kinetic energy of ice floes. In the multidecadal model integrations we examine MIZ and basin scale sea ice and oceanic responses to the changes in ice dynamics. We analyse model sensitivities and attribute them to key sea ice and ocean dynamical mechanisms. The results suggest that the effect of the new ice rheology is confined to the MIZ. However with the current increase in summer MIZ area, which is projected to continue and may become the dominant type of sea ice in the Arctic, we argue that the effects of the combined sea ice rheology will be noticeable in large areas of the Arctic Ocean, affecting sea ice and ocean. With this study we assert that to make more accurate sea ice predictions in the changing Arctic, models need to include MIZ dynamics and physics.

  7. On whole Abelian model dynamics

    SciTech Connect

    Chauca, J.; Doria, R.

    2012-09-24

    Physics challenge is to determine the objects dynamics. However, there are two ways for deciphering the part. The first one is to search for the ultimate constituents; the second one is to understand its behaviour in whole terms. Therefore, the parts can be defined either from elementary constituents or as whole functions. Historically, science has been moving through the first aspect, however, quarks confinement and complexity are interrupting this usual approach. These relevant facts are supporting for a systemic vision be introduced. Our effort here is to study on the whole meaning through gauge theory. Consider a systemic dynamics oriented through the U(1) - systemic gauge parameter which function is to collect a fields set {l_brace}A{sub {mu}I}{r_brace}. Derive the corresponding whole gauge invariant Lagrangian, equations of motion, Bianchi identities, Noether relationships, charges and Ward-Takahashi equations. Whole Lorentz force and BRST symmetry are also studied. These expressions bring new interpretations further than the usual abelian model. They are generating a systemic system governed by 2N+ 10 classical equations plus Ward-Takahashi identities. A whole dynamics based on the notions of directive and circumstance is producing a set determinism where the parts dynamics are inserted in the whole evolution. A dynamics based on state, collective and individual equations with a systemic interdependence.

  8. Modeling wildfire incident complexity dynamics.

    PubMed

    Thompson, Matthew P

    2013-01-01

    Wildfire management in the United States and elsewhere is challenged by substantial uncertainty regarding the location and timing of fire events, the socioeconomic and ecological consequences of these events, and the costs of suppression. Escalating U.S. Forest Service suppression expenditures is of particular concern at a time of fiscal austerity as swelling fire management budgets lead to decreases for non-fire programs, and as the likelihood of disruptive within-season borrowing potentially increases. Thus there is a strong interest in better understanding factors influencing suppression decisions and in turn their influence on suppression costs. As a step in that direction, this paper presents a probabilistic analysis of geographic and temporal variation in incident management team response to wildfires. The specific focus is incident complexity dynamics through time for fires managed by the U.S. Forest Service. The modeling framework is based on the recognition that large wildfire management entails recurrent decisions across time in response to changing conditions, which can be represented as a stochastic dynamic system. Daily incident complexity dynamics are modeled according to a first-order Markov chain, with containment represented as an absorbing state. A statistically significant difference in complexity dynamics between Forest Service Regions is demonstrated. Incident complexity probability transition matrices and expected times until containment are presented at national and regional levels. Results of this analysis can help improve understanding of geographic variation in incident management and associated cost structures, and can be incorporated into future analyses examining the economic efficiency of wildfire management.

  9. Model to predict the melting and ablation of reactive metal shrapnel in a high Weber number environment

    SciTech Connect

    Connell, L.W.

    1984-05-01

    Aerothermoballistic behavior of pyrophoric metal shrapnel ejected at supersonic speeds has been numerically simulated. The theoretical model predicts aerodynamic and chemical heat-transfer rates and particle thermal response, including time and position of melt initiation. Because of the high Weber number environment, the melting particle undergoes liquid layer stripping. The model, incorporated in the PLUTO computer code, predicts the liquid mass loss rate, characteristic liquid droplet diameter, temperature rise across the liquid film, and the coupled particle trajectory. The aeroheating, thermal, and ballistic sections of the PLUTO code have been validated by comparison with independent calculations and qualitative experimental data concerning the melting and ablation of gold microspheres. The model still needs to be field tested against reactive metal particles in high Weber number flows.

  10. Laser ablation of Al-Ni alloys and multilayers

    NASA Astrophysics Data System (ADS)

    Roth, Johannes; Trebin, Hans-Rainer; Kiselev, Alexander; Rapp, Dennis-Michael

    2016-05-01

    Laser ablation of Al-Ni alloys and multilayers has been studied by molecular dynamics simulations. The method was combined with a two-temperature model to describe the interaction between the laser beam, the electrons, and the atoms. As a first step, electronic parameters for the alloys had to be found and the model developed originally for pure metals had to be generalized to multilayers. The modifications were verified by computing melting depths and ablation thresholds for pure Al and Ni. Here known data could be reproduced. The improved model was applied to the alloys Al_3Ni, AlNi and AlNi_3. While melting depths and ablation thresholds for AlNi behave unspectacular, sharp drops at high fluences are observed for Al_3Ni and AlNi_3. In both cases, the reason is a change in ablation mechanism from phase explosion to vaporization. Furthermore, a phase transition occurs in Al_3Ni. Finally, Al layers of various thicknesses on a Ni substrate have been simulated. Above threshold, 8 nm Al films are ablated as a whole while 24 nm Al films are only partially removed. Below threshold, alloying with a mixture gradient has been observed in the thin layer system.

  11. Quantifying Post- Laser Ablation Prostate Therapy Changes on MRI via a Domain-Specific Biomechanical Model: Preliminary Findings

    PubMed Central

    Toth, Robert; Sperling, Dan; Madabhushi, Anant

    2016-01-01

    Focal laser ablation destroys cancerous cells via thermal destruction of tissue by a laser. Heat is absorbed, causing thermal necrosis of the target region. It combines the aggressive benefits of radiation treatment (destroying cancer cells) without the harmful side effects (due to its precise localization). MRI is typically used pre-treatment to determine the targeted area, and post-treatment to determine efficacy by detecting necrotic tissue, or tumor recurrence. However, no system exists to quantitatively evaluate the post-treatment effects on the morphology and structure via MRI. To quantify these changes, the pre- and post-treatment MR images must first be spatially aligned. The goal is to quantify (a) laser-induced shape-based changes, and (b) changes in MRI parameters post-treatment. The shape-based changes may be correlated with treatment efficacy, and the quantitative effects of laser treatment over time is currently poorly understood. This work attempts to model changes in gland morphology following laser treatment due to (1) patient alignment, (2) changes due to surrounding organs such as the bladder and rectum, and (3) changes due to the treatment itself. To isolate the treatment-induced shape-based changes, the changes from (1) and (2) are first modeled and removed using a finite element model (FEM). A FEM models the physical properties of tissue. The use of a physical biomechanical model is important since a stated goal of this work is to determine the physical shape-based changes to the prostate from the treatment, and therefore only physical real deformations are to be allowed. A second FEM is then used to isolate the physical, shape-based, treatment-induced changes. We applied and evaluated our model in capturing the laser induced changes to the prostate morphology on eight patients with 3.0 Tesla, T2-weighted MRI, acquired approximately six months following treatment. Our results suggest the laser treatment causes a decrease in prostate volume

  12. Quantifying Post- Laser Ablation Prostate Therapy Changes on MRI via a Domain-Specific Biomechanical Model: Preliminary Findings.

    PubMed

    Toth, Robert; Sperling, Dan; Madabhushi, Anant

    2016-01-01

    Focal laser ablation destroys cancerous cells via thermal destruction of tissue by a laser. Heat is absorbed, causing thermal necrosis of the target region. It combines the aggressive benefits of radiation treatment (destroying cancer cells) without the harmful side effects (due to its precise localization). MRI is typically used pre-treatment to determine the targeted area, and post-treatment to determine efficacy by detecting necrotic tissue, or tumor recurrence. However, no system exists to quantitatively evaluate the post-treatment effects on the morphology and structure via MRI. To quantify these changes, the pre- and post-treatment MR images must first be spatially aligned. The goal is to quantify (a) laser-induced shape-based changes, and (b) changes in MRI parameters post-treatment. The shape-based changes may be correlated with treatment efficacy, and the quantitative effects of laser treatment over time is currently poorly understood. This work attempts to model changes in gland morphology following laser treatment due to (1) patient alignment, (2) changes due to surrounding organs such as the bladder and rectum, and (3) changes due to the treatment itself. To isolate the treatment-induced shape-based changes, the changes from (1) and (2) are first modeled and removed using a finite element model (FEM). A FEM models the physical properties of tissue. The use of a physical biomechanical model is important since a stated goal of this work is to determine the physical shape-based changes to the prostate from the treatment, and therefore only physical real deformations are to be allowed. A second FEM is then used to isolate the physical, shape-based, treatment-induced changes. We applied and evaluated our model in capturing the laser induced changes to the prostate morphology on eight patients with 3.0 Tesla, T2-weighted MRI, acquired approximately six months following treatment. Our results suggest the laser treatment causes a decrease in prostate volume

  13. Pulsed laser ablation of complex oxides: The role of congruent ablation and preferential scattering for the film stoichiometry

    SciTech Connect

    Wicklein, S.; Koehl, A.; Dittmann, R.; Sambri, A.; Amoruso, S.; Wang, X.; Bruzzese, R.

    2012-09-24

    By combining structural and chemical thin film analysis with detailed plume diagnostics and modeling of the laser plume dynamics, we are able to elucidate the different physical mechanisms determining the stoichiometry of the complex oxides model material SrTiO{sub 3} during pulsed laser deposition. Deviations between thin film and target stoichiometry are basically a result of two effects, namely, incongruent ablation and preferential scattering of lighter ablated species during their motion towards the substrate in the O{sub 2} background gas. On the one hand, a progressive preferential ablation of the Ti species with increasing laser fluence leads to a regime of Ti-rich thin film growth at larger fluences. On the other hand, in the low laser fluence regime, a more effective scattering of the lighter Ti plume species results in Sr rich films.

  14. Evolution models with extremal dynamics.

    PubMed

    Kärenlampi, Petri P

    2016-08-01

    The random-neighbor version of the Bak-Sneppen biological evolution model is reproduced, along with an analogous model of random replicators, the latter eventually experiencing topology changes. In the absence of topology changes, both types of models self-organize to a critical state. Species extinctions in the replicator system degenerates the self-organization to a random walk, as does vanishing of species interaction for the BS-model. A replicator model with speciation is introduced, experiencing dramatic topology changes. It produces a variety of features, but self-organizes to a possibly critical state only in a few special cases. Speciation-extinction dynamics interfering with self-organization, biological macroevolution probably is not a self-organized critical system. PMID:27626090

  15. Dynamical modelling of meteoroid streams

    NASA Astrophysics Data System (ADS)

    Clark, D. L.; Wiegert, P. A.

    2014-07-01

    Accurate simulations of meteoroid streams permit the prediction of stream interaction with Earth, and provide a measure of risk to Earth satellites and interplanetary spacecraft. Current cometary ejecta and meteoroid stream models have been somewhat successful in predicting some stream observations, but have required significant assumptions and simplifications. Extending on the approach of Vaubaillon et al. 2005, we model dust ejection from the cometary nucleus, and generate sample particles representing bins of distinct dynamical evolution-regulating characteristics (size, density, direction, albedo). Ephemerides of the sample particles are integrated and recorded for later assignment of weights based on model parameter changes. To assist in model analysis we are developing interactive software to permit the "turning of knobs" of model parameters, allowing for near-real-time 3D visualization of resulting stream structure. Using the tool, we will revisit prior assumptions made, and will observe the impact of introducing non-uniform and time-variant cometary surface attributes and processes.

  16. Ablation of sensory neurons in a genetic model of pancreatic ductal adenocarcinoma slows initiation and progression of cancer.

    PubMed

    Saloman, Jami L; Albers, Kathryn M; Li, Dongjun; Hartman, Douglas J; Crawford, Howard C; Muha, Emily A; Rhim, Andrew D; Davis, Brian M

    2016-03-15

    Pancreatic ductal adenocarcinoma (PDAC) is characterized by an exuberant inflammatory desmoplastic response. The PDAC microenvironment is complex, containing both pro- and antitumorigenic elements, and remains to be fully characterized. Here, we show that sensory neurons, an under-studied cohort of the pancreas tumor stroma, play a significant role in the initiation and progression of the early stages of PDAC. Using a well-established autochthonous model of PDAC (PKC), we show that inflammation and neuronal damage in the peripheral and central nervous system (CNS) occurs as early as the pancreatic intraepithelial neoplasia (PanIN) 2 stage. Also at the PanIN2 stage, pancreas acinar-derived cells frequently invade along sensory neurons into the spinal cord and migrate caudally to the lower thoracic and upper lumbar regions. Sensory neuron ablation by neonatal capsaicin injection prevented perineural invasion (PNI), astrocyte activation, and neuronal damage, suggesting that sensory neurons convey inflammatory signals from Kras-induced pancreatic neoplasia to the CNS. Neuron ablation in PKC mice also significantly delayed PanIN formation and ultimately prolonged survival compared with vehicle-treated controls (median survival, 7.8 vs. 4.5 mo; P = 0.001). These data establish a reciprocal signaling loop between the pancreas and nervous system, including the CNS, that supports inflammation associated with oncogenic Kras-induced neoplasia. Thus, pancreatic sensory neurons comprise an important stromal cell population that supports the initiation and progression of PDAC and may represent a potential target for prevention in high-risk populations.

  17. Developing the model of laser ablation by considering the interplay between emission and expansion of aluminum plasma

    SciTech Connect

    Rezaei, F.; Tavassoli, S. H.

    2013-01-15

    In the present study, the ablation behavior of aluminum target and its plasma radiation in noble ambient gases by a laser pulse with wavelength of 266 nm and pulse duration of 10 ns are numerically studied. A thermal model of laser ablation considering heat conduction, Euler equations, Saha-Eggert equations, Knudsen layer, mass and energy balance relations and optical shielding effects are used for calculation of plasma parameters. Effects of excitation energy on plasma expansion and its emissivity are investigated. Time and spatial-resolved plasma emission including bremsstrahlung, recombination and spectral emission at early delay times after laser irradiation is obtained. Effects of two ambient gases (He and Ar) as well as different gas pressures of 100, 300, 500, and 760 Torr on plasma expansion and its spectrum are studied. Results illustrate that at initial delay times, especially at high noble gas pressures, ionic lines have the maximum intensities, while at later times neutral lines dominate. When the pressure of ambient gas increases, a confinement of the plasma plume is predicted and the intensity of neutral lines decreases. Continuous emission increases with wavelength in both ambient gases. Spatially resolved analysis shows that an intense continuous emission is predicted next to the sample surface decreasing with distance from the latter.

  18. Modelling distributed glacier ablation on Haut Glacier d'Arolla, Switzerland: a comparison of an energy-balance and an enhanced temperature-index model

    NASA Astrophysics Data System (ADS)

    Carenzo, Marco; Pellicciotti, Francesca; Helbing, Jakob; Dadic, Ruzica; Burlando, Paolo

    2010-05-01

    Modelling melt rates across alpine glaciers is an essential step for studying the interannual evolution of snow-cover and glacier ice and for estimation of the total runoff from glacierised basins. Two approaches are commonly used to compute melt: physically-based energy-balance models in which each of the relevant energy fluxes at the glacier-surface interface is computed using energy-balance equations and more empirical temperature-index models in which melt is calculated as a linear function of air temperature. The latter method has been recently improved by including additional variables, in order to bridge the gap between the two approaches and combine the lower data requirement of the latter with the higher accuracy of the former. Comparison between the two methods has been often conducted at the point scale, but very few such studies exist at the glacier wide-scale. The main aim of this paper is to compare predictive skills and limitations of the two approaches at the distributed scale when input data from both on and off-glacier Automatic Weather Stations (AWSs) are used. For this purpose, we compute distributed ablation on Haut Glacier d'Arolla, Switzerland, by means of a physically-based energy-balance (EB) model and an enhanced temperature-index model (ETI), for the ablation seasons 2001 and 2006. Meteorological measurements from AWSs located on and off-glacier are extrapolated to the distributed glacier-wide scale using various extrapolation techniques. A parametric model that includes the effect of shading, atmospheric transmittance and reflection from slopes is used for modelling shortwave radiation. In the EB model, the longwave radiation flux is computed by means of Stefan-Boltzmann relationships and turbulent fluxes are calculated using the bulk aerodynamic method. Subsurface heat conduction are also included. Hourly melt rates are validated against ablation observations derived from an ultrasonic depth gauge and ablation stakes (point scale) and

  19. Simulated evaluation of an intraoperative surface modeling method for catheter ablation by a real phantom simulation experiment

    NASA Astrophysics Data System (ADS)

    Sun, Deyu; Rettmann, Maryam E.; Packer, Douglas; Robb, Richard A.; Holmes, David R.

    2015-03-01

    In this work, we propose a phantom experiment method to quantitatively evaluate an intraoperative left-atrial modeling update method. In prior work, we proposed an update procedure which updates the preoperative surface model with information from real-time tracked 2D ultrasound. Prior studies did not evaluate the reconstruction using an anthropomorphic phantom. In this approach, a silicone heart phantom (based on a high resolution human atrial surface model reconstructed from CT images) was made as simulated atriums. A surface model of the left atrium of the phantom was deformed by a morphological operation - simulating the shape difference caused by organ deformation between pre-operative scanning and intra-operative guidance. During the simulated procedure, a tracked ultrasound catheter was inserted into right atrial phantom - scanning the left atrial phantom in a manner mimicking the cardiac ablation procedure. By merging the preoperative model and the intraoperative ultrasound images, an intraoperative left atrial model was reconstructed. According to results, the reconstruction error of the modeling method is smaller than the initial geometric difference caused by organ deformation. As the area of the left atrial phantom scanned by ultrasound increases, the reconstruction error of the intraoperative surface model decreases. The study validated the efficacy of the modeling method.

  20. Modeling Wildfire Incident Complexity Dynamics

    PubMed Central

    Thompson, Matthew P.

    2013-01-01

    Wildfire management in the United States and elsewhere is challenged by substantial uncertainty regarding the location and timing of fire events, the socioeconomic and ecological consequences of these events, and the costs of suppression. Escalating U.S. Forest Service suppression expenditures is of particular concern at a time of fiscal austerity as swelling fire management budgets lead to decreases for non-fire programs, and as the likelihood of disruptive within-season borrowing potentially increases. Thus there is a strong interest in better understanding factors influencing suppression decisions and in turn their influence on suppression costs. As a step in that direction, this paper presents a probabilistic analysis of geographic and temporal variation in incident management team response to wildfires. The specific focus is incident complexity dynamics through time for fires managed by the U.S. Forest Service. The modeling framework is based on the recognition that large wildfire management entails recurrent decisions across time in response to changing conditions, which can be represented as a stochastic dynamic system. Daily incident complexity dynamics are modeled according to a first-order Markov chain, with containment represented as an absorbing state. A statistically significant difference in complexity dynamics between Forest Service Regions is demonstrated. Incident complexity probability transition matrices and expected times until containment are presented at national and regional levels. Results of this analysis can help improve understanding of geographic variation in incident management and associated cost structures, and can be incorporated into future analyses examining the economic efficiency of wildfire management. PMID:23691014

  1. Hydra modeling of the effect of nearly complete inflight ice and ablator mix in a NIF implosion on several key diagnostics

    NASA Astrophysics Data System (ADS)

    Kritcher, Andrea; Sepke, Scott; Scott, Howard; Regan, Sean; Masse, Laurent; Raman, Kumar; Grim, Gary; Cerjan, Charlie; Marinak, Marty; Spears, Brian; Meezan, Nathan; Suter, Larry

    2012-10-01

    A programmed mix model is used with the radiation hydrodynamics code HYDRA to explore the effects of nearly complete inflight mixing of the ice and ablator on NIC implosion performance and diagnostic signatures. In NIC DT implosions, nearly complete mix of the DT ice and ablator can be envisioned via cold jets of material penetrating the ice possibly combined with turbulence at the fuel-ablator interface. The quantitative impact of this scenario on several key NIF diagnostics, including yield, ion temperature, downscattered neutron spectrum, neutron imaging, Ge and Cu atomic emission analysis, gated x-ray imaging, and streaked x-ray radiography will be discussed. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-564191.

  2. Data modeling of network dynamics

    NASA Astrophysics Data System (ADS)

    Jaenisch, Holger M.; Handley, James W.; Faucheux, Jeffery P.; Harris, Brad

    2004-01-01

    This paper highlights Data Modeling theory and its use for text data mining as a graphical network search engine. Data Modeling is then used to create a real-time filter capable of monitoring network traffic down to the port level for unusual dynamics and changes in business as usual. This is accomplished in an unsupervised fashion without a priori knowledge of abnormal characteristics. Two novel methods for converting streaming binary data into a form amenable to graphics based search and change detection are introduced. These techniques are then successfully applied to 1999 KDD Cup network attack data log-on sessions to demonstrate that Data Modeling can detect attacks without prior training on any form of attack behavior. Finally, two new methods for data encryption using these ideas are proposed.

  3. Ablative Thermal Protection: An Overview

    NASA Technical Reports Server (NTRS)

    Laub, Bernie

    2003-01-01

    Contents include the following: Why ablative thermal protections - TPS. Ablative TPS chronology: strategic reentry systems, solid rocket motor nozzles, space (manned missions and planetary entry probes). Ablation mechanisms. Ablation material testing. Ablative material testing.

  4. Conditional ablation of TGF-β signaling inhibits tumor progression and invasion in an induced mouse bladder cancer model

    PubMed Central

    Liang, Yu; Zhu, Fengyu; Zhang, Haojie; Chen, Demeng; Zhang, Xiuhong; Gao, Qian; Li, Yang

    2016-01-01

    The role of transforming growth factor-β (TGF-β) signaling in cancer progression is still under debate. To determine the function of TGF-β signaling in bladder cancer progression, we conditionally knocked out the Tgfbr2 in mouse model after a N-butyl-N-4-hydroxybutyl Nitrosamine induced bladder carcinogenesis. We found the ablation of TGF-β signaling could inhibit the cancer cell proliferation, cancer stem cell population and EMT, hence suppressed the invasive cancer progression, which is similar with the result of TGF-β receptor I inhibitor treatment. These findings recognize the roles and mechanisms of TGF-β signaling in bladder cancer progression in vivo for the first time. PMID:27378170

  5. Laser ablation plume thermalization dynamics in background gases: Combined imaging, optical absorption and emission spectroscopy, and ion probe measurements

    SciTech Connect

    Geohegan, D.B.; Puretzky, A.A. |

    1995-02-01

    Combined diagnostic measurements are employed to characterize the penetration of energetic ablation plumes through background gases during a key transitional regime in which the ion flux is observed to split into distinct fast and slowed components. This apparently general phenomenon occurs over a limited range of distances at ambient pressures typically used for PLD (pulsed laser deposition) and may be important to film growth by PLD because a ``fast`` component of ions can arrive at the probe (or substrate) with little or no delay compared to propagation in vacuum. At longer distances, this ``fast`` component is completely attenuated, and only slowed distributions of ions are observed. Interestingly, this ``fast`` component is easily overlooked in imaging studies because the bright plume luminescence occurs in the slowed distribution. Time- and spatially-resolved optical absorption and emission spectroscopy are applied to experimentally determine the composition of the ``fast`` and ``slow`` propagating plume components for a single-component target ablation (yttrium) into an inert gas (argon) for correlation with quantitative imaging and ion probe measurements. The yttrium/argon system was chosen because optical absorption spectroscopy of both Y and Y+ was simultaneously possible and the inert nature of argon. Experimental results for several other systems, including Si/Ar, Si/He, YBCO/O{sub 2} are presented to illustrate variations in scattering mechanisms.

  6. COLD-SAT Dynamic Model Computer Code

    NASA Technical Reports Server (NTRS)

    Bollenbacher, G.; Adams, N. S.

    1995-01-01

    COLD-SAT Dynamic Model (CSDM) computer code implements six-degree-of-freedom, rigid-body mathematical model for simulation of spacecraft in orbit around Earth. Investigates flow dynamics and thermodynamics of subcritical cryogenic fluids in microgravity. Consists of three parts: translation model, rotation model, and slosh model. Written in FORTRAN 77.

  7. Effects of non-ablative fractional erbium glass laser treatment on gene regulation in human three-dimensional skin models.

    PubMed

    Amann, Philipp M; Marquardt, Yvonne; Steiner, Timm; Hölzle, Frank; Skazik-Voogt, Claudia; Heise, Ruth; Baron, Jens M

    2016-04-01

    Clinical experiences with non-ablative fractional erbium glass laser therapy have demonstrated promising results for dermal remodelling and for the indications of striae, surgical scars and acne scars. So far, molecular effects on human skin following treatment with these laser systems have not been elucidated. Our aim was to investigate laser-induced effects on skin morphology and to analyse molecular effects on gene regulation. Therefore, human three-dimensional (3D) organotypic skin models were irradiated with non-ablative fractional erbium glass laser systems enabling qRT-PCR, microarray and histological studies at same and different time points. A decreased mRNA expression of matrix metalloproteinases (MMPs) 3 and 9 was observed 3 days after treatment. MMP3 also remained downregulated on protein level, whereas the expression of other MMPs like MMP9 was recovered or even upregulated 5 days after irradiation. Inflammatory gene regulatory responses measured by the expression of chemokine (C-X-C motif) ligands (CXCL1, 2, 5, 6) and interleukin expression (IL8) were predominantly reduced. Epidermal differentiation markers such as loricrin, filaggrin-1 and filaggrin-2 were upregulated by both tested laser optics, indicating a potential epidermal involvement. These effects were also shown on protein level in the immunofluorescence analysis. This novel standardised laser-treated human 3D skin model proves useful for monitoring time-dependent ex vivo effects of various laser systems on gene expression and human skin morphology. Our study reveals erbium glass laser-induced regulations of MMP and interleukin expression. We speculate that these alterations on gene expression level could play a role for dermal remodelling, anti-inflammatory effects and increased epidermal differentiation. Our finding may have implications for further understanding of the molecular mechanism of erbium glass laser-induced effects on human skin.

  8. Dynamics of the standard model

    SciTech Connect

    Donoghue, J.F.; Golowich, E.; Holstein, B.R.

    1992-01-01

    Given the remarkable successes of the standard model, it is appropriate that books in the field no longer dwell on the development of our current understanding of high-energy physics but rather present the world as we now know it. Dynamics of the Standard Model by Donoghue, Golowich, and Holstein takes just this approach. Instead of showing the confusion of the 60s and 70s, the authors present the enlightenment of the 80s. They start by describing the basic features and structure of the standard model and then concentrate on the techniques whereby the model can be applied to the physical world, connecting the theory to the experimental results that are the source of its success. Because they do not dwell on ancient (pre-1980) history, the authors of this book are able to go into much more depth in describing how the model can be tied to experiment, and much of the information presented has been accessible previously only in journal articles in a highly technical form. Though all of the authors are card-carrying theorists they go out of their way to stress applications and phenomenology and to show the reader how real-life calculations of use to experimentalists are done and can be applied to physical situations: what assumptions are made in doing them and how well they work. This is of great value both to the experimentalist seeking a deeper understanding of how the standard model can be connected to data and to the theorist wanting to see how detailed the phenomenological predictions of the standard model are and how well the model works. Furthermore, the authors constantly go beyond the lowest-order predictions of the standard model to discuss the corrections to it, as well as higher-order processes, some of which are now experimentally accessible and others of which will take well into the decade to uncover.

  9. Characterizing and Modeling Citation Dynamics

    PubMed Central

    Eom, Young-Ho; Fortunato, Santo

    2011-01-01

    Citation distributions are crucial for the analysis and modeling of the activity of scientists. We investigated bibliometric data of papers published in journals of the American Physical Society, searching for the type of function which best describes the observed citation distributions. We used the goodness of fit with Kolmogorov-Smirnov statistics for three classes of functions: log-normal, simple power law and shifted power law. The shifted power law turns out to be the most reliable hypothesis for all citation networks we derived, which correspond to different time spans. We find that citation dynamics is characterized by bursts, usually occurring within a few years since publication of a paper, and the burst size spans several orders of magnitude. We also investigated the microscopic mechanisms for the evolution of citation networks, by proposing a linear preferential attachment with time dependent initial attractiveness. The model successfully reproduces the empirical citation distributions and accounts for the presence of citation bursts as well. PMID:21966387

  10. Dynamical modeling of tidal streams

    SciTech Connect

    Bovy, Jo

    2014-11-01

    I present a new framework for modeling the dynamics of tidal streams. The framework consists of simple models for the initial action-angle distribution of tidal debris, which can be straightforwardly evolved forward in time. Taking advantage of the essentially one-dimensional nature of tidal streams, the transformation to position-velocity coordinates can be linearized and interpolated near a small number of points along the stream, thus allowing for efficient computations of a stream's properties in observable quantities. I illustrate how to calculate the stream's average location (its 'track') in different coordinate systems, how to quickly estimate the dispersion around its track, and how to draw mock stream data. As a generative model, this framework allows one to compute the full probability distribution function and marginalize over or condition it on certain phase-space dimensions as well as convolve it with observational uncertainties. This will be instrumental in proper data analysis of stream data. In addition to providing a computationally efficient practical tool for modeling the dynamics of tidal streams, the action-angle nature of the framework helps elucidate how the observed width of the stream relates to the velocity dispersion or mass of the progenitor, and how the progenitors of 'orphan' streams could be located. The practical usefulness of the proposed framework crucially depends on the ability to calculate action-angle variables for any orbit in any gravitational potential. A novel method for calculating actions, frequencies, and angles in any static potential using a single orbit integration is described in the Appendix.

  11. Dynamical Modeling of Tidal Streams

    NASA Astrophysics Data System (ADS)

    Bovy, Jo

    2014-11-01

    I present a new framework for modeling the dynamics of tidal streams. The framework consists of simple models for the initial action-angle distribution of tidal debris, which can be straightforwardly evolved forward in time. Taking advantage of the essentially one-dimensional nature of tidal streams, the transformation to position-velocity coordinates can be linearized and interpolated near a small number of points along the stream, thus allowing for efficient computations of a stream's properties in observable quantities. I illustrate how to calculate the stream's average location (its "track") in different coordinate systems, how to quickly estimate the dispersion around its track, and how to draw mock stream data. As a generative model, this framework allows one to compute the full probability distribution function and marginalize over or condition it on certain phase-space dimensions as well as convolve it with observational uncertainties. This will be instrumental in proper data analysis of stream data. In addition to providing a computationally efficient practical tool for modeling the dynamics of tidal streams, the action-angle nature of the framework helps elucidate how the observed width of the stream relates to the velocity dispersion or mass of the progenitor, and how the progenitors of "orphan" streams could be located. The practical usefulness of the proposed framework crucially depends on the ability to calculate action-angle variables for any orbit in any gravitational potential. A novel method for calculating actions, frequencies, and angles in any static potential using a single orbit integration is described in the Appendix.

  12. Dynamically Evolving Models of Clusters

    NASA Astrophysics Data System (ADS)

    Bode, Paul W.; Berrington, Robert C.; Cohn, Haldan N.; Lugger, Phyllis M.

    1993-12-01

    An N-body method, with up to N=10(5) particles, is used to simulate the dynamical evolution of clusters of galaxies. Each galaxy is represented as an extended structure containing many particles, and the gravitational potential arises from the particles alone. The clusters initially contain 50 or 100 galaxies with masses distributed according to a Schechter function. Mass is apportioned between the galaxies and a smoothly distributed common group halo, or intra-cluster background. The fraction of the total cluster mass initially in this background is varied from 50% to 90%. The models begin in a virialized state. We will be presenting a videotape which contains animations of a number of these models. The animations show important physical processes, such as stripping, merging, and dynamical friction, as they take place, thus allowing one to observe the interplay of these processes in the global evolution of the system. When the galaxies have substantial dark halos (background mass fraction <=75%) a large, centrally located merger remnant is created. The galaxy number density profile around this dominant member becomes cusped, approaching an isothermal distribution. At the same time, the number of multiple nuclei increases. Comparing the 50-galaxy models to MKW/AWM clusters, the values of Delta M12 and the peculiar velocities of the first-ranked galaxies are best fit by a mix of model ages in the range 8--11 Gyr. The growth in luminosity of the first-ranked galaxy during this amount of time is consistent only with weak cannibalism.

  13. Ablation of sensory neurons in a genetic model of pancreatic ductal adenocarcinoma slows initiation and progression of cancer

    PubMed Central

    Saloman, Jami L.; Albers, Kathryn M.; Li, Dongjun; Hartman, Douglas J.; Crawford, Howard C.; Muha, Emily A.; Rhim, Andrew D.; Davis, Brian M.

    2016-01-01

    Pancreatic ductal adenocarcinoma (PDAC) is characterized by an exuberant inflammatory desmoplastic response. The PDAC microenvironment is complex, containing both pro- and antitumorigenic elements, and remains to be fully characterized. Here, we show that sensory neurons, an under-studied cohort of the pancreas tumor stroma, play a significant role in the initiation and progression of the early stages of PDAC. Using a well-established autochthonous model of PDAC (PKC), we show that inflammation and neuronal damage in the peripheral and central nervous system (CNS) occurs as early as the pancreatic intraepithelial neoplasia (PanIN) 2 stage. Also at the PanIN2 stage, pancreas acinar-derived cells frequently invade along sensory neurons into the spinal cord and migrate caudally to the lower thoracic and upper lumbar regions. Sensory neuron ablation by neonatal capsaicin injection prevented perineural invasion (PNI), astrocyte activation, and neuronal damage, suggesting that sensory neurons convey inflammatory signals from Kras-induced pancreatic neoplasia to the CNS. Neuron ablation in PKC mice also significantly delayed PanIN formation and ultimately prolonged survival compared with vehicle-treated controls (median survival, 7.8 vs. 4.5 mo; P = 0.001). These data establish a reciprocal signaling loop between the pancreas and nervous system, including the CNS, that supports inflammation associated with oncogenic Kras-induced neoplasia. Thus, pancreatic sensory neurons comprise an important stromal cell population that supports the initiation and progression of PDAC and may represent a potential target for prevention in high-risk populations. PMID:26929329

  14. Dynamical Modeling of Mars' Paleoclimate

    NASA Technical Reports Server (NTRS)

    Richardson, Mark I.

    2004-01-01

    This report summarizes work undertaken under a one-year grant from the NASA Mars Fundamental Research Program. The goal of the project was to initiate studies of the response of the Martian climate to changes in planetary obliquity and orbital elements. This work was undertaken with a three-dimensional numerical climate model based on the Geophysical Fluid Dynamics Laboratory (GFDL) Skyhi General Circulation Model (GCM). The Mars GCM code was adapted to simulate various obliquity and orbital parameter states. Using a version of the model with a basic water cycle (ice caps, vapor, and clouds), we examined changes in atmospheric water abundances and in the distribution of water ice sheets on the surface. This work resulted in a paper published in the Journal of Geophysical Research - Planets. In addition, the project saw the initial incorporation of a regolith water transport and storage scheme into the model. This scheme allows for interaction between water in the pores of the near subsurface (<3m) and the atmosphere. This work was not complete by the end of the one-year grant, but is now continuing within the auspices of a three-year grant of the same title awarded by the Mars Fundamental Research Program in late 2003.

  15. Quantification of the effect of electrical and thermal parameters on radiofrequency ablation for concentric tumour model of different sizes.

    PubMed

    Jamil, Muhammad; Ng, E Y K

    2015-07-01

    Radiofrequency ablation (RFA) has been increasingly used in treating cancer for multitude of situations in various tissue types. To perform the therapy safely and reliably, the effect of critical parameters needs to be known beforehand. Temperature plays an important role in the outcome of the therapy and any uncertainties in temperature assessment can be lethal. This study presents the RFA case of fixed tip temperature where we've analysed the effect of electrical conductivity, thermal conductivity and blood perfusion rate of the tumour and surrounding normal tissue on the radiofrequency ablation. Ablation volume was chosen as the characteristic to be optimised and temperature control was achieved via PID controller. The effect of all 6 parameters each having 3 levels was quantified with minimum number of experiments harnessing the fractional factorial characteristic of Taguchi's orthogonal arrays. It was observed that as the blood perfusion increases the ablation volume decreases. Increasing electrical conductivity of the tumour results in increase of ablation volume whereas increase in normal tissue conductivity tends to decrease the ablation volume and vice versa. Likewise, increasing thermal conductivity of the tumour results in enhanced ablation volume whereas an increase in thermal conductivity of the surrounding normal tissue has a debilitating effect on the ablation volume and vice versa. With increase in the size of the tumour (i.e., 2-3cm) the effect of each parameter is not linear. The parameter effect varies with change in size of the tumour that is manifested by the different gradient observed in ablation volume. Most important is the relative insensitivity of ablation volume to blood perfusion rate for smaller tumour size (2cm) that is also in accordance with the previous results presented in literature. These findings will provide initial insight for safe, reliable and improved treatment planning perceptively.

  16. Modeling sandhill crane population dynamics

    USGS Publications Warehouse

    Johnson, D.H.

    1979-01-01

    The impact of sport hunting on the Central Flyway population of sandhill cranes (Grus canadensis) has been a subject of controversy for several years. A recent study (Buller 1979) presented new and important information on sandhill crane population dynamics. The present report is intended to incorporate that and other information into a mathematical model for the purpose of assessing the long-range impact of hunting on the population of sandhill cranes.The model is a simple deterministic system that embodies density-dependent rates of survival and recruitment. The model employs four kinds of data: (1) spring population size of sandhill cranes, estimated from aerial surveys to be between 250,000 and 400,000 birds; (2) age composition in fall, estimated for 1974-76 to be 11.3% young; (3) annual harvest of cranes, estimated from a variety of sources to be about 5 to 7% of the spring population; and (4) age composition of harvested cranes, which was difficult to estimate but suggests that immatures were 2 to 4 times as vulnerable to hunting as adults.Because the true nature of sandhill crane population dynamics remains so poorly understood, it was necessary to try numerous (768 in all) combinations of survival and recruitment functions, and focus on the relatively few (37) that yielded population sizes and age structures comparable to those extant in the real population. Hunting was then applied to those simulated populations. In all combinations, hunting resulted in a lower asymptotic crane population, the decline ranging from 5 to 54%. The median decline was 22%, which suggests that a hunted sandhill crane population might be about three-fourths as large as it would be if left unhunted. Results apply to the aggregate of the three subspecies in the Central Flyway; individual subspecies or populations could be affected to a greater or lesser degree.

  17. MR monitoring of MR-guided radiofrequency thermal ablation of normal liver in an animal model.

    PubMed

    Boaz, T L; Lewin, J S; Chung, Y C; Duerk, J L; Clampitt, M E; Haaga, J R

    1998-01-01

    The purpose of this study was to determine the suitability of MRI to accurately detect radiofrequency (RF) thermoablative lesions created under MR guidance. In vivo RF lesions were created in the livers of six New Zealand White rabbits using a 2-mm-diameter titanium alloy RF electrode with a 20-mm exposed tip and a 50-W RF generator. This was performed using a 0.2T clinical C-arm MR imager for guidance and monitoring. Each animal was sacrificed and gross evaluation was performed. Histologic correlation was performed on the first two animals. The MR-compatible RF electrode was easily identified on rapid gradient-echo images used to guide electrode placement. A single lesion was created in each rabbit liver. Lesions ranged from approximately 10 to 17 mm in diameter (mean, 13.5 mm). T2-weighted and short T1 inversion recovery (STIR) images demonstrated lesions ranging in diameter from 12 to 18 mm (mean, 14.6 mm). Lesion dimensions determined from images closely correlated with those determined at gross examination with the discrepancy never exceeding 2 mm, for an r2 value of .87. MRI performed at the time of MR-guided RF ablation accurately demonstrated created lesions. This modality may provide a new option for the treatment of local and regional neoplastic disease. PMID:9500262

  18. Salivary Biomarkers Associated with Myocardial Necrosis: Results from an Alcohol Septal Ablation Model

    PubMed Central

    Foley, Joseph D.; Sneed, J. Darrell; Steinhubl, Steven R.; Kolasa, Justin R.; Ebersole, Jeffrey L.; Lin, Yushun; Kryscio, Richard J.; McDevitt, John T.; Campbell, Charles L.; Miller, Craig S.

    2013-01-01

    Objective To determine if salivary biomarkers demonstrate utility for identifying aspects of myocardial necrosis. Methods Twenty-one patients undergoing alcohol septal ablation (ASA) for treatment of hypertrophic cardiomyopathy provided serum and unstimulated whole saliva at baseline and incremental time points post-ASA. Samples were analyzed for seven biomarkers related to myocardial damage, inflammation and tissue remodeling using immunosorbent assays. Levels were compared to baseline and levels observed in 97 healthy controls. Results Biomarkers of myocardial damage and inflammation (i.e., troponin I, creatine kinase-MB, myoglobin, C-reactive protein) rose in serum 2 to 812-fold after ASA (p<0.01). Significant elevations of 2 to 3.5-fold were observed with C-reactive protein and troponin I in saliva (p<0.02). Significant correlations between levels in serum and saliva were observed for C-reactive protein, matrix metalloproteinase-9, and myeloperoxidase (p < 0.001). Conclusions Select salivary biomarkers reflect changes that occur during, and subsequent to, myocardial necrosis caused by ASA. PMID:23021916

  19. A simple model for flyer velocity from laser-induced forward transfer with a dynamic release layer

    NASA Astrophysics Data System (ADS)

    Shaw-Stewart, James; Lippert, Thomas; Nagel, Matthias; Nüesch, Frank; Wokaun, Alexander

    2012-09-01

    A simple 1-D model has been developed for the velocity of flyers in vacuum generated by laser-induced forward transfer (LIFT) with a dynamic release layer (DRL). It is an extension of a laser ablation model for metal flyer plates based on the Gurney model of explosive output for driving metal fragments. The model has been extended to the bilayer system of a DRL overlain with a transfer layer. The suitability of the model has been checked with experimental velocity data obtained from shadowgraphy. The experiments used bilayer samples of triazene polymer/aluminium, ablated from the backside through the substrate at reduced pressure (5 × 10-2 mbar). The results suggest that the Gurney energy approach provides the basis of a viable, physically relevant, algebraic model for LIFT, but other loss mechanisms still need be incorporated, particularly thermal loss into the fused silica substrate.

  20. Terminal Model Of Newtonian Dynamics

    NASA Technical Reports Server (NTRS)

    Zak, Michail

    1994-01-01

    Paper presents study of theory of Newtonian dynamics of terminal attractors and repellers, focusing on issues of reversibility vs. irreversibility and deterministic evolution vs. probabilistic or chaotic evolution of dynamic systems. Theory developed called "terminal dynamics" emphasizes difference between it and classical Newtonian dynamics. Also holds promise for explaining irreversibility, unpredictability, probabilistic behavior, and chaos in turbulent flows, in thermodynamic phenomena, and in other dynamic phenomena and systems.

  1. Floods and Societies: Dynamic Modeling

    NASA Astrophysics Data System (ADS)

    Di Baldassarre, G.; Viglione, A.; Carr, G.; Kuil, L., Jr.; Brandimarte, L.; Bloeschl, G.

    2014-12-01

    There is growing concern that future flood losses and fatalities might increase significantly in many regions of the world because of rapid urbanization in deltas and floodplains, in addition to sea level rise and climate change. To better anticipate long-term trajectories of future flood risk, there is a need to treat floodplains and deltas as fully coupled human-physical systems. Here we propose a novel approach to explore the long-term behavior emerging from the mutual interactions and feedbacks between physical and social systems. The implementation of our modeling framework shows that green societies, which cope with flooding by resettling out of floodplains, are more resilient to increasing flood frequency than technological societies, which deal with flooding by building levees. Also, we show that when coupled dynamics are accounted for, flood-poor periods could (paradoxically) be more dangerous than flood-rich periods.

  2. SSME structural dynamic model development

    NASA Technical Reports Server (NTRS)

    Foley, Michael J.

    1989-01-01

    The high pressure fuel turbopump (HPFTP) is a major component of the Space Shuttle Main Engine (SSME) powerhead. The device is a three stage centrifugal pump that is directly driven by a two stage hot gas turbine. The purpose of the pump is to deliver fuel (liquid hydrogen) from the low pressure fuel turbopump (LPFTP) through the main fuel valve (MFV) to the thrust chamber coolant circuits. In doing so, the pump pressurizes the fuel from an inlet pressure of approximately 178 psi to a discharge pressure of over 6000 psi. At full power level (FPL), the pump rotates at a speed of over 37,000 rpm while generating approximately 77,000 horsepower. Obviously, a pump failure at these speeds and power levels could jeopardize the mission. Results are summarized for work in which the solutions obtained from analytical models of the fuel turbopump impellers are compared with the results obtained from dynamic tests.

  3. Ablation of Martian glaciers

    NASA Technical Reports Server (NTRS)

    Moore, Henry J.; Davis, Philip A.

    1987-01-01

    Glacier like landforms are observed in the fretted terrain of Mars in the latitude belts near + or - 42 deg. It was suggested that sublimation or accumulation-ablation rates could be estimated for these glaciers if their shapes were known. To this end, photoclinometric profiles were obtained of a number of these landforms. On the basis of analyses of these profiles, it was concluded that ice is chiefly ablating from these landforms that either are inactive rock-glaciers or have materials within them that are moving exceedingly slowly at this time. These conclusions are consistent with other geologic information. The analyses were performed using a two-dimensional model of an isothermal glacier.

  4. Fast and automatic depth control of iterative bone ablation based on optical coherence tomography data

    NASA Astrophysics Data System (ADS)

    Fuchs, Alexander; Pengel, Steffen; Bergmeier, Jan; Kahrs, Lüder A.; Ortmaier, Tobias

    2015-07-01

    Laser surgery is an established clinical procedure in dental applications, soft tissue ablation, and ophthalmology. The presented experimental set-up for closed-loop control of laser bone ablation addresses a feedback system and enables safe ablation towards anatomical structures that usually would have high risk of damage. This study is based on combined working volumes of optical coherence tomography (OCT) and Er:YAG cutting laser. High level of automation in fast image data processing and tissue treatment enables reproducible results and shortens the time in the operating room. For registration of the two coordinate systems a cross-like incision is ablated with the Er:YAG laser and segmented with OCT in three distances. The resulting Er:YAG coordinate system is reconstructed. A parameter list defines multiple sets of laser parameters including discrete and specific ablation rates as ablation model. The control algorithm uses this model to plan corrective laser paths for each set of laser parameters and dynamically adapts the distance of the laser focus. With this iterative control cycle consisting of image processing, path planning, ablation, and moistening of tissue the target geometry and desired depth are approximated until no further corrective laser paths can be set. The achieved depth stays within the tolerances of the parameter set with the smallest ablation rate. Specimen trials with fresh porcine bone have been conducted to prove the functionality of the developed concept. Flat bottom surfaces and sharp edges of the outline without visual signs of thermal damage verify the feasibility of automated, OCT controlled laser bone ablation with minimal process time.

  5. A Fluorescence-Guided Laser Ablation System for Removal of Residual Cancer in a Mouse Model of Soft Tissue Sarcoma

    PubMed Central

    Lazarides, Alexander L.; Whitley, Melodi J.; Strasfeld, David B.; Cardona, Diana M.; Ferrer, Jorge M.; Mueller, Jenna L.; Fu, Henry L.; DeWitt, Suzanne Bartholf; Brigman, Brian E.; Ramanujam, Nimmi; Kirsch, David G.; Eward, William C.

    2016-01-01

    The treatment of soft tissue sarcoma (STS) generally involves tumor excision with a wide margin. Although advances in fluorescence imaging make real-time detection of cancer possible, removal is limited by the precision of the human eye and hand. Here, we describe a novel pulsed Nd:YAG laser ablation system that, when used in conjunction with a previously described molecular imaging system, can identify and ablate cancer in vivo. Mice with primary STS were injected with the protease-activatable probe LUM015 to label tumors. Resected tissues from the mice were then imaged and treated with the laser using the paired fluorescence-imaging/ laser ablation device, generating ablation clefts with sub-millimeter precision and minimal underlying tissue damage. Laser ablation was guided by fluorescence to target tumor tissues, avoiding normal structures. The selective ablation of tumor implants in vivo improved recurrence-free survival after tumor resection in a cohort of 14 mice compared to 12 mice that received no ablative therapy. This prototype system has the potential to be modified so that it can be used during surgery to improve recurrence-free survival in patients with cancer. PMID:26877775

  6. Radiative ablation of disks around massive stars

    NASA Astrophysics Data System (ADS)

    Kee, Nathaniel Dylan

    Hot, massive stars (spectral types O and B) have extreme luminosities (10. 4 -10. 6 L?) that drive strong stellar winds through UV line-scattering.Some massive stars also have disks, formed by either decretion from the star (as in the rapidly rotating "Classical Be stars"), or accretion during the star's formation. This dissertation examines the role of stellar radiation in driving (ablating) material away from these circumstellar disks. A key result is that the observed month to year decay of Classical Be disks can be explained by line-driven ablation without, as previously done, appealing to anomalously strong viscous diffusion. Moreover, the higher luminosity of O stars leads to ablation of optically thin disks on dynamical timescales of order a day, providing a natural explanation for the lack of observed Oe stars. In addition to the destruction of Be disks, this dissertation also introduces a model for their formation by coupling observationally inferred non-radial pulsation modes and rapid stellar rotation to launch material into orbiting Keplerian disks of Be-like densities. In contrast to such Be decretion disks, star-forming accretion disks are much denser and so are generally optically thick to continuum processes. To circumvent the computational challenges associated with radiation hydrodynamics through optically thick media, we develop an approximate method for treating continuum absorption in the limit of geometrically thin disks. The comparison of ablation with and without continuum absorption shows that accounting for disk optical thickness leads to less than a 50% reduction in ablation rate, implying that ablation rate depends mainly on stellar properties like luminosity. Finally, we discuss the role of "thin-shell mixing" in reducing X-rays from colliding wind binaries. Laminar, adiabatic shocks produce well understood X-ray emission, but the emission from radiatively cooled shocks is more complex due to thin-shell instabilities. The parameter

  7. Extension to Higher Mass Numbers of an Improved Knockout-Ablation-Coalescence Model for Secondary Neutron and Light Ion Production in Cosmic Ray Interactions

    NASA Astrophysics Data System (ADS)

    Indi Sriprisan, Sirikul; Townsend, Lawrence; Cucinotta, Francis A.; Miller, Thomas M.

    Purpose: An analytical knockout-ablation-coalescence model capable of making quantitative predictions of the neutron spectra from high-energy nucleon-nucleus and nucleus-nucleus collisions is being developed for use in space radiation protection studies. The FORTRAN computer code that implements this model is called UBERNSPEC. The knockout or abrasion stage of the model is based on Glauber multiple scattering theory. The ablation part of the model uses the classical evaporation model of Weisskopf-Ewing. In earlier work, the knockout-ablation model has been extended to incorporate important coalescence effects into the formalism. Recently, alpha coalescence has been incorporated, and the ability to predict light ion spectra with the coalescence model added. The earlier versions were limited to nuclei with mass numbers less than 69. In this work, the UBERNSPEC code has been extended to make predictions of secondary neutrons and light ion production from the interactions of heavy charged particles with higher mass numbers (as large as 238). The predictions are compared with published measurements of neutron spectra and light ion energy for a variety of collision pairs. Furthermore, the predicted spectra from this work are compared with the predictions from the recently-developed heavy ion event generator incorporated in the Monte Carlo radiation transport code HETC-HEDS.

  8. Photochemical ablation of organic solids

    NASA Astrophysics Data System (ADS)

    Yingling, Yaroslava G.; Garrison, Barbara J.

    2003-04-01

    We have investigated by molecular dynamics simulations the ablation of material that is onset by photochemical processes. We compare this system with only photochemical processes to a system containing photochemical and photothermal processes. The simulations reveal that ablation by purely photochemical processes is accompanied by the ejection of relatively cold massive molecular clusters from the surface of the sample. The top of the plume exhibits high temperatures whereas the residual part of the sample is cold. The removal of the damaged material through big molecular cluster ejection is consistent with experimental observations of low heat damage of material.

  9. Computational Modeling of Open-Irrigated Electrodes for Radiofrequency Cardiac Ablation Including Blood Motion-Saline Flow Interaction.

    PubMed

    González-Suárez, Ana; Berjano, Enrique; Guerra, Jose M; Gerardo-Giorda, Luca

    2016-01-01

    Radiofrequency catheter ablation (RFCA) is a routine treatment for cardiac arrhythmias. During RFCA, the electrode-tissue interface temperature should be kept below 80 °C to avoid thrombus formation. Open-irrigated electrodes facilitate power delivery while keeping low temperatures around the catheter. No computational model of an open-irrigated electrode in endocardial RFCA accounting for both the saline irrigation flow and the blood motion in the cardiac chamber has been proposed yet. We present the first computational model including both effects at once. The model has been validated against existing experimental results. Computational results showed that the surface lesion width and blood temperature are affected by both the electrode design and the irrigation flow rate. Smaller surface lesion widths and blood temperatures are obtained with higher irrigation flow rate, while the lesion depth is not affected by changing the irrigation flow rate. Larger lesions are obtained with increasing power and the electrode-tissue contact. Also, larger lesions are obtained when electrode is placed horizontally. Overall, the computational findings are in close agreement with previous experimental results providing an excellent tool for future catheter research.

  10. Computational Modeling of Open-Irrigated Electrodes for Radiofrequency Cardiac Ablation Including Blood Motion-Saline Flow Interaction

    PubMed Central

    González-Suárez, Ana; Berjano, Enrique; Guerra, Jose M.; Gerardo-Giorda, Luca

    2016-01-01

    Radiofrequency catheter ablation (RFCA) is a routine treatment for cardiac arrhythmias. During RFCA, the electrode-tissue interface temperature should be kept below 80°C to avoid thrombus formation. Open-irrigated electrodes facilitate power delivery while keeping low temperatures around the catheter. No computational model of an open-irrigated electrode in endocardial RFCA accounting for both the saline irrigation flow and the blood motion in the cardiac chamber has been proposed yet. We present the first computational model including both effects at once. The model has been validated against existing experimental results. Computational results showed that the surface lesion width and blood temperature are affected by both the electrode design and the irrigation flow rate. Smaller surface lesion widths and blood temperatures are obtained with higher irrigation flow rate, while the lesion depth is not affected by changing the irrigation flow rate. Larger lesions are obtained with increasing power and the electrode-tissue contact. Also, larger lesions are obtained when electrode is placed horizontally. Overall, the computational findings are in close agreement with previous experimental results providing an excellent tool for future catheter research. PMID:26938638

  11. Computational Modeling of Open-Irrigated Electrodes for Radiofrequency Cardiac Ablation Including Blood Motion-Saline Flow Interaction.

    PubMed

    González-Suárez, Ana; Berjano, Enrique; Guerra, Jose M; Gerardo-Giorda, Luca

    2016-01-01

    Radiofrequency catheter ablation (RFCA) is a routine treatment for cardiac arrhythmias. During RFCA, the electrode-tissue interface temperature should be kept below 80 °C to avoid thrombus formation. Open-irrigated electrodes facilitate power delivery while keeping low temperatures around the catheter. No computational model of an open-irrigated electrode in endocardial RFCA accounting for both the saline irrigation flow and the blood motion in the cardiac chamber has been proposed yet. We present the first computational model including both effects at once. The model has been validated against existing experimental results. Computational results showed that the surface lesion width and blood temperature are affected by both the electrode design and the irrigation flow rate. Smaller surface lesion widths and blood temperatures are obtained with higher irrigation flow rate, while the lesion depth is not affected by changing the irrigation flow rate. Larger lesions are obtained with increasing power and the electrode-tissue contact. Also, larger lesions are obtained when electrode is placed horizontally. Overall, the computational findings are in close agreement with previous experimental results providing an excellent tool for future catheter research. PMID:26938638

  12. Fragmentation and ablation during entry

    SciTech Connect

    Canavan, G.H.

    1997-09-01

    This note discusses objects that both fragment and ablate during entry, using the results of previous reports to describe the velocity, pressure, and fragmentation of entering objects. It shows that the mechanisms used there to describe the breakup of non-ablating objects during deceleration remain valid for most ablating objects. It treats coupled fragmentation and ablation during entry, building on earlier models that separately discuss the entry of objects that are hard, whose high heat of ablation permits little erosion, and those who are strong whose strength prevents fragmentation, which are discussed in ``Radiation from Hard Objects,`` ``Deceleration and Radiation of Strong, Hard, Asteroids During Atmospheric Impact,`` and ``Meteor Signature Interpretation.`` This note provides a more detailed treatment of the further breakup and separation of fragments during descent. It replaces the constraint on mass per unit area used earlier to determine the altitude and magnitude of peak power radiation with a detailed analytic solution of deceleration. Model predictions are shown to be in agreement with the key features of numerical calculations of deceleration. The model equations are solved for the altitudes of maximum radiation, which agree with numerical integrations. The model is inverted analytically to infer object size and speed from measurements of peak power and altitude to provide a complete model for the approximate inversion of meteor data.

  13. Effect of ambient gas pressure on pulsed laser ablation plume dynamics and ZnTe film growth

    SciTech Connect

    Rouleau, C.M.; Lowndes, D.H.; Geohegan, D.B.; Allard, L.F.; Strauss, M.A.; Cao, S.; Pedraza, A.J.; Puretzky, A.A.

    1995-12-01

    Epitaxial thin films of nitrogen-doped p-ZnTe were grown on single-crystal, semi-insulating Ga-As substrates via pulsed laser ablation of a stoichiometric ZnTe target. Both low pressure nitrogen ambients and high vacuum were used. Results of in situ reflection high energy electron diffraction (RHEED) and time-resolved ion probe measurements have been compared with ex situ Hall effect and transmission electron microscopy (TEM) measurements. A strong correlation was observed between the nature of the film`s surface during growth (2-D vs. 3-D, assessed via RHEED) and the ambient gas pressures employed during deposition. The extended defect content (assessed via cross-sectional TEM) in the region >150 mn from the film/substrate interface was found to increase with the ambient gas pressure during deposition, which could not be explained by lattice mismatch alone. At sufficiently high pressures, misoriented, columnar grains developed which were not only consistent with the RHEED observations but also were correlated with a marked decrease in Hall mobility and a slight decrease in hole concentration. Ion probe measurements, which monitored the attenuation and slowing of the ion current arriving at the substrate surface, indicated that for increasing nitrogen pressure the fast (vacuum) velocity distribution splits into a distinct fast and two collisionally-slowed components or modes. Gas controlled variations in these components mirrored trends in electrical properties and microstructural measurements.

  14. Dynamics of pulsed laser ablation plasmas in high-density CO2 near the critical point investigated by time-resolved shadowgraph imaging

    NASA Astrophysics Data System (ADS)

    Urabe, Keiichiro; Kato, Toru; Himeno, Shohei; Kato, Satoshi; Stauss, Sven; Baba, Motoyoshi; Suemoto, Tohru; Terashima, Kazuo

    2013-09-01

    Pulsed laser ablation (PLA) plasmas generated in high-density gases and liquids are promising for the synthesis of nanomaterials. However, the characteristics of such plasmas are still not well understood. In order to improve the understandings of PLA plasmas in high-density fluids including gases, liquids, and supercritical fluids (SCFs), we have investigated the dynamics of PLA plasmas in high-density carbon dioxide (CO2) . We report on experimental results of time-resolved shadowgraph imaging, from the generation of plasma plume to the extinction of cavitation bubbles. Shadowgraph images revealed that the PLA plasma dynamics showed two distinct behaviors. These are divided by gas-liquid coexistence curve and the so-called Widom line, which separates gas-like and liquid-like SCF domains. Furthermore, cavitation bubble observed in liquid CO2 near the critical point showed peculiar characteristics, the formation of an inner bubble and an outer shell structure, which so far has never been reported. The experiments indicate that thermophysical properties of PLA plasmas can be tuned by controlling solvent temperature and pressure around the critical point, which may be useful for materials processing. This work was supported financially in part by a Grant-in-Aid for Scientific Research on Innovative Areas (No. 21110002) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.

  15. Validating equation of state models in the ablative Richtmyer-Meshkov regime for indirect-drive inertial confinement fusion capsules

    NASA Astrophysics Data System (ADS)

    Loomis, Eric; Braun, Dave; Batha, Steve; Sorce, Charles; Landen, Otto

    2011-10-01

    Recent simulations have shown that isolated features on the outer surface of Inertial Confinement Fusion (ICF) ignition capsules can profoundly impact capsule performance by leading to mixing in the hotspot. Controlling the growth of these artifacts is complicated due to uncertainties in equation of state (EOS) models used in simulation codes. Here we report on measurements pertaining to the growth of isolated defects due to ablative Richtmyer-Meshkov in CH capsules in order to validate these models. Face-on transmission radiography was used to measure the evolution of Gaussian bump arrays in plastic targets. Au halfraums heated to radiation temperatures near 70 eV using 15 beams in a 5 ns pulse from the Omega laser (Laboratory for Laser Energetics, University of Rochester, NY) indirectly drove the samples. Shock speed measurements made with Omega's Active Shock BreakOut (ASBO) diagnostic in conjunction with the x-ray flux recorded by a soft x-ray power diagnostic (DANTE) were used to determine drive conditions in the target. These measurements show that SESAME 7592 is in closer agreement with shock speed and bump growth data compared to LEOS 5310.

  16. UV-laser ablation of ionic liquid matrices.

    PubMed

    Hellwig, Nils; Thrun, Alexander; Muskat, Tassilo; Grotemeyer, Jürgen

    2009-12-01

    Ionic liquid matrices are a new class of matrices used in MALDI mass spectrometry. The ablation process of several ionic liquid matrices was studied by determining the velocity distribution of ablated neutral matrix molecules. This was done by a postionization approach, where the neutrals were ionized in the ablation plume by a second laser pulse. It was found that a second, time-delayed ablation event occurs consisting completely of neutral molecules. To explain this, the reflected-shockwave model is used, which assumes that the shockwave emerging from the laser ablation is reflected at the sample holder surface. When the shockwave arrives at the sample surface it causes a second ablation.

  17. Fibre optic sensors for temperature and pressure monitoring in laser ablation: experiments on ex-vivo animal model

    NASA Astrophysics Data System (ADS)

    Tosi, Daniele; Saccomandi, Paola; Schena, Emiliano; Duraibabu, Dinesh B.; Poeggel, Sven; Adilzhan, Abzal; Aliakhmet, Kamilla; Silvestri, Sergio; Leen, Gabriel; Lewis, Elfed

    2016-05-01

    Optical fibre sensors have been applied to perform biophysical measurement in ex-vivo laser ablation (LA), on pancreas animal phantom. Experiments have been performed using Fibre Bragg Grating (FBG) arrays for spatially resolved temperature detection, and an all-glass Extrinsic Fabry-Perot Interferometer (EFPI) for pressure measurement. Results using a Nd:YAG laser source as ablation device, are presented and discussed.

  18. A reexamination of the abrasion-ablation model for the description of the nuclear fragmentation reaction

    NASA Astrophysics Data System (ADS)

    Gaimard, J.-J.; Schmidt, K.-H.

    1991-09-01

    The nuclear fragmentation reaction is studied as an important production mechanism for secondary beams. The geometrical abrasion model and a macroscopic evaporation model which describe the two steps of the reaction are reexamined. Several improvements and modifications of these models are discussed and a new model description incorporating these elements is proposed. In particular, the excitation energy and the angular-momentum distribution of the prefragments, the formulation of evaporation as a diffusion process and the role of microscopic structure in the production cross section are considered. The new model description preserves the simplicity and the transparency of the original models. The prediction of the new model are compared to those of the original models and to experimental cross sections. While the original models showed several systematic discrepancies in comparison to measured cross sections, the new model is able to reproduce the whole body of experimental data with satisfactory agreement.

  19. Modeling population dynamics: A quantile approach.

    PubMed

    Chavas, Jean-Paul

    2015-04-01

    The paper investigates the modeling of population dynamics, both conceptually and empirically. It presents a reduced form representation that provides a flexible characterization of population dynamics. It leads to the specification of a threshold quantile autoregression (TQAR) model, which captures nonlinear dynamics by allowing lag effects to vary across quantiles of the distribution as well as with previous population levels. The usefulness of the model is illustrated in an application to the dynamics of lynx population. We find statistical evidence that the quantile autoregression parameters vary across quantiles (thus rejecting the AR model as well as the TAR model) as well as with past populations (thus rejecting the quantile autoregression QAR model). The results document the nature of dynamics and cycle in the lynx population over time. They show how both the period of the cycle and the speed of population adjustment vary with population level and environmental conditions. PMID:25661501

  20. 1D modelling of nanosecond laser ablation of copper samples in argon at P = 1 atm with a wavelength of 532 nm

    NASA Astrophysics Data System (ADS)

    Clair, Guillaume; L'Hermite, Daniel

    2011-10-01

    A one-dimensional model is developed for nanosecond laser ablation of a metal target (Cu) in a background gas (Ar) at any pressure. Simulations are performed with a 6 ns FWHM Gaussian laser pulse at 532 nm with a fluence of 11.3 J.cm-2. Heating, melting, evaporation, and condensation are considered to model the laser-target interaction. Expansion of the plume is investigated solving the Euler equations in a lagrangian formalism. Plasma formation is taken into account by computing the ionic species densities up to the second order of ionization in both the ablated material and the background gas. Such formation implies a strong laser-plasma interaction, assuming that the absorption phenomena are photoionization, electron-atom, and electron-ion inverse Bremsstrahlung. Radiative losses are supposed to be only described by electron-ion Bremsstrahlung. Preliminary results are presented and discussed.

  1. Multidimensional Langevin Modeling of Nonoverdamped Dynamics

    NASA Astrophysics Data System (ADS)

    Schaudinnus, Norbert; Bastian, Björn; Hegger, Rainer; Stock, Gerhard

    2015-07-01

    Based on a given time series, data-driven Langevin modeling aims to construct a low-dimensional dynamical model of the underlying system. When dealing with physical data as provided by, e.g., all-atom molecular dynamics simulations, effects due to small damping may be important to correctly describe the statistics (e.g., the energy landscape) and the dynamics (e.g., transition times). To include these effects in a dynamical model, an algorithm that propagates a second-order Langevin scheme is derived, which facilitates the treatment of multidimensional data. Adopting extensive molecular dynamics simulations of a peptide helix, a five-dimensional model is constructed that successfully forecasts the complex structural dynamics of the system. Neglect of small damping effects, on the other hand, is shown to lead to significant errors and inconsistencies.

  2. System Dynamics Models and Institutional Pricing Decisions.

    ERIC Educational Resources Information Center

    Chen, Fiona

    1986-01-01

    A system dynamics model for the pricing of tuition is presented, illustrating how such models enable decision-makers to anticipate cause-and-effect relationships and test alternative courses of action. (Author)

  3. Preliminary shuttle structural dynamics modeling design study

    NASA Technical Reports Server (NTRS)

    1972-01-01

    The design and development of a structural dynamics model of the space shuttle are discussed. The model provides for early study of structural dynamics problems, permits evaluation of the accuracy of the structural and hydroelastic analysis methods used on test vehicles, and provides for efficiently evaluating potential cost savings in structural dynamic testing techniques. The discussion is developed around the modes in which major input forces and responses occur and the significant structural details in these modes.

  4. Using an Ablation Gradient Model to Characterize Annual Glacial Melt Contribution to Major Rivers in High Asia

    NASA Astrophysics Data System (ADS)

    Brodzik, M. J.; Armstrong, R. L.; Khalsa, S. J. S.; Painter, T. H.; Racoviteanu, A.; Rittger, K.

    2014-12-01

    Ice melt from mountain glaciers can represent a significant contribution to freshwater hydrological budgets, along with seasonal snow melt, rainfall and groundwater. In the rivers of High Asia, understanding the proportion of glacier ice melt is critical for water resource management of irrigation and planning for hydropower generation and human consumption. Current climate conditions are producing heterogeneous glacier responses across the Hindu Kush-Karakoram-Himalayan ranges. However, it is not yet clear how contrasting glacier patterns affect regional water resources. For example, in the Upper Indus basin, estimates of glacial contribution to runoff are often not distinguished from seasonal snow contribution, and vary widely, from as little as 15% to as much as 55%. While many studies are based on reasonable concepts, most are based on assumptions uninformed by actual snow or ice cover measurements. While straightforward temperature index models have been used to estimate glacier runoff in some Himalayan basins, application of these models in larger Himalayan basins is limited by difficulties in estimating key model parameters, particularly air temperature. Estimating glacial area from the MODIS Permanent Snow and Ice Extent (MODICE) product for the years 2000-2013, with recently released Shuttle Radar Topography Mission (SRTMGL3) elevation data, we use a simple ablation gradient approach to calculate an upper limit on the contribution of clean glacier ice melt to streamflow data. We present model results for the five major rivers with glaciated headwaters in High Asia: the Bramaputra, Ganges, Indus, Amu Darya and Syr Darya. Using GRDC historical discharge records, we characterize the annual contribution from glacier ice melt. We use MODICE interannual trends in each basin to estimate glacier ice melt uncertainties. Our results are being used in the USAID project, Contribution to High Asia Runoff from Ice and Snow (CHARIS), to inform regional-scale planning for

  5. The Challenges to Coupling Dynamic Geospatial Models

    SciTech Connect

    Goldstein, N

    2006-06-23

    Many applications of modeling spatial dynamic systems focus on a single system and a single process, ignoring the geographic and systemic context of the processes being modeled. A solution to this problem is the coupled modeling of spatial dynamic systems. Coupled modeling is challenging for both technical reasons, as well as conceptual reasons. This paper explores the benefits and challenges to coupling or linking spatial dynamic models, from loose coupling, where information transfer between models is done by hand, to tight coupling, where two (or more) models are merged as one. To illustrate the challenges, a coupled model of Urbanization and Wildfire Risk is presented. This model, called Vesta, was applied to the Santa Barbara, California region (using real geospatial data), where Urbanization and Wildfires occur and recur, respectively. The preliminary results of the model coupling illustrate that coupled modeling can lead to insight into the consequences of processes acting on their own.

  6. Comparative dynamics in a health investment model.

    PubMed

    Eisenring, C

    1999-10-01

    The method of comparative dynamics fully exploits the inter-temporal structure of optimal control models. I derive comparative dynamic results in a simplified demand for health model. The effect of a change in the depreciation rate on the optimal paths for health capital and investment in health is studied by use of a phase diagram.

  7. Hydration dynamics near a model protein surface

    SciTech Connect

    Russo, Daniela; Hura, Greg; Head-Gordon, Teresa

    2003-09-01

    The evolution of water dynamics from dilute to very high concentration solutions of a prototypical hydrophobic amino acid with its polar backbone, N-acetyl-leucine-methylamide (NALMA), is studied by quasi-elastic neutron scattering and molecular dynamics simulation for both the completely deuterated and completely hydrogenated leucine monomer. We observe several unexpected features in the dynamics of these biological solutions under ambient conditions. The NALMA dynamics shows evidence of de Gennes narrowing, an indication of coherent long timescale structural relaxation dynamics. The translational water dynamics are analyzed in a first approximation with a jump diffusion model. At the highest solute concentrations, the hydration water dynamics is significantly suppressed and characterized by a long residential time and a slow diffusion coefficient. The analysis of the more dilute concentration solutions takes into account the results of the 2.0M solution as a model of the first hydration shell. Subtracting the first hydration layer based on the 2.0M spectra, the translational diffusion dynamics is still suppressed, although the rotational relaxation time and residential time are converged to bulk-water values. Molecular dynamics analysis shows spatially heterogeneous dynamics at high concentration that becomes homogeneous at more dilute concentrations. We discuss the hydration dynamics results of this model protein system in the context of glassy systems, protein function, and protein-protein interfaces.

  8. Benchmarking of Planning Models Using Recorded Dynamics

    SciTech Connect

    Huang, Zhenyu; Yang, Bo; Kosterev, Dmitry

    2009-03-15

    Power system planning extensively uses model simulation to understand the dynamic behaviors and determine the operating limits of a power system. Model quality is key to the safety and reliability of electricity delivery. Planning model benchmarking, or model validation, has been one of the central topics in power engineering studies for years. As model validation aims at obtaining reasonable models to represent dynamic behavior of power system components, it has been essential to validate models against actual measurements. The development of phasor technology provides such measurements and represents a new opportunity for model validation as phasor measurements can capture power system dynamics with high-speed, time-synchronized data. Previously, methods for rigorous comparison of model simulation and recorded dynamics have been developed and applied to quantify model quality of power plants in the Western Electricity Coordinating Council (WECC). These methods can locate model components which need improvement. Recent work continues this effort and focuses on how model parameters may be calibrated to match recorded dynamics after the problematic model components are identified. A calibration method using Extended Kalman Filter technique is being developed. This paper provides an overview of prior work on model validation and presents new development on the calibration method and initial results of model parameter calibration.

  9. A Separable Model for Dynamic Networks

    PubMed Central

    Krivitsky, Pavel N.; Handcock, Mark S.

    2013-01-01

    Summary Models of dynamic networks — networks that evolve over time — have manifold applications. We develop a discrete-time generative model for social network evolution that inherits the richness and flexibility of the class of exponential-family random graph models. The model — a Separable Temporal ERGM (STERGM) — facilitates separable modeling of the tie duration distributions and the structural dynamics of tie formation. We develop likelihood-based inference for the model, and provide computational algorithms for maximum likelihood estimation. We illustrate the interpretability of the model in analyzing a longitudinal network of friendship ties within a school. PMID:24443639

  10. Launch Vehicle Dynamics Demonstrator Model

    NASA Technical Reports Server (NTRS)

    1963-01-01

    The effect of vibration on launch vehicle dynamics was studied. Conditions included three modes of instability. The film includes close up views of the simulator fuel tank with and without stability control.

  11. Map-based models in neuronal dynamics

    NASA Astrophysics Data System (ADS)

    Ibarz, B.; Casado, J. M.; Sanjuán, M. A. F.

    2011-04-01

    Ever since the pioneering work of Hodgkin and Huxley, biological neuron models have consisted of ODEs representing the evolution of the transmembrane voltage and the dynamics of ionic conductances. It is only recently that discrete dynamical systems-also known as maps-have begun to receive attention as valid phenomenological neuron models. The present review tries to provide a coherent perspective of map-based biological neuron models, describing their dynamical properties; stressing the similarities and differences, both among them and in relation to continuous-time models; exploring their behavior in networks; and examining their wide-ranging possibilities of application in computational neuroscience.

  12. [Review of dynamic global vegetation models (DGVMs)].

    PubMed

    Che, Ming-Liang; Chen, Bao-Zhang; Wang, Ying; Guo, Xiang-Yun

    2014-01-01

    Dynamic global vegetation model (DGVM) is an important and efficient tool for study on the terrestrial carbon circle processes and vegetation dynamics. This paper reviewed the development history of DGVMs, introduced the basic structure of DGVMs, and the outlines of several world-widely used DGVMs, including CLM-DGVM, LPJ, IBIS and SEIB. The shortages of the description of dynamic vegetation mechanisms in the current DGVMs were proposed, including plant functional types (PFT) scheme, vegetation competition, disturbance, and phenology. Then the future research directions of DGVMs were pointed out, i. e. improving the PFT scheme, refining the vegetation dynamic mechanism, and implementing a model inter-comparison project. PMID:24765870

  13. Early snowmelt decreases ablation period carbon uptake in a high elevation, subalpine forest, Niwot Ridge, Colorado, USA

    NASA Astrophysics Data System (ADS)

    Winchell, T. S.; Molotch, N. P.; Barnard, D. M.

    2015-12-01

    The snow ablation period is a time of great potential for carbon uptake in high-elevation, subalpine forests. During this period, water availability associated with snowmelt promotes photosynthetic carbon uptake, while snow cover diminishes carbon losses from soil respiration. Although the ablation period can be as short as two weeks, as much as 30% of the total seasonal carbon uptake can occur during this period. Varying ablation period dynamics, however, can result in varying rates of carbon uptake during this integral uptake period. We use fifteen years of observational climate flux and snow water equivalent (SWE) data for a subalpine forest in the Colorado Rocky Mountains to analyze carbon uptake trends during the annual ablation period. Specifically, we focus on how the timing of peak SWE affects carbon uptake during the ablation period. We find that when the snowmelt period occurs one month earlier than average, the forest experiences an ablation period mean air temperature of 2.7° C, approximately 5° C colder than an ablation period that occurs one month later than average. This early, colder atmospheric condition leads to daytime carbon uptake rates that are 2.5 gC/m2/day less than the later, warmer period, which results in 47 gC/m2 less ablation period carbon uptake. As most climate models project peak SWE to occur earlier under various warming scenarios, we can expect to see a trend of less carbon uptake during future ablation periods. We expect to see a decrease in total growing season carbon uptake if the post-snowmelt period is unable to compensate for the decrease in ablation period carbon uptake.

  14. Enhanced coupling of optical energy during liquid-confined metal ablation

    SciTech Connect

    Kang, Hyun Wook; Welch, Ashley J.

    2015-10-21

    Liquid-confined laser ablation was investigated with various metals of indium, aluminum, and nickel. Ablation threshold and rate were characterized in terms of surface deformation, transient acoustic responses, and plasma emissions. The surface condition affected the degree of ablation dynamics due to variations in reflectance. The liquid confinement yielded up to an order of larger ablation crater along with stronger acoustic transients than dry ablation. Enhanced ablation performance resulted possibly from effective coupling of optical energy at the interface during explosive vaporization, plasma confinement, and cavitation. The deposition of a liquid layer can induce more efficient ablation for laser metal processing.

  15. Stirling Convertor System Dynamic Model Developed

    NASA Technical Reports Server (NTRS)

    Lewandowski, Edward J.; Regan, Timothy F.

    2005-01-01

    Free-piston Stirling convertors are being developed for potential use on NASA exploration missions. In support of this effort, the NASA Glenn Research Center has developed the Stirling convertor System Dynamic Model (SDM). The SDM models the Stirling cycle thermodynamics; heat flow; gas, mechanical, and mounting dynamics; the linear alternator; and the controller. The SDM s scope extends from the thermal energy input to thermal, mechanical, and electrical energy output, allowing one to study complex system interactions among subsystems. Thermal, mechanical, fluid, magnetic, and electrical subsystems can be studied in one model. The SDM is a nonlinear time-domain model containing sub-cycle dynamics, which simulates transient and dynamic phenomena that other models cannot. The entire range of convertor operation is modeled, from startup to full-power conditions.

  16. Modelling Information System Dynamics: A Perspective.

    ERIC Educational Resources Information Center

    Oswitch, Pauline

    1983-01-01

    Describes British Library's work on Systems Dynamics, a set of techniques for building simulation models based on analysis of information feedback loops. Highlights include macro-simulation modelling activities of social science disciplines, systems analyses and models of information retrieval processes and library services, policy models, and…

  17. A novel mouse model of tuberous sclerosis complex (TSC): eye-specific Tsc1-ablation disrupts visual-pathway development

    PubMed Central

    Jones, Iwan; Hägglund, Anna-Carin; Törnqvist, Gunilla; Nord, Christoffer; Ahlgren, Ulf; Carlsson, Leif

    2015-01-01

    ABSTRACT Tuberous sclerosis complex (TSC) is an autosomal dominant syndrome that is best characterised by neurodevelopmental deficits and the presence of benign tumours (called hamartomas) in affected organs. This multi-organ disorder results from inactivating point mutations in either the TSC1 or the TSC2 genes and consequent activation of the canonical mammalian target of rapamycin complex 1 signalling (mTORC1) pathway. Because lesions to the eye are central to TSC diagnosis, we report here the generation and characterisation of the first eye-specific TSC mouse model. We demonstrate that conditional ablation of Tsc1 in eye-committed progenitor cells leads to the accelerated differentiation and subsequent ectopic radial migration of retinal ganglion cells. This results in an increase in retinal ganglion cell apoptosis and consequent regionalised axonal loss within the optic nerve and topographical changes to the contra- and ipsilateral input within the dorsal lateral geniculate nucleus. Eyes from adult mice exhibit aberrant retinal architecture and display all the classic neuropathological hallmarks of TSC, including an increase in organ and cell size, ring heterotopias, hamartomas with retinal detachment, and lamination defects. Our results provide the first major insight into the molecular etiology of TSC within the developing eye and demonstrate a pivotal role for Tsc1 in regulating various aspects of visual-pathway development. Our novel mouse model therefore provides a valuable resource for future studies concerning the molecular mechanisms underlying TSC and also as a platform to evaluate new therapeutic approaches for the treatment of this multi-organ disorder. PMID:26449264

  18. A novel mouse model of tuberous sclerosis complex (TSC): eye-specific Tsc1-ablation disrupts visual-pathway development.

    PubMed

    Jones, Iwan; Hägglund, Anna-Carin; Törnqvist, Gunilla; Nord, Christoffer; Ahlgren, Ulf; Carlsson, Leif

    2015-12-01

    Tuberous sclerosis complex (TSC) is an autosomal dominant syndrome that is best characterised by neurodevelopmental deficits and the presence of benign tumours (called hamartomas) in affected organs. This multi-organ disorder results from inactivating point mutations in either the TSC1 or the TSC2 genes and consequent activation of the canonical mammalian target of rapamycin complex 1 signalling (mTORC1) pathway. Because lesions to the eye are central to TSC diagnosis, we report here the generation and characterisation of the first eye-specific TSC mouse model. We demonstrate that conditional ablation of Tsc1 in eye-committed progenitor cells leads to the accelerated differentiation and subsequent ectopic radial migration of retinal ganglion cells. This results in an increase in retinal ganglion cell apoptosis and consequent regionalised axonal loss within the optic nerve and topographical changes to the contra- and ipsilateral input within the dorsal lateral geniculate nucleus. Eyes from adult mice exhibit aberrant retinal architecture and display all the classic neuropathological hallmarks of TSC, including an increase in organ and cell size, ring heterotopias, hamartomas with retinal detachment, and lamination defects. Our results provide the first major insight into the molecular etiology of TSC within the developing eye and demonstrate a pivotal role for Tsc1 in regulating various aspects of visual-pathway development. Our novel mouse model therefore provides a valuable resource for future studies concerning the molecular mechanisms underlying TSC and also as a platform to evaluate new therapeutic approaches for the treatment of this multi-organ disorder.

  19. Modeling of ablation by photospallation using the computer program PUFF/DFRACT

    SciTech Connect

    Antoun, T.; Seaman, L.; Glinsky, M.E.

    1995-03-01

    In general, macroscopic material failure is a manifestation of irreversible changes at the microscopic level. Many tissues, which may appear to be macroscopically homogeneous, are, at a fundamental microscopic level, a composite material. For example, cornea is composed of a hyaluronic acid matrix in which layers of collagen fibers are overlaid in a crossing pattern. The points where the collagen fibers intersect are potential nucleation sites for microscopic defects, which under the action of tensile stress, nucleate, grow and coalesce to form macroscopic failure planes, or spall planes. Using a model based on microstructural evolution, this paper examines the failure process during photoablation. Specifically, the paper describes a physically motivated, micromechanical model based on the nucleation and growth of spherical voids. This model is then used to simulate photoablation of cornea. Potential for using this model to predict the stress wave and material damage measured by experiment is discussed.

  20. Very Large System Dynamics Models - Lessons Learned

    SciTech Connect

    Jacob J. Jacobson; Leonard Malczynski

    2008-10-01

    This paper provides lessons learned from developing several large system dynamics (SD) models. System dynamics modeling practice emphasize the need to keep models small so that they are manageable and understandable. This practice is generally reasonable and prudent; however, there are times that large SD models are necessary. This paper outlines two large SD projects that were done at two Department of Energy National Laboratories, the Idaho National Laboratory and Sandia National Laboratories. This paper summarizes the models and then discusses some of the valuable lessons learned during these two modeling efforts.

  1. Dynamical vegetation-atmosphere modelling of the boreal zone

    NASA Astrophysics Data System (ADS)

    Tang, Hui; Stordal, Frode; Berntsen, Terje K.; Bryn, Anders

    2016-04-01

    Vegetation interacts with climate on seasonal to inter-annual time scales through albedo, roughness, evapotranspiration, CO2 sequestration and by influencing snow accumulation and ablation. The Scandinavian mountains and high latitudes is a hot spot for land-atmosphere feedback, as the future's increased winter minimum temperature supports a boreal tree line advance, lowering the surface albedo. The northern ecosystem is dominated by mires, boreal forests and alpine heaths, in addition to agricultural land. Model studies have shown that vegetation-climate feedbacks are strong enough to lead to regime shifts in vegetation and local climate in boreal regions. Biogeophysical factors, such as albedo, the Bowen ratio, and surface roughness, are all involved in these feedbacks, and they are also altered by land use change such as reforestation. For calculations of the dynamical coupling between the atmosphere and the vegetation we have used the Earth System Model NorESM, which includes several advanced features in its land surface model (CLM4.5), such as the inclusion of the radiative forcing due to black carbon and dust deposit onto snow, improved representation of fire, permafrost and its hydrological impact, a new snow cover fraction parameterization reflecting the hysteresis in fractional snow cover for a given snow depth between accumulation and melt phases, as well as dynamic vegetation coupled with carbon-nitrogen cycles. These new features improve the representation of surface albedo feedback in Arctic. We have performed experiments with coupled as well fixed ocean for the current as a quadrupled atmospheric CO2 situation. This model configuration is used to study changes in vegetation in a high end radiative forcing case. It is contrasted with an experiment where vegetation dynamics is neglected. Changes in the features of the vegetation along with surface fluxes, albedo and atmospheric temperatures are analysed, with main emphasis on the boreal zone. In

  2. Comparing models of Red Knot population dynamics

    USGS Publications Warehouse

    McGowan, Conor

    2015-01-01

    Predictive population modeling contributes to our basic scientific understanding of population dynamics, but can also inform management decisions by evaluating alternative actions in virtual environments. Quantitative models mathematically reflect scientific hypotheses about how a system functions. In Delaware Bay, mid-Atlantic Coast, USA, to more effectively manage horseshoe crab (Limulus polyphemus) harvests and protect Red Knot (Calidris canutus rufa) populations, models are used to compare harvest actions and predict the impacts on crab and knot populations. Management has been chiefly driven by the core hypothesis that horseshoe crab egg abundance governs the survival and reproduction of migrating Red Knots that stopover in the Bay during spring migration. However, recently, hypotheses proposing that knot dynamics are governed by cyclical lemming dynamics garnered some support in data analyses. In this paper, I present alternative models of Red Knot population dynamics to reflect alternative hypotheses. Using 2 models with different lemming population cycle lengths and 2 models with different horseshoe crab effects, I project the knot population into the future under environmental stochasticity and parametric uncertainty with each model. I then compare each model's predictions to 10 yr of population monitoring from Delaware Bay. Using Bayes' theorem and model weight updating, models can accrue weight or support for one or another hypothesis of population dynamics. With 4 models of Red Knot population dynamics and only 10 yr of data, no hypothesis clearly predicted population count data better than another. The collapsed lemming cycle model performed best, accruing ~35% of the model weight, followed closely by the horseshoe crab egg abundance model, which accrued ~30% of the weight. The models that predicted no decline or stable populations (i.e. the 4-yr lemming cycle model and the weak horseshoe crab effect model) were the most weakly supported.

  3. Human systems dynamics: Toward a computational model

    NASA Astrophysics Data System (ADS)

    Eoyang, Glenda H.

    2012-09-01

    A robust and reliable computational model of complex human systems dynamics could support advancements in theory and practice for social systems at all levels, from intrapersonal experience to global politics and economics. Models of human interactions have evolved from traditional, Newtonian systems assumptions, which served a variety of practical and theoretical needs of the past. Another class of models has been inspired and informed by models and methods from nonlinear dynamics, chaos, and complexity science. None of the existing models, however, is able to represent the open, high dimension, and nonlinear self-organizing dynamics of social systems. An effective model will represent interactions at multiple levels to generate emergent patterns of social and political life of individuals and groups. Existing models and modeling methods are considered and assessed against characteristic pattern-forming processes in observed and experienced phenomena of human systems. A conceptual model, CDE Model, based on the conditions for self-organizing in human systems, is explored as an alternative to existing models and methods. While the new model overcomes the limitations of previous models, it also provides an explanatory base and foundation for prospective analysis to inform real-time meaning making and action taking in response to complex conditions in the real world. An invitation is extended to readers to engage in developing a computational model that incorporates the assumptions, meta-variables, and relationships of this open, high dimension, and nonlinear conceptual model of the complex dynamics of human systems.

  4. Pulsed laser ablation of binary semiconductors: mechanisms of vaporisation and cluster formation

    SciTech Connect

    Bulgakov, A V; Evtushenko, A B; Shukhov, Yu G; Ozerov, I; Marin, W

    2010-12-29

    Formation of small clusters during pulsed ablation of two binary semiconductors, zinc oxide and indium phosphide, in vacuum by UV, visible, and IR laser radiation is comparatively studied. The irradiation conditions favourable for generation of neutral and charged Zn{sub n}O{sub m} and In{sub n}P{sub m} clusters of different stoichiometry in the ablation products are found. The size and composition of the clusters, their expansion dynamics and reactivity are analysed by time-of-flight mass spectrometry. A particular attention is paid to the mechanisms of ZnO and InP ablation as a function of laser fluence, with the use of different ablation models. It is established that ZnO evapourates congruently in a wide range of irradiation conditions, while InP ablation leads to enrichment of the target surface with indium. It is shown that this radically different character of semiconductor ablation determines the composition of the nanostructures formed: zinc oxide clusters are mainly stoichiometric, whereas In{sub n}P{sub m} particles are significantly enriched with indium. (photonics and nanotechnology)

  5. Modeling microbial growth and dynamics.

    PubMed

    Esser, Daniel S; Leveau, Johan H J; Meyer, Katrin M

    2015-11-01

    Modeling has become an important tool for widening our understanding of microbial growth in the context of applied microbiology and related to such processes as safe food production, wastewater treatment, bioremediation, or microbe-mediated mining. Various modeling techniques, such as primary, secondary and tertiary mathematical models, phenomenological models, mechanistic or kinetic models, reactive transport models, Bayesian network models, artificial neural networks, as well as agent-, individual-, and particle-based models have been applied to model microbial growth and activity in many applied fields. In this mini-review, we summarize the basic concepts of these models using examples and applications from food safety and wastewater treatment systems. We further review recent developments in other applied fields focusing on models that explicitly include spatial relationships. Using these examples, we point out the conceptual similarities across fields of application and encourage the combined use of different modeling techniques in hybrid models as well as their cross-disciplinary exchange. For instance, pattern-oriented modeling has its origin in ecology but may be employed to parameterize microbial growth models when experimental data are scarce. Models could also be used as virtual laboratories to optimize experimental design analogous to the virtual ecologist approach. Future microbial growth models will likely become more complex to benefit from the rich toolbox that is now available to microbial growth modelers.

  6. Modeling microbial growth and dynamics.

    PubMed

    Esser, Daniel S; Leveau, Johan H J; Meyer, Katrin M

    2015-11-01

    Modeling has become an important tool for widening our understanding of microbial growth in the context of applied microbiology and related to such processes as safe food production, wastewater treatment, bioremediation, or microbe-mediated mining. Various modeling techniques, such as primary, secondary and tertiary mathematical models, phenomenological models, mechanistic or kinetic models, reactive transport models, Bayesian network models, artificial neural networks, as well as agent-, individual-, and particle-based models have been applied to model microbial growth and activity in many applied fields. In this mini-review, we summarize the basic concepts of these models using examples and applications from food safety and wastewater treatment systems. We further review recent developments in other applied fields focusing on models that explicitly include spatial relationships. Using these examples, we point out the conceptual similarities across fields of application and encourage the combined use of different modeling techniques in hybrid models as well as their cross-disciplinary exchange. For instance, pattern-oriented modeling has its origin in ecology but may be employed to parameterize microbial growth models when experimental data are scarce. Models could also be used as virtual laboratories to optimize experimental design analogous to the virtual ecologist approach. Future microbial growth models will likely become more complex to benefit from the rich toolbox that is now available to microbial growth modelers. PMID:26298697

  7. Numerical models of cell death in RF ablation with monopolar and bipolar probes

    NASA Astrophysics Data System (ADS)

    Bright, Benjamin M.; Pearce, John A.

    2013-02-01

    Radio frequency (RF) is used clinically to treat unresectible tumors. Finite element modeling has proven useful in treatment planning and applicator design. Typically isotherms in the middle 50s °C have been used as the parameter of assessment in these models. We compare and contrast isotherms for multiple known Arrhenius thermal damage predictors including collagen denaturation, vascular disruption, liver coagulation and cell death. Models for RITA probe geometries are included in the study. Comparison to isotherms is sensible when the activation time is held constant, but varies considerably when heating times vary. The purpose of this paper is to demonstrate the importance of looking at specific processes and keeping track of the methods used to derive the Arrhenius coefficients in order to study the extremely complex cell death processes due to thermal therapies.

  8. Dynamic phase transition in diluted Ising model

    NASA Astrophysics Data System (ADS)

    Chattopadhyay, Sourav; Gorai, Gopal; Santra, S. B.

    2015-06-01

    Dynamic phase transition in disordered Ising model in two dimensions has been studied in presence of external time dependent oscillating magnetic field applying Glauber Monte Carlo techniques. Dynamic phase transitions are identified estimating dynamic order parameter against temperature for different concentrations of disorder. For a given field strength and frequency for which there was no hysteresis, it is observed that disorder is able induce hysteresis in the system. Effect of increasing concentration of disorder on hysteresis loop area has also been studied.

  9. Differential equation models for sharp threshold dynamics.

    PubMed

    Schramm, Harrison C; Dimitrov, Nedialko B

    2014-01-01

    We develop an extension to differential equation models of dynamical systems to allow us to analyze probabilistic threshold dynamics that fundamentally and globally change system behavior. We apply our novel modeling approach to two cases of interest: a model of infectious disease modified for malware where a detection event drastically changes dynamics by introducing a new class in competition with the original infection; and the Lanchester model of armed conflict, where the loss of a key capability drastically changes the effectiveness of one of the sides. We derive and demonstrate a step-by-step, repeatable method for applying our novel modeling approach to an arbitrary system, and we compare the resulting differential equations to simulations of the system's random progression. Our work leads to a simple and easily implemented method for analyzing probabilistic threshold dynamics using differential equations. PMID:24184349

  10. Equivalent dynamic model of DEMES rotary joint

    NASA Astrophysics Data System (ADS)

    Zhao, Jianwen; Wang, Shu; Xing, Zhiguang; McCoul, David; Niu, Junyang; Huang, Bo; Liu, Liwu; Leng, Jinsong

    2016-07-01

    The dielectric elastomer minimum energy structure (DEMES) can realize large angular deformations by a small voltage-induced strain of the dielectric elastomer (DE), so it is a suitable candidate to make a rotary joint for a soft robot. Dynamic analysis is necessary for some applications, but the dynamic response of DEMESs is difficult to model because of the complicated morphology and viscoelasticity of the DE film. In this paper, a method composed of theoretical analysis and experimental measurement is presented to model the dynamic response of a DEMES rotary joint under an alternating voltage. Based on measurements of equivalent driving force and damping of the DEMES, the model can be derived. Some experiments were carried out to validate the equivalent dynamic model. The maximum angle error between model and experiment is greater than ten degrees, but it is acceptable to predict angular velocity of the DEMES, therefore, it can be applied in feedforward–feedback compound control.

  11. Differential equation models for sharp threshold dynamics.

    PubMed

    Schramm, Harrison C; Dimitrov, Nedialko B

    2014-01-01

    We develop an extension to differential equation models of dynamical systems to allow us to analyze probabilistic threshold dynamics that fundamentally and globally change system behavior. We apply our novel modeling approach to two cases of interest: a model of infectious disease modified for malware where a detection event drastically changes dynamics by introducing a new class in competition with the original infection; and the Lanchester model of armed conflict, where the loss of a key capability drastically changes the effectiveness of one of the sides. We derive and demonstrate a step-by-step, repeatable method for applying our novel modeling approach to an arbitrary system, and we compare the resulting differential equations to simulations of the system's random progression. Our work leads to a simple and easily implemented method for analyzing probabilistic threshold dynamics using differential equations.

  12. Dynamics Modelling of Biolistic Gene Guns

    SciTech Connect

    Zhang, M.; Tao, W.; Pianetta, P.A.

    2009-06-04

    The gene transfer process using biolistic gene guns is a highly dynamic process. To achieve good performance, the process needs to be well understood and controlled. Unfortunately, no dynamic model is available in the open literature for analysing and controlling the process. This paper proposes such a model. Relationships of the penetration depth with the helium pressure, the penetration depth with the acceleration distance, and the penetration depth with the micro-carrier radius are presented. Simulations have also been conducted. The results agree well with experimental results in the open literature. The contribution of this paper includes a dynamic model for improving and manipulating performance of the biolistic gene gun.

  13. Simple Dynamic Gasifier Model That Runs in Aspen Dynamics

    SciTech Connect

    Robinson, P.J.; Luyben, W.L.

    2008-10-15

    Gasification (or partial oxidation) is a vital component of 'clean coal' technology. Sulfur and nitrogen emissions can be reduced, overall energy efficiency is increased, and carbon dioxide recovery and sequestration are facilitated. Gasification units in an electric power generation plant produce a fuel for driving combustion turbines. Gasification units in a chemical plant generate gas, which can be used to produce a wide spectrum of chemical products. Future plants are predicted to be hybrid power/chemical plants with gasification as the key unit operation. The widely used process simulator Aspen Plus provides a library of models that can be used to develop an overall gasifier model that handles solids. So steady-state design and optimization studies of processes with gasifiers can be undertaken. This paper presents a simple approximate method for achieving the objective of having a gasifier model that can be exported into Aspen Dynamics. The basic idea is to use a high molecular weight hydrocarbon that is present in the Aspen library as a pseudofuel. This component should have the same 1:1 hydrogen-to-carbon ratio that is found in coal and biomass. For many plantwide dynamic studies, a rigorous high-fidelity dynamic model of the gasifier is not needed because its dynamics are very fast and the gasifier gas volume is a relatively small fraction of the total volume of the entire plant. The proposed approximate model captures the essential macroscale thermal, flow, composition, and pressure dynamics. This paper does not attempt to optimize the design or control of gasifiers but merely presents an idea of how to dynamically simulate coal gasification in an approximate way.

  14. Markov state models of biomolecular conformational dynamics

    PubMed Central

    Chodera, John D.; Noé, Frank

    2014-01-01

    It has recently become practical to construct Markov state models (MSMs) that reproduce the long-time statistical conformational dynamics of biomolecules using data from molecular dynamics simulations. MSMs can predict both stationary and kinetic quantities on long timescales (e.g. milliseconds) using a set of atomistic molecular dynamics simulations that are individually much shorter, thus addressing the well-known sampling problem in molecular dynamics simulation. In addition to providing predictive quantitative models, MSMs greatly facilitate both the extraction of insight into biomolecular mechanism (such as folding and functional dynamics) and quantitative comparison with single-molecule and ensemble kinetics experiments. A variety of methodological advances and software packages now bring the construction of these models closer to routine practice. Here, we review recent progress in this field, considering theoretical and methodological advances, new software tools, and recent applications of these approaches in several domains of biochemistry and biophysics, commenting on remaining challenges. PMID:24836551

  15. Effect of the thermal wave in radiofrequency ablation modeling: an analytical study.

    PubMed

    Molina, Juan A López; Rivera, Maria J; Trujillo, Macarena; Berjano, Enrique J

    2008-03-01

    To date, all radiofrequency heating (RFH) theoretical models have employed Fourier's heat transfer equation (FHTE), which assumes infinite thermal energy propagation speed. Although this equation is probably suitable for modeling most RFH techniques, it may not be so for surgical procedures in which very short heating times are employed. In such cases, a non-Fourier model should be considered by using the hyperbolic heat transfer equation (HHTE). Our aim was to compare the temperature profiles obtained from the FHTE and HHTE for RFH modeling. We built a one-dimensional theoretical model based on a spherical electrode totally embedded and in close contact with biological tissue of infinite dimensions. We solved the electrical-thermal coupled problem analytically by including the power source in both equations. A comparison of the analytical solutions from the HHTE and FHTE showed that (1) for short times and locations close to the electrode surface, the HHTE produced temperatures higher than the FHTE, however, this trend became negligible for longer times, when both equations produced similar temperature profiles (HHTE always being higher than FHTE); (2) for points distant from the electrode surface and for very short times, the HHTE temperature was lower than the FHTE, however, after a delay time, this tendency inverted and the HHTE temperature increased to the maximum; (3) from a mathematical point of view, the HHTE solution showed cuspidal-type singularities, which were materialized as a temperature peak traveling through the medium at a finite speed. This peak rose at the electrode surface, and clearly reflected the wave nature of the thermal problem; (4) the differences between the FHTE and HHTE temperature profiles were smaller for the lower values of thermal relaxation time and locations further from the electrode surface.

  16. Study of laser-plasma interaction using a physics-based model for understanding the physical mechanism of double-pulse effect in nanosecond laser ablation

    SciTech Connect

    Wu Benxin; Zhou Yun; Forsman, Andrew

    2009-12-21

    This paper studies the double-pulse effect in high-intensity ({>=}{approx}GW/cm{sup 2}) nanosecond (ns) laser ablation, which refers to the significant material removal rate enhancement for ablation by two ns laser pulses (often separated by a delay time of {approx}10 to 100 ns). The early-stage interaction of the second laser pulse with the plasma plume created by the first pulse is very important for understanding the physical mechanism of the double pulse effect. However, the plasma properties in the early stage (during a laser pulse or within 20 to 30 ns after the completion of the pulse) are very difficult to measure experimentally. In this letter, a physics-based predictive model is used as the investigation tool, which was previously verified based on experiments on plasma properties in the late stage, which are relatively easy to measure. The study shows that the second laser pulse does not directly strike the target condensed phase. Instead, it mainly interacts with the plasma plume created by the first laser pulse, heats and accelerates the ablated material in the plume lingering above the target surface.

  17. Preparation of liposomal amiodarone and investigation of its cardiomyocyte-targeting ability in cardiac radiofrequency ablation rat model.

    PubMed

    Zhuge, Ying; Zheng, Zhi-Feng; Xie, Mu-Qing; Li, Lin; Wang, Fang; Gao, Feng

    2016-01-01

    The objective of this study was to develop an amiodarone hydrochloride (ADHC)-loaded liposome (ADHC-L) formulation and investigate its potential for cardiomyocyte targeting after cardiac radiofrequency ablation (CA) in vivo. The ADHC-L was prepared by thin-film method combined with ultrasonication and extrusion. The preparation process was optimized by Box-Behnken design with encapsulation efficiency as the main evaluation index. The optimum formulation was quantitatively obtained with a diameter of 99.9±0.4 nm, a zeta potential of 35.1±10.9 mV, and an encapsulation efficiency of 99.5%±13.3%. Transmission electron microscopy showed that the liposomes were spherical particles with integrated bilayers and well dispersed with high colloidal stability. Pharmacokinetic studies were investigated in rats after intravenous administration, which revealed that compared with free ADHC treatment, ADHC-L treatment showed a 5.1-fold increase in the area under the plasma drug concentration-time curve over a period of 24 hours (AUC0-24 h) and an 8.5-fold increase in mean residence time, suggesting that ADHC-L could facilitate drug release in a more stable and sustained manner while increasing the circulation time of ADHC, especially in the blood. Biodistribution studies of ADHC-L demonstrated that ADHC concentration in the heart was 4.1 times higher after ADHC-L treatment in CA rat model compared with ADHC-L sham-operated treatment at 20 minutes postinjection. Fluorescence imaging studies further proved that the heart-targeting ability of ADHC-L was mainly due to the CA in rats. These results strongly support that ADHC-L could be exploited as a potential heart-targeting drug delivery system with enhanced bioavailability and reduced side effects for arrhythmia treatment after CA. PMID:27313453

  18. Preparation of liposomal amiodarone and investigation of its cardiomyocyte-targeting ability in cardiac radiofrequency ablation rat model

    PubMed Central

    Zhuge, Ying; Zheng, Zhi-Feng; Xie, Mu-Qing; Li, Lin; Wang, Fang; Gao, Feng

    2016-01-01

    The objective of this study was to develop an amiodarone hydrochloride (ADHC)-loaded liposome (ADHC-L) formulation and investigate its potential for cardiomyocyte targeting after cardiac radiofrequency ablation (CA) in vivo. The ADHC-L was prepared by thin-film method combined with ultrasonication and extrusion. The preparation process was optimized by Box–Behnken design with encapsulation efficiency as the main evaluation index. The optimum formulation was quantitatively obtained with a diameter of 99.9±0.4 nm, a zeta potential of 35.1±10.9 mV, and an encapsulation efficiency of 99.5%±13.3%. Transmission electron microscopy showed that the liposomes were spherical particles with integrated bilayers and well dispersed with high colloidal stability. Pharmacokinetic studies were investigated in rats after intravenous administration, which revealed that compared with free ADHC treatment, ADHC-L treatment showed a 5.1-fold increase in the area under the plasma drug concentration–time curve over a period of 24 hours (AUC0–24 h) and an 8.5-fold increase in mean residence time, suggesting that ADHC-L could facilitate drug release in a more stable and sustained manner while increasing the circulation time of ADHC, especially in the blood. Biodistribution studies of ADHC-L demonstrated that ADHC concentration in the heart was 4.1 times higher after ADHC-L treatment in CA rat model compared with ADHC-L sham-operated treatment at 20 minutes postinjection. Fluorescence imaging studies further proved that the heart-targeting ability of ADHC-L was mainly due to the CA in rats. These results strongly support that ADHC-L could be exploited as a potential heart-targeting drug delivery system with enhanced bioavailability and reduced side effects for arrhythmia treatment after CA. PMID:27313453

  19. Dynamic T{sub 2}-mapping during magnetic resonance guided high intensity focused ultrasound ablation of bone marrow

    SciTech Connect

    Waspe, Adam C.; Looi, Thomas; Mougenot, Charles; Amaral, Joao; Temple, Michael; Sivaloganathan, Siv; Drake, James M.

    2012-11-28

    Focal bone tumor treatments include amputation, limb-sparing surgical excision with bone reconstruction, and high-dose external-beam radiation therapy. Magnetic resonance guided high intensity focused ultrasound (MR-HIFU) is an effective non-invasive thermotherapy for palliative management of bone metastases pain. MR thermometry (MRT) measures the proton resonance frequency shift (PRFS) of water molecules and produces accurate (<1 Degree-Sign C) and dynamic (<5s) thermal maps in soft tissues. PRFS-MRT is ineffective in fatty tissues such as yellow bone marrow and, since accurate temperature measurements are required in the bone to ensure adequate thermal dose, MR-HIFU is not indicated for primary bone tumor treatments. Magnetic relaxation times are sensitive to lipid temperature and we hypothesize that bone marrow temperature can be determined accurately by measuring changes in T{sub 2}, since T{sub 2} increases linearly in fat during heating. T{sub 2}-mapping using dual echo times during a dynamic turbo spin-echo pulse sequence enabled rapid measurement of T{sub 2}. Calibration of T{sub 2}-based thermal maps involved heating the marrow in a bovine femur and simultaneously measuring T{sub 2} and temperature with a thermocouple. A positive T{sub 2} temperature dependence in bone marrow of 20 ms/ Degree-Sign C was observed. Dynamic T{sub 2}-mapping should enable accurate temperature monitoring during MR-HIFU treatment of bone marrow and shows promise for improving the safety and reducing the invasiveness of pediatric bone tumor treatments.

  20. Airship dynamics modeling: A literature review

    NASA Astrophysics Data System (ADS)

    Li, Yuwen; Nahon, Meyer; Sharf, Inna

    2011-04-01

    The resurgence of airships has created a need for dynamics models and simulation capabilities adapted to these lighter-than-air vehicles. However, the modeling techniques for airship dynamics have lagged behind and are less systematic than those for fixed-wing aircraft. A state-of-the-art literature review is presented on airship dynamics modeling, aiming to provide a comprehensive description of the main problems in this area and a useful source of references for researchers and engineers interested in modern airship applications. The references are categorized according to the major topics in this area: aerodynamics, flight dynamics, incorporation of structural flexibility, incorporation of atmospheric turbulence, and effects of ballonets. Relevant analytical, numerical, and semi-empirical techniques are discussed, with a particular focus on how the main differences between lighter-than-air and heavier-than-air aircraft have been addressed in the modeling. Directions are suggested for future research on each of these topics.

  1. Constructing minimal models for complex system dynamics

    NASA Astrophysics Data System (ADS)

    Barzel, Baruch; Liu, Yang-Yu; Barabási, Albert-László

    2015-05-01

    One of the strengths of statistical physics is the ability to reduce macroscopic observations into microscopic models, offering a mechanistic description of a system's dynamics. This paradigm, rooted in Boltzmann's gas theory, has found applications from magnetic phenomena to subcellular processes and epidemic spreading. Yet, each of these advances were the result of decades of meticulous model building and validation, which are impossible to replicate in most complex biological, social or technological systems that lack accurate microscopic models. Here we develop a method to infer the microscopic dynamics of a complex system from observations of its response to external perturbations, allowing us to construct the most general class of nonlinear pairwise dynamics that are guaranteed to recover the observed behaviour. The result, which we test against both numerical and empirical data, is an effective dynamic model that can predict the system's behaviour and provide crucial insights into its inner workings.

  2. Automated adaptive inference of phenomenological dynamical models

    PubMed Central

    Daniels, Bryan C.; Nemenman, Ilya

    2015-01-01

    Dynamics of complex systems is often driven by large and intricate networks of microscopic interactions, whose sheer size obfuscates understanding. With limited experimental data, many parameters of such dynamics are unknown, and thus detailed, mechanistic models risk overfitting and making faulty predictions. At the other extreme, simple ad hoc models often miss defining features of the underlying systems. Here we develop an approach that instead constructs phenomenological, coarse-grained models of network dynamics that automatically adapt their complexity to the available data. Such adaptive models produce accurate predictions even when microscopic details are unknown. The approach is computationally tractable, even for a relatively large number of dynamical variables. Using simulated data, it correctly infers the phase space structure for planetary motion, avoids overfitting in a biological signalling system and produces accurate predictions for yeast glycolysis with tens of data points and over half of the interacting species unobserved. PMID:26293508

  3. The Higher Moments Dynamic on SIS Model

    NASA Astrophysics Data System (ADS)

    Pinto, Alberto; Martins, José; Stollenwerk, Nico

    2009-09-01

    The basic contact process or the SIS model is a well known epidemic process and have been studied for a wide class of people. In an epidemiological context, many authors worked on the SIS model considering only the dynamic of the first moments of infecteds, i.e., the mean value and the variance of the infected individuals. In this work, we study not only the dynamic of the first moments of infecteds but also on the dynamic of the higher moments. Recursively, we consider the dynamic equations for all the moments of infecteds and, applying the moment closure approximation, we obtain the stationary states of the state variables. We observe that the stationary states of the SIS model, in the moment closure approximation, can be used to obtain good approximations of the quasi-stationary states of the SIS model.

  4. MODELING MICROBUBBLE DYNAMICS IN BIOMEDICAL APPLICATIONS*

    PubMed Central

    CHAHINE, Georges L.; HSIAO, Chao-Tsung

    2012-01-01

    Controlling microbubble dynamics to produce desirable biomedical outcomes when and where necessary and avoid deleterious effects requires advanced knowledge, which can be achieved only through a combination of experimental and numerical/analytical techniques. The present communication presents a multi-physics approach to study the dynamics combining viscous- in-viscid effects, liquid and structure dynamics, and multi bubble interaction. While complex numerical tools are developed and used, the study aims at identifying the key parameters influencing the dynamics, which need to be included in simpler models. PMID:22833696

  5. Influence of water environment on holmium laser ablation performance for hard tissues.

    PubMed

    Lü, Tao; Xiao, Qing; Li, Zhengjia

    2012-05-01

    This study clarifies the ablation differences in air and in water for hard biological tissues, which are irradiated by fiber-guided long-pulsed holmium lasers. High-speed photography is used to record the dynamic characteristics of ablation plumes and vaporization bubbles induced by pulsed holmium lasers. The ablation morphologies and depth of hard tissues are quantitatively measured by optical coherence microscopy. Explosive vaporization effects in water play a positive role in the contact ablation process and are directly responsible for significant ablation enhancement. Furthermore, water layer depth can also contribute to ablation performance. Under the same laser parameters for fiber-tissue contact ablation in air and water, ablation performances are comparable for a single-laser pulse, but for more laser pulses the ablation performances in water are better than those in air. Comprehensive knowledge of ablation differences under various environments is important, especially in medical procedures that are performed in a liquid environment.

  6. A mouse model of spontaneous preterm birth based on the genetic ablation of biglycan and decorin.

    PubMed

    Calmus, Megan L; Macksoud, Elyse E; Tucker, Richard; Iozzo, Renato V; Lechner, Beatrice E

    2011-07-01

    Preterm premature rupture of membranes is responsible for one-third of preterm births. Ehlers-Danlos syndrome (EDS) is associated with preterm premature rupture of membranes in humans. In particular, an EDS variant is caused by a genetic mutation resulting in abnormal secretion of biglycan and decorin, two small leucine-rich proteoglycans highly expressed in reproductive tissues. Because biglycan/decorin null mutant (Bgn(-/-)Dcn(-/-)) mice demonstrate phenotypic changes similar to EDS, we used this model to test whether either biglycan or decorin or both play a role in the attainment of successful term gestation. Wild-type biglycan null mutant, decorin null mutant, and biglycan/decorin null mutant pregnancies were assessed for the length of gestation, pup and placenta weight, and litter size. Quantitative real-time PCR was performed to measure biglycan and decorin gene expression, and immunohistochemistry was performed to assess protein expression in placenta and fetal membranes at embryonic days E12, E15, and E18. Bgn(-/-)Dcn(-/-) dams displayed preterm birth, whereas the possession of at least two biglycan or decorin wild-type alleles was protective of preterm birth. The number of Bgn(-/-)Dcn(-/-) pups was decreased at postnatal day P1 but not at E18. Biglycan and decorin were upregulated in the placenta in the absence of each other and were developmentally regulated in fetal membranes, suggesting that these two proteoglycans demonstrate genetic complementation and contribute to gestational success in a dose-dependent manner. Thus, the biglycan/decorin null mutant mouse is a model of genetically induced preterm birth and perinatal loss. This model presents novel targets for preventive or therapeutic manipulation of preterm birth.

  7. Analytical model of the ablative Rayleigh-Taylor instability in the deceleration phase

    SciTech Connect

    Sanz, J.; Betti, R.

    2005-04-15

    A sharp boundary model for the deceleration phase of imploding capsules in inertial confinement fusion, in both direct and indirect drive, has been developed. The model includes heat conduction, local {alpha}-particle energy deposition, and shell compressibility effects. A differential equation for the temporal evolution of the modal amplitude interface is obtained. It is found that the {alpha}-particle energy has a strong influence on the evolution of the low l modes, via the compressibility of the shell. The modes are damped by vorticity convection, fire polishing, and {alpha}-particle energy deposition. The existence of a cutoff l number arises from the high blow of velocity into the hot region (rocket effect) if density gradient scale length effects are taken into account at the interface. The differential equation for the modal amplitude is used as a postprocessor to the results of 1D-SARA code [J. J. Honrubia, J. Quant. Spectrosc. Radiat. Transfer. 49, 491 (1993)] in a typical capsule for indirect-drive ignition designed on the National Ignition Facility. It is found that modes with l>180 are completely stabilized. The results are in agreement with two-dimensional simulations.

  8. Dynamic metabolic models in context: biomass backtracking.

    PubMed

    Tummler, Katja; Kühn, Clemens; Klipp, Edda

    2015-08-01

    Mathematical modeling has proven to be a powerful tool to understand and predict functional and regulatory properties of metabolic processes. High accuracy dynamic modeling of individual pathways is thereby opposed by simplified but genome scale constraint based approaches. A method that links these two powerful techniques would greatly enhance predictive power but is so far lacking. We present biomass backtracking, a workflow that integrates the cellular context in existing dynamic metabolic models via stoichiometrically exact drain reactions based on a genome scale metabolic model. With comprehensive examples, for different species and environmental contexts, we show the importance and scope of applications and highlight the improvement compared to common boundary formulations in existing metabolic models. Our method allows for the contextualization of dynamic metabolic models based on all available information. We anticipate this to greatly increase their accuracy and predictive power for basic research and also for drug development and industrial applications.

  9. Single timepoint models of dynamic systems.

    PubMed

    Sachs, K; Itani, S; Fitzgerald, J; Schoeberl, B; Nolan, G P; Tomlin, C J

    2013-08-01

    Many interesting studies aimed at elucidating the connectivity structure of biomolecular pathways make use of abundance measurements, and employ statistical and information theoretic approaches to assess connectivities. These studies often do not address the effects of the dynamics of the underlying biological system, yet dynamics give rise to impactful issues such as timepoint selection and its effect on structure recovery. In this work, we study conditions for reliable retrieval of the connectivity structure of a dynamic system, and the impact of dynamics on structure-learning efforts. We encounter an unexpected problem not previously described in elucidating connectivity structure from dynamic systems, show how this confounds structure learning of the system and discuss possible approaches to overcome the confounding effect. Finally, we test our hypotheses on an accurate dynamic model of the IGF signalling pathway. We use two structure-learning methods at four time points to contrast the performance and robustness of those methods in terms of recovering correct connectivity. PMID:24511382

  10. Thermal modeling for pulsed radiofrequency ablation: analytical study based on hyperbolic heat conduction.

    PubMed

    López Molina, Juan A; Rivera, María J; Trujillo, Macarena; Berjano, Enrique J

    2009-04-01

    The objectives of this study were to model the temperature progress of a pulsed radiofrequency (RF) power during RF heating of biological tissue, and to employ the hyperbolic heat transfer equation (HHTE), which takes the thermal wave behavior into account, and compare the results to those obtained using the heat transfer equation based on Fourier theory (FHTE). A theoretical model was built based on an active spherical electrode completely embedded in the biological tissue, after which HHTE and FHTE were analytically solved. We found three typical waveforms for the temperature progress depending on the relations between the dimensionless duration of the RF pulse delta(a) and the expression square root of lambda(rho-1), with lambda as the dimensionless thermal relaxation time of the tissue and rho as the dimensionless position. In the case of a unique RF pulse, the temperature at any location was the result of the overlapping of two different heat sources delayed for a duration delta(a) (each heat source being produced by a RF pulse of limitless duration). The most remarkable feature in the HHTE analytical solution was the presence of temperature peaks traveling through the medium at a finite speed. These peaks not only occurred during the RF power switch-on period but also during switch off. Finally, a physical explanation for these temperature peaks is proposed based on the interaction of forward and reverse thermal waves. All-purpose analytical solutions for FHTE and HHTE were obtained during pulsed RF heating of biological tissues, which could be used for any value of pulsing frequency and duty cycle.

  11. Swarm Intelligence for Urban Dynamics Modelling

    NASA Astrophysics Data System (ADS)

    Ghnemat, Rawan; Bertelle, Cyrille; Duchamp, Gérard H. E.

    2009-04-01

    In this paper, we propose swarm intelligence algorithms to deal with dynamical and spatial organization emergence. The goal is to model and simulate the developement of spatial centers using multi-criteria. We combine a decentralized approach based on emergent clustering mixed with spatial constraints or attractions. We propose an extension of the ant nest building algorithm with multi-center and adaptive process. Typically, this model is suitable to analyse and simulate urban dynamics like gentrification or the dynamics of the cultural equipment in urban area.

  12. Swarm Intelligence for Urban Dynamics Modelling

    SciTech Connect

    Ghnemat, Rawan; Bertelle, Cyrille; Duchamp, Gerard H. E.

    2009-04-16

    In this paper, we propose swarm intelligence algorithms to deal with dynamical and spatial organization emergence. The goal is to model and simulate the developement of spatial centers using multi-criteria. We combine a decentralized approach based on emergent clustering mixed with spatial constraints or attractions. We propose an extension of the ant nest building algorithm with multi-center and adaptive process. Typically, this model is suitable to analyse and simulate urban dynamics like gentrification or the dynamics of the cultural equipment in urban area.

  13. Dynamic process modeling with recurrent neural networks

    SciTech Connect

    You, Yong; Nikolaou, M. . Dept. of Chemical Engineering)

    1993-10-01

    Mathematical models play an important role in control system synthesis. However, due to the inherent nonlinearity, complexity and uncertainty of chemical processes, it is usually difficult to obtain an accurate model for a chemical engineering system. A method of nonlinear static and dynamic process modeling via recurrent neural networks (RNNs) is studied. An RNN model is a set of coupled nonlinear ordinary differential equations in continuous time domain with nonlinear dynamic node characteristics as well as both feed forward and feedback connections. For such networks, each physical input to a system corresponds to exactly one input to the network. The system's dynamics are captured by the internal structure of the network. The structure of RNN models may be more natural and attractive than that of feed forward neural network models, but computation time for training is longer. Simulation results show that RNNs can learn both steady-state relationships and process dynamics of continuous and batch, single-input/single-output and multi-input/multi-output systems in a simple and direct manner. Training of RNNs shows only small degradation in the presence of noise in the training data. Thus, RNNs constitute a feasible alternative to layered feed forward back propagation neural networks in steady-state and dynamic process modeling and model-based control.

  14. Battery electrochemical nonlinear/dynamic SPICE model

    SciTech Connect

    Glass, M.C.

    1996-12-31

    An Integrated Battery Model has been produced which accurately represents DC nonlinear battery behavior together with transient dynamics. The NiH{sub 2} battery model begins with a given continuous-function electrochemical math model. The math model for the battery consists of the sum of two electrochemical process DC currents, which are a function of the battery terminal voltage. This paper describes procedures for realizing a voltage-source SPICE model which implements the electrochemical equations using behavioral sources. The model merges the essentially DC non-linear behavior of the electrochemical model, together with the empirical AC dynamic terminal impedance from measured data. Thus the model integrates the short-term linear impedance behavior, with the long-term nonlinear DC resistance behavior. The long-duration non-Faradaic capacitive behavior of the battery is represented by a time constant. Outputs of the model include battery voltage/current, state-of-charge, and charge-current efficiency.

  15. Model systems for single molecule polymer dynamics

    PubMed Central

    Latinwo, Folarin

    2012-01-01

    Double stranded DNA (dsDNA) has long served as a model system for single molecule polymer dynamics. However, dsDNA is a semiflexible polymer, and the structural rigidity of the DNA double helix gives rise to local molecular properties and chain dynamics that differ from flexible chains, including synthetic organic polymers. Recently, we developed single stranded DNA (ssDNA) as a new model system for single molecule studies of flexible polymer chains. In this work, we discuss model polymer systems in the context of “ideal” and “real” chain behavior considering thermal blobs, tension blobs, hydrodynamic drag and force–extension relations. In addition, we present monomer aspect ratio as a key parameter describing chain conformation and dynamics, and we derive dynamical scaling relations in terms of this molecular-level parameter. We show that asymmetric Kuhn segments can suppress monomer–monomer interactions, thereby altering global chain dynamics. Finally, we discuss ssDNA in the context of a new model system for single molecule polymer dynamics. Overall, we anticipate that future single polymer studies of flexible chains will reveal new insight into the dynamic behavior of “real” polymers, which will highlight the importance of molecular individualism and the prevalence of non-linear phenomena. PMID:22956980

  16. Integration of Dynamic Models in Range Operations

    NASA Technical Reports Server (NTRS)

    Bardina, Jorge; Thirumalainambi, Rajkumar

    2004-01-01

    This work addresses the various model interactions in real-time to make an efficient internet based decision making tool for Shuttle launch. The decision making tool depends on the launch commit criteria coupled with physical models. Dynamic interaction between a wide variety of simulation applications and techniques, embedded algorithms, and data visualizations are needed to exploit the full potential of modeling and simulation. This paper also discusses in depth details of web based 3-D graphics and applications to range safety. The advantages of this dynamic model integration are secure accessibility and distribution of real time information to other NASA centers.

  17. A stochastic model of human gait dynamics

    NASA Astrophysics Data System (ADS)

    Ashkenazy, Yosef; M. Hausdorff, Jeffrey; Ch. Ivanov, Plamen; Eugene Stanley, H.

    2002-12-01

    We present a stochastic model of gait rhythm dynamics, based on transitions between different “neural centers”, that reproduces distinctive statistical properties of normal human walking. By tuning one model parameter, the transition (hopping) range, the model can describe alterations in gait dynamics from childhood to adulthood-including a decrease in the correlation and volatility exponents with maturation. The model also generates time series with multifractal spectra whose broadness depends only on this parameter. Moreover, we find that the volatility exponent increases monotonically as a function of the width of the multifractal spectrum, suggesting the possibility of a change in multifractality with maturation.

  18. The future dynamic world model

    NASA Astrophysics Data System (ADS)

    Karr, Thomas J.

    2014-10-01

    Defense and security forces exploit sensor data by means of a model of the world. They use a world model to geolocate sensor data, fuse it with other data, navigate platforms, recognize features and feature changes, etc. However, their need for situational awareness today exceeds the capabilities of their current world model for defense operations, despite the great advances of sensing technology in recent decades. I review emerging technologies that may enable a great improvement in the spatial and spectral coverage, the timeliness, and the functional insight of their world model.

  19. Multi-scale modelling and dynamics

    NASA Astrophysics Data System (ADS)

    Müller-Plathe, Florian

    Moving from a fine-grained particle model to one of lower resolution leads, with few exceptions, to an acceleration of molecular mobility, higher diffusion coefficient, lower viscosities and more. On top of that, the level of acceleration is often different for different dynamical processes as well as for different state points. While the reasons are often understood, the fact that coarse-graining almost necessarily introduces unpredictable acceleration of the molecular dynamics severely limits its usefulness as a predictive tool. There are several attempts under way to remedy these shortcoming of coarse-grained models. On the one hand, we follow bottom-up approaches. They attempt already when the coarse-graining scheme is conceived to estimate their impact on the dynamics. This is done by excess-entropy scaling. On the other hand, we also pursue a top-down development. Here we start with a very coarse-grained model (dissipative particle dynamics) which in its native form produces qualitatively wrong polymer dynamics, as its molecules cannot entangle. This model is modified by additional temporary bonds, so-called slip springs, to repair this defect. As a result, polymer melts and solutions described by the slip-spring DPD model show correct dynamical behaviour. Read more: ``Excess entropy scaling for the segmental and global dynamics of polyethylene melts'', E. Voyiatzis, F. Müller-Plathe, and M.C. Böhm, Phys. Chem. Chem. Phys. 16, 24301-24311 (2014). [DOI: 10.1039/C4CP03559C] ``Recovering the Reptation Dynamics of Polymer Melts in Dissipative Particle Dynamics Simulations via Slip-Springs'', M. Langeloth, Y. Masubuchi, M. C. Böhm, and F. Müller-Plathe, J. Chem. Phys. 138, 104907 (2013). [DOI: 10.1063/1.4794156].

  20. Stirling Engine Dynamic System Modeling

    NASA Technical Reports Server (NTRS)

    Nakis, Christopher G.

    2004-01-01

    The Thermo-Mechanical systems branch at the Glenn Research Center focuses a large amount time on Stirling engines. These engines will be used on missions where solar power is inefficient, especially in deep space. I work with Tim Regan and Ed Lewandowski who are currently developing and validating a mathematical model for the Stirling engines. This model incorporates all aspects of the system including, mechanical, electrical and thermodynamic components. Modeling is done through Simplorer, a program capable of running simulations of the model. Once created and then proven to be accurate, a model is used for developing new ideas for engine design. My largest specific project involves varying key parameters in the model and quantifying the results. This can all be done relatively trouble-free with the help of Simplorer. Once the model is complete, Simplorer will do all the necessary calculations. The more complicated part of this project is determining which parameters to vary. Finding key parameters depends on the potential for a value to be independently altered in the design. For example, a change in one dimension may lead to a proportional change to the rest of the model, and no real progress is made. Also, the ability for a changed value to have a substantial impact on the outputs of the system is important. Results will be condensed into graphs and tables with the purpose of better communication and understanding of the data. With the changing of these parameters, a more optimal design can be created without having to purchase or build any models. Also, hours and hours of results can be simulated in minutes. In the long run, using mathematical models can save time and money. Along with this project, I have many other smaller assignments throughout the summer. My main goal is to assist in the processes of model development, validation and testing.

  1. Uncertainty and Sensitivity in Surface Dynamics Modeling

    NASA Astrophysics Data System (ADS)

    Kettner, Albert J.; Syvitski, James P. M.

    2016-05-01

    Papers for this special issue on 'Uncertainty and Sensitivity in Surface Dynamics Modeling' heralds from papers submitted after the 2014 annual meeting of the Community Surface Dynamics Modeling System or CSDMS. CSDMS facilitates a diverse community of experts (now in 68 countries) that collectively investigate the Earth's surface-the dynamic interface between lithosphere, hydrosphere, cryosphere, and atmosphere, by promoting, developing, supporting and disseminating integrated open source software modules. By organizing more than 1500 researchers, CSDMS has the privilege of identifying community strengths and weaknesses in the practice of software development. We recognize, for example, that progress has been slow on identifying and quantifying uncertainty and sensitivity in numerical modeling of earth's surface dynamics. This special issue is meant to raise awareness for these important subjects and highlight state-of-the-art progress.

  2. Energy Balance Models and Planetary Dynamics

    NASA Technical Reports Server (NTRS)

    Domagal-Goldman, Shawn

    2012-01-01

    We know that planetary dynamics can have a significant affect on the climate of planets. Planetary dynamics dominate the glacial-interglacial periods on Earth, leaving a significant imprint on the geological record. They have also been demonstrated to have a driving influence on the climates of other planets in our solar system. We should therefore expect th.ere to be similar relationships on extrasolar planets. Here we describe a simple energy balance model that can predict the growth and thickness of glaciers, and their feedbacks on climate. We will also describe model changes that we have made to include planetary dynamics effects. This is the model we will use at the start of our collaboration to handle the influence of dynamics on climate.

  3. Modeling cell shape and dynamics on micropatterns

    PubMed Central

    Albert, Philipp J.; Schwarz, Ulrich S.

    2016-01-01

    ABSTRACT Adhesive micropatterns have become a standard tool to study cells under defined conditions. Applications range from controlling the differentiation and fate of single cells to guiding the collective migration of cell sheets. In long-term experiments, single cell normalization is challenged by cell division. For all of these setups, mathematical models predicting cell shape and dynamics can guide pattern design. Here we review recent advances in predicting and explaining cell shape, traction forces and dynamics on micropatterns. Starting with contour models as the simplest approach to explain concave cell shapes, we move on to network and continuum descriptions as examples for static models. To describe dynamic processes, cellular Potts, vertex and phase field models can be used. Different types of model are appropriate to address different biological questions and together, they provide a versatile tool box to predict cell behavior on micropatterns. PMID:26838278

  4. Haptics-based dynamic implicit solid modeling.

    PubMed

    Hua, Jing; Qin, Hong

    2004-01-01

    This paper systematically presents a novel, interactive solid modeling framework, Haptics-based Dynamic Implicit Solid Modeling, which is founded upon volumetric implicit functions and powerful physics-based modeling. In particular, we augment our modeling framework with a haptic mechanism in order to take advantage of additional realism associated with a 3D haptic interface. Our dynamic implicit solids are semi-algebraic sets of volumetric implicit functions and are governed by the principles of dynamics, hence responding to sculpting forces in a natural and predictable manner. In order to directly manipulate existing volumetric data sets as well as point clouds, we develop a hierarchical fitting algorithm to reconstruct and represent discrete data sets using our continuous implicit functions, which permit users to further design and edit those existing 3D models in real-time using a large variety of haptic and geometric toolkits, and visualize their interactive deformation at arbitrary resolution. The additional geometric and physical constraints afford more sophisticated control of the dynamic implicit solids. The versatility of our dynamic implicit modeling enables the user to easily modify both the geometry and the topology of modeled objects, while the inherent physical properties can offer an intuitive haptic interface for direct manipulation with force feedback.

  5. Synaptic dynamics: linear model and adaptation algorithm.

    PubMed

    Yousefi, Ali; Dibazar, Alireza A; Berger, Theodore W

    2014-08-01

    In this research, temporal processing in brain neural circuitries is addressed by a dynamic model of synaptic connections in which the synapse model accounts for both pre- and post-synaptic processes determining its temporal dynamics and strength. Neurons, which are excited by the post-synaptic potentials of hundred of the synapses, build the computational engine capable of processing dynamic neural stimuli. Temporal dynamics in neural models with dynamic synapses will be analyzed, and learning algorithms for synaptic adaptation of neural networks with hundreds of synaptic connections are proposed. The paper starts by introducing a linear approximate model for the temporal dynamics of synaptic transmission. The proposed linear model substantially simplifies the analysis and training of spiking neural networks. Furthermore, it is capable of replicating the synaptic response of the non-linear facilitation-depression model with an accuracy better than 92.5%. In the second part of the paper, a supervised spike-in-spike-out learning rule for synaptic adaptation in dynamic synapse neural networks (DSNN) is proposed. The proposed learning rule is a biologically plausible process, and it is capable of simultaneously adjusting both pre- and post-synaptic components of individual synapses. The last section of the paper starts with presenting the rigorous analysis of the learning algorithm in a system identification task with hundreds of synaptic connections which confirms the learning algorithm's accuracy, repeatability and scalability. The DSNN is utilized to predict the spiking activity of cortical neurons and pattern recognition tasks. The DSNN model is demonstrated to be a generative model capable of producing different cortical neuron spiking patterns and CA1 Pyramidal neurons recordings. A single-layer DSNN classifier on a benchmark pattern recognition task outperforms a 2-Layer Neural Network and GMM classifiers while having fewer numbers of free parameters and

  6. Theoretical modeling of RF ablation with internally cooled electrodes: comparative study of different thermal boundary conditions at the electrode-tissue interface.

    PubMed

    Rivera, María J; Molina, Juan A López; Trujillo, Macarena; Berjano, Enrique J

    2009-07-01

    Previous studies on computer modeling of RF ablation with cooled electrodes modeled the internal cooling circuit by setting surface temperature at the coolant temperature (i.e., Dirichlet condition, DC). Our objective was to compare the temperature profiles computed from different thermal boundary conditions at the electrode-tissue interface. We built an analytical one-dimensional model based on a spherical electrode. Four cases were considered: A) DC with uniform initial condition, B) DC with pre-cooling period, C) Boundary condition based on Newton's cooling law (NC) with uniform initial condition, and D) NC with a pre-cooling period. The results showed that for a long time (120 s), the profiles obtained with (Cases B and D) and without (Cases A and C) considering pre-cooling are very similar. However, for shorter times ( 30 s), Cases A and C overestimated the temperature at points away from the electrode-tissue interface. In the NC cases, this overestimation was more evident for higher values of the convective heat transfer coefficient (h). Finally, with NC, when h was increased the temperature profiles became more similar to those with DC. The results suggest that theoretical modeling of RF ablation with cooled electrodes should consider: 1) the modeling of a pre-cooling period, especially if one is interested in the thermal profiles registered at the beginning of RF application; and 2) NC rather than DC, especially for low flow in the internal circuit.

  7. Photodynamic therapy toward selective endometrial ablation

    NASA Astrophysics Data System (ADS)

    Tadir, Yona; Tromberg, Bruce J.; Krasieva, Tatiana B.; Berns, Michael W.

    1993-05-01

    Potential applications of photodynamic therapy for endometrial disease are discussed. Experimental models that may lead to diagnosis and treatment of endometriosis as well as selective endometrial ablation are summarized.

  8. Dynamic causal modeling with genetic algorithms.

    PubMed

    Pyka, M; Heider, D; Hauke, S; Kircher, T; Jansen, A

    2011-01-15

    In the last years, dynamic causal modeling has gained increased popularity in the neuroimaging community as an approach for the estimation of effective connectivity from functional magnetic resonance imaging (fMRI) data. The algorithm calls for an a priori defined model, whose parameter estimates are subsequently computed upon the given data. As the number of possible models increases exponentially with additional areas, it rapidly becomes inefficient to compute parameter estimates for all models in order to reveal the family of models with the highest posterior probability. In the present study, we developed a genetic algorithm for dynamic causal models and investigated whether this evolutionary approach can accelerate the model search. In this context, the configuration of the intrinsic, extrinsic and bilinear connection matrices represents the genetic code and Bayesian model selection serves as a fitness function. Using crossover and mutation, populations of models are created and compared with each other. The most probable ones survive the current generation and serve as a source for the next generation of models. Tests with artificially created data sets show that the genetic algorithm approximates the most plausible models faster than a random-driven brute-force search. The fitness landscape revealed by the genetic algorithm indicates that dynamic causal modeling has excellent properties for evolution-driven optimization techniques.

  9. Modeling Dynamic Regulatory Processes in Stroke.

    SciTech Connect

    McDermott, Jason E.; Jarman, Kenneth D.; Taylor, Ronald C.; Lancaster, Mary J.; Shankaran, Harish; Vartanian, Keri B.; Stevens, S.L.; Stenzel-Poore, Mary; Sanfilippo, Antonio P.

    2012-10-11

    The ability to examine in silico the behavior of biological systems can greatly accelerate the pace of discovery in disease pathologies, such as stroke, where in vivo experimentation is lengthy and costly. In this paper we describe an approach to in silico examination of blood genomic responses to neuroprotective agents and subsequent stroke through the development of dynamic models of the regulatory processes observed in the experimental gene expression data. First, we identified functional gene clusters from these data. Next, we derived ordinary differential equations (ODEs) relating regulators and functional clusters from the data. These ODEs were used to develop dynamic models that simulate the expression of regulated functional clusters using system dynamics as the modeling paradigm. The dynamic model has the considerable advantage of only requiring an initial starting state, and does not require measurement of regulatory influences at each time point in order to make accurate predictions. The manipulation of input model parameters, such as changing the magnitude of gene expression, made it possible to assess the behavior of the networks through time under varying conditions. We report that an optimized dynamic model can provide accurate predictions of overall system behavior under several different preconditioning paradigms.

  10. Cellular automata modeling of pedestrian's crossing dynamics.

    PubMed

    Zhang, Jin; Wang, Hui; Li, Ping

    2004-07-01

    Cellular automata modeling techniques and the characteristics of mixed traffic flow were used to derive the 2-dimensional model presented here for simulation of pedestrian's crossing dynamics. A conception of "stop point" is introduced to deal with traffic obstacles and resolve conflicts among pedestrians or between pedestrians and the other vehicles on the crosswalk. The model can be easily extended, is very efficient for simulation of pedestrian's crossing dynamics, can be integrated into traffic simulation software, and has been proved feasible by simulation experiments.

  11. Renal Ablation Update

    PubMed Central

    Khiatani, Vishal; Dixon, Robert G.

    2014-01-01

    Thermal ablative technologies have evolved considerably in the recent past and are now an important component of current clinical guidelines for the treatment of small renal masses. Both radiofrequency ablation and cryoablation have intermediate-term oncologic control that rivals surgical options, with favorable complication profiles. Studies comparing cryoablation and radiofrequency ablation show no significant difference in oncologic control or complication profile between the two modalities. Early data from small series with microwave ablation have shown similar promising results. Newer technologies including irreversible electroporation and high-intensity–focused ultrasound have theoretical advantages, but will require further research before becoming a routine part of the ablation armamentarium. The purpose of this review article is to discuss the current ablative technologies available, briefly review their mechanisms of action, discuss technical aspects of each, and provide current data supporting their use. PMID:25049445

  12. Length-dependent changes in contractile dynamics are blunted due to cardiac myosin binding protein-C ablation

    PubMed Central

    Mamidi, Ranganath; Gresham, Kenneth S.; Stelzer, Julian E.

    2014-01-01

    dynamic XB behavior due to changes in SL. PMID:25520665

  13. A dynamical model for the Utricularia trap.

    PubMed

    Llorens, Coraline; Argentina, Médéric; Bouret, Yann; Marmottant, Philippe; Vincent, Olivier

    2012-11-01

    We propose a model that captures the dynamics of a carnivorous plant, Utricularia inflata. This plant possesses tiny traps for capturing small aquatic animals. Glands pump water out of the trap, yielding a negative pressure difference between the plant and its surroundings. The trap door is set into a meta-stable state and opens quickly as an extra pressure is generated by the displacement of a potential prey. As the door opens, the pressure difference sucks the animal into the trap. We write an ODE model that captures all the physics at play. We show that the dynamics of the plant is quite similar to neuronal dynamics and we analyse the effect of a white noise on the dynamics of the trap. PMID:22859569

  14. Producing Uniform Lesion Pattern in HIFU Ablation

    NASA Astrophysics Data System (ADS)

    Zhou, Yufeng; Kargl, Steven G.; Hwang, Joo Ha

    2009-04-01

    High intensity focused ultrasound (HIFU) is emerging as a modality for treatment of solid tumors. The temperature at the focus can reach over 65° C denaturing cellular proteins resulting in coagulative necrosis. Typically, HIFU parameters are the same for each treated spot in most HIFU control systems. Because of thermal diffusion from nearby spots, the size of lesions will gradually become larger as the HIFU therapy progresses, which may cause insufficient treatment of initial spots, and over-treatment of later ones. It is found that the produced lesion pattern also depends on the scanning pathway. From the viewpoint of the physician creating uniform lesions and minimizing energy exposure are preferred in tumor ablation. An algorithm has been developed to adaptively determine the treatment parameters for every spot in a theoretical model in order to maintain similar lesion size throughout the HIFU therapy. In addition, the exposure energy needed using the traditional raster scanning is compared with those of two other scanning pathways, spiral scanning from the center to the outside and from the outside to the center. The theoretical prediction and proposed algorithm were further evaluated using transparent gel phantoms as a target. Digital images of the lesions were obtained, quantified, and then compared with each other. Altogether, dynamically changing treatment parameters can improve the efficacy and safety of HIFU ablation.

  15. Radiofrequency Ablation of Cancer

    SciTech Connect

    Friedman, Marc; Mikityansky, Igor; Kam, Anthony; Libutti, Steven K.; Walther, McClellan M.; Neeman, Ziv; Locklin, Julia K.; Wood, Bradford J.

    2004-09-15

    Radiofrequency ablation (RFA) has been used for over 18 years for treatment of nerve-related chronic pain and cardiac arrhythmias. In the last 10 years, technical developments have increased ablation volumes in a controllable, versatile, and relatively inexpensive manner. The host of clinical applications for RFA have similarly expanded. Current RFA equipment, techniques, applications, results, complications, and research avenues for local tumor ablation are summarized.

  16. Modeling of Dynamic FRC Formation

    NASA Astrophysics Data System (ADS)

    Mok, Yung; Barnes, Dan; Dettrick, Sean

    2010-11-01

    We have developed a 2-D resistive MHD code, Lamy Ridge, to simulate the entire FRC formation process in Tri Alpha's C2 device, including initial formation, translation, merging and settling into equilibrium. Two FRC's can be created simultaneously, and then translated toward each other so that they merge into a single FRC. The code couples the external circuits around the formation tubes to the partially ionized plasma inside. Plasma and neutral gas are treated as two fluids. Dynamic and energetic equations, which take into account ionization and charge exchange, are solved in a time advance manner. The geometric shape of the vessel is specified by a set of inputs that defines the boundaries, which are handled by a cut-cell algorithm in the code. Multiple external circuits and field coils can be easily added, removed or relocated through individual inputs. The design of the code is modular and flexible so that it can be applied to future devices. The results of the code are in reasonable agreement with experimental measurements on the C2 device.

  17. Dynamical Modeling of Surface Tension

    NASA Technical Reports Server (NTRS)

    Brackbill, Jeremiah U.; Kothe, Douglas B.

    1996-01-01

    In a recent review it is said that free-surface flows 'represent some of the difficult remaining challenges in computational fluid dynamics'. There has been progress with the development of new approaches to treating interfaces, such as the level-set method and the improvement of older methods such as the VOF method. A common theme of many of the new developments has been the regularization of discontinuities at the interface. One example of this approach is the continuum surface force (CSF) formulation for surface tension, which replaces the surface stress given by Laplace's equation by an equivalent volume force. Here, we describe how CSF formulation might be made more useful. Specifically, we consider a derivation of the CSF equations from a minimization of surface energy as outlined by Jacqmin (1996). This reformulation suggests that if one eliminates the computation of curvature in terms of a unit normal vector, parasitic currents may be eliminated. For this reformulation to work, it is necessary that transition region thickness be controlled. Various means for this, in addition to the one discussed by Jacqmin (1996), are discussed.

  18. Session 6: Dynamic Modeling and Systems Analysis

    NASA Technical Reports Server (NTRS)

    Csank, Jeffrey; Chapman, Jeffryes; May, Ryan

    2013-01-01

    These presentations cover some of the ongoing work in dynamic modeling and dynamic systems analysis. The first presentation discusses dynamic systems analysis and how to integrate dynamic performance information into the systems analysis. The ability to evaluate the dynamic performance of an engine design may allow tradeoffs between the dynamic performance and operability of a design resulting in a more efficient engine design. The second presentation discusses the Toolbox for Modeling and Analysis of Thermodynamic Systems (T-MATS). T-MATS is a Simulation system with a library containing the basic building blocks that can be used to create dynamic Thermodynamic Systems. Some of the key features include Turbo machinery components, such as turbines, compressors, etc., and basic control system blocks. T-MAT is written in the Matlab-Simulink environment and is open source software. The third presentation focuses on getting additional performance from the engine by allowing the limit regulators only to be active when a limit is danger of being violated. Typical aircraft engine control architecture is based on MINMAX scheme, which is designed to keep engine operating within prescribed mechanical/operational safety limits. Using a conditionally active min-max limit regulator scheme, additional performance can be gained by disabling non-relevant limit regulators

  19. Dispersive models describing mosquitoes’ population dynamics

    NASA Astrophysics Data System (ADS)

    Yamashita, W. M. S.; Takahashi, L. T.; Chapiro, G.

    2016-08-01

    The global incidences of dengue and, more recently, zica virus have increased the interest in studying and understanding the mosquito population dynamics. Understanding this dynamics is important for public health in countries where climatic and environmental conditions are favorable for the propagation of these diseases. This work is based on the study of nonlinear mathematical models dealing with the life cycle of the dengue mosquito using partial differential equations. We investigate the existence of traveling wave solutions using semi-analytical method combining dynamical systems techniques and numerical integration. Obtained solutions are validated through numerical simulations using finite difference schemes.

  20. Modeling the Dynamics of Compromised Networks

    SciTech Connect

    Soper, B; Merl, D M

    2011-09-12

    Accurate predictive models of compromised networks would contribute greatly to improving the effectiveness and efficiency of the detection and control of network attacks. Compartmental epidemiological models have been applied to modeling attack vectors such as viruses and worms. We extend the application of these models to capture a wider class of dynamics applicable to cyber security. By making basic assumptions regarding network topology we use multi-group epidemiological models and reaction rate kinetics to model the stochastic evolution of a compromised network. The Gillespie Algorithm is used to run simulations under a worst case scenario in which the intruder follows the basic connection rates of network traffic as a method of obfuscation.

  1. Local Electrical Dyssynchrony during Atrial Fibrillation: Theoretical Considerations and Initial Catheter Ablation Results

    PubMed Central

    Schäffer, Benjamin; Hoffmann, Boris A.; Ganesan, Anand N.; Schreiber, Doreen; Moser, Julia M.; Akbulak, Ruken Ö.; Sultan, Arian; Steven, Daniel; Maesen, Bart; Schotten, Ulrich; Meyer, Christian; Willems, Stephan

    2016-01-01

    Background Electrogram-based identification of the regions maintaining persistent Atrial Fibrillation (AF) is a subject of ongoing debate. Here, we explore the concept of local electrical dyssynchrony to identify AF drivers. Methods and Results Local electrical dyssynchrony was calculated using mean phase coherence. High-density epicardial mapping along with mathematical model were used to explore the link between local dyssynchrony and properties of wave conduction. High-density mapping showed a positive correlation between the dyssynchrony and number of fibrillatory waves (R2 = 0.68, p<0.001). In the mathematical model, virtual ablation at high dyssynchrony regions resulted in conduction regularization. The clinical study consisted of eighteen patients undergoing catheter ablation of persistent AF. High-density maps of left atrial (LA) were constructed using a circular mapping catheter. After pulmonary vein isolation, regions with the top 10% of the highest dyssynchrony in LA were targeted during ablation and followed with ablation of complex atrial electrograms. Catheter ablation resulted in termination during ablation at high dyssynchrony regions in 7 (41%) patients. In another 4 (24%) patients, transient organization was observed. In 6 (35%) there was no clear effect. Long-term follow-up showed 65% AF freedom at 1 year and 22% at 2 years. Conclusions Local electrical dyssynchrony provides a reasonable estimator of regional AF complexity defined as the number of fibrillatory waves. Additionally, it points to regions of dynamical instability related with action potential alternans. However, despite those characteristics, its utility in guiding catheter ablation of AF is limited suggesting other factors are responsible for AF persistence. PMID:27780243

  2. Alternative models for cyclic lemming dynamics.

    PubMed

    Wang, Hao; Kuang, Yang

    2007-01-01

    Many natural population growths and interactions are affected by seasonal changes, suggesting that these natural population dynamics should be modeled by nonautonomous differential equations instead of autonomous differential equations. Through a series of carefully derived models of the well documented high-amplitude, large-period fluctuations of lemming populations, we argue that when appropriately formulated, autonomous differential equations may capture much of the desirable rich dynamics, such as the existence of a periodic solution with period and amplitude close to that of approximately periodic solutions produced by the more natural but mathematically daunt ing nonautonomous models. We start this series of models from the Barrow model, a well formulated model for the dynamics of food-lemming interaction at Point Barrow (Alaska, USA) with sufficient experimental data. Our work suggests that an autonomous system can indeed be a good approximation to the moss-lemming dynamics at Point Barrow. This, together with our bifurcation analysis, indicates that neither seasonal factors (expressed by time dependent moss growth rate and lemming death rate in the Barrow model) nor the moss growth rate and lemming death rate are the main culprits of the observed multi-year lemming cycles. We suspect that the main culprits may include high lemming predation rate, high lemming birth rate, and low lemming self-limitation rate.

  3. Instabilities of ablation fronts in inertial confinement fusion: A comparison with flames

    NASA Astrophysics Data System (ADS)

    Clavin, P.; Masse, L.

    2004-02-01

    A comparison with flames sheds new light on the dynamics of ablation fronts in inertial confinement fusion (ICF). The mathematical formulation of the problem in ICF is the same as for flames propagating upwards. The difference concerns the Froude number Fr, yielding a different order of magnitude for the nondimensional wave number of the marginally stable disturbances. When the thermal conductivity varies strongly, as is the case in ICF, a wide range of characteristic (diffusive) lengths is involved across the wave structure. For disturbances with intermediate wavelengths, a "universal" diffusive relaxation rate of thermal waves is exhibited with no dependence on the heat conductivity. This is a key point for describing the dynamics of strongly accelerated ablation fronts whose marginally stable wavelength is much shorter than the total wave thickness. The coupling of hydrodynamics and heat conduction is analyzed in a way similar to flame theory, through the derivation of a kinematic relation for the ablation front including its thermal relaxation. A transition between the regimes of flames and ablation fronts in ICF is exhibited with decreasing Fr. For a moderate acceleration, Fr≫1, the result for flames is recovered. For a large acceleration, Fr of order unity, the thermal relaxation, when coupled with hydrodynamics, is shown to damp out the Darrieus-Landau instability, yielding the known result in ICF for strongly accelerated ablation fronts. For a wide class of models, including the simple two-length-scale model, the description is shown to be independent of the model. A weakly nonlinear analysis, valid irrespective of the number of unstable modes, is carried out for describing the early development of nonlinear structures of the ablation front in ICF. The role of the Darrieus-Landau instability at the early stage of irradiation is pointed out.

  4. Error dynamics in shell models for turbulence

    NASA Astrophysics Data System (ADS)

    De Cruz, Lesley; Vannitsem, Stéphane

    2013-04-01

    A deep understanding of the error dynamics in turbulent systems is crucial to estimate the horizon of predictability, and to quantify the impact of initial-condition (IC) and model errors on the statistical characteristics of ensemble prediction systems. We present a study of the dynamics of combined IC and model errors in a turbulent system. We use the Sabra shell model [1], a spectral model which captures the characteristic properties of a turbulent system using a low number of variables (of the order of 50). The analytical properties of the short-term error dynamics in the Sabra shell model are investigated using the methodology described in Ref. [2], and compared to numerical results. Of particular interest is the property of a dissipative system that the mean squared error (MSE) reaches a minimum shortly after the introduction of an IC error. The distribution of the minimum-error times is investigated, and the spatial-scale dependence of the error dynamics is discussed. At longer time scales, our simulations confirm the well-known fact that an arbitrarily small error in the initial conditions contaminates the integral scale in a time that is independent of the scale of the initial error. Finally, we report on the error dynamics in the presence of a crossover between 3D and 2D turbulence, known to characterise the atmosphere. References [1] V. S. L'vov, E. Podivilov, A. Pomyalov, I. Procaccia, and D. Vandembroucq. Improved shell model of turbulence. Physical Review E, 58:1811-1822, August 1998. [2] C. Nicolis, R. A. P. Perdigao, and S. Vannitsem. Dynamics of Prediction Errors under the Combined Effect of Initial Condition and Model Errors. Journal of Atmospheric Sciences, 66:766, 2009.

  5. Nonlinear Dynamic Models in Advanced Life Support

    NASA Technical Reports Server (NTRS)

    Jones, Harry

    2002-01-01

    To facilitate analysis, ALS systems are often assumed to be linear and time invariant, but they usually have important nonlinear and dynamic aspects. Nonlinear dynamic behavior can be caused by time varying inputs, changes in system parameters, nonlinear system functions, closed loop feedback delays, and limits on buffer storage or processing rates. Dynamic models are usually cataloged according to the number of state variables. The simplest dynamic models are linear, using only integration, multiplication, addition, and subtraction of the state variables. A general linear model with only two state variables can produce all the possible dynamic behavior of linear systems with many state variables, including stability, oscillation, or exponential growth and decay. Linear systems can be described using mathematical analysis. Nonlinear dynamics can be fully explored only by computer simulations of models. Unexpected behavior is produced by simple models having only two or three state variables with simple mathematical relations between them. Closed loop feedback delays are a major source of system instability. Exceeding limits on buffer storage or processing rates forces systems to change operating mode. Different equilibrium points may be reached from different initial conditions. Instead of one stable equilibrium point, the system may have several equilibrium points, oscillate at different frequencies, or even behave chaotically, depending on the system inputs and initial conditions. The frequency spectrum of an output oscillation may contain harmonics and the sums and differences of input frequencies, but it may also contain a stable limit cycle oscillation not related to input frequencies. We must investigate the nonlinear dynamic aspects of advanced life support systems to understand and counter undesirable behavior.

  6. Dynamic Model for Life History of Scyphozoa

    PubMed Central

    Xie, Congbo; Fan, Meng; Wang, Xin; Chen, Ming

    2015-01-01

    A two-state life history model governed by ODEs is formulated to elucidate the population dynamics of jellyfish and to illuminate the triggering mechanism of its blooms. The polyp-medusa model admits trichotomous global dynamic scenarios: extinction, polyps survival only, and both survival. The population dynamics sensitively depend on several biotic and abiotic limiting factors such as substrate, temperature, and predation. The combination of temperature increase, substrate expansion, and predator diminishment acts synergistically to create a habitat that is more favorable for jellyfishes. Reducing artificial marine constructions, aiding predator populations, and directly controlling the jellyfish population would help to manage the jellyfish blooms. The theoretical analyses and numerical experiments yield several insights into the nature underlying the model and shed some new light on the general control strategy for jellyfish. PMID:26114642

  7. Dynamic Model for Life History of Scyphozoa.

    PubMed

    Xie, Congbo; Fan, Meng; Wang, Xin; Chen, Ming

    2015-01-01

    A two-state life history model governed by ODEs is formulated to elucidate the population dynamics of jellyfish and to illuminate the triggering mechanism of its blooms. The polyp-medusa model admits trichotomous global dynamic scenarios: extinction, polyps survival only, and both survival. The population dynamics sensitively depend on several biotic and abiotic limiting factors such as substrate, temperature, and predation. The combination of temperature increase, substrate expansion, and predator diminishment acts synergistically to create a habitat that is more favorable for jellyfishes. Reducing artificial marine constructions, aiding predator populations, and directly controlling the jellyfish population would help to manage the jellyfish blooms. The theoretical analyses and numerical experiments yield several insights into the nature underlying the model and shed some new light on the general control strategy for jellyfish.

  8. Dynamic Model for Life History of Scyphozoa.

    PubMed

    Xie, Congbo; Fan, Meng; Wang, Xin; Chen, Ming

    2015-01-01

    A two-state life history model governed by ODEs is formulated to elucidate the population dynamics of jellyfish and to illuminate the triggering mechanism of its blooms. The polyp-medusa model admits trichotomous global dynamic scenarios: extinction, polyps survival only, and both survival. The population dynamics sensitively depend on several biotic and abiotic limiting factors such as substrate, temperature, and predation. The combination of temperature increase, substrate expansion, and predator diminishment acts synergistically to create a habitat that is more favorable for jellyfishes. Reducing artificial marine constructions, aiding predator populations, and directly controlling the jellyfish population would help to manage the jellyfish blooms. The theoretical analyses and numerical experiments yield several insights into the nature underlying the model and shed some new light on the general control strategy for jellyfish. PMID:26114642

  9. Modeling the dynamics of ant colony optimization.

    PubMed

    Merkle, Daniel; Middendorf, Martin

    2002-01-01

    The dynamics of Ant Colony Optimization (ACO) algorithms is studied using a deterministic model that assumes an average expected behavior of the algorithms. The ACO optimization metaheuristic is an iterative approach, where in every iteration, artificial ants construct solutions randomly but guided by pheromone information stemming from former ants that found good solutions. The behavior of ACO algorithms and the ACO model are analyzed for certain types of permutation problems. It is shown analytically that the decisions of an ant are influenced in an intriguing way by the use of the pheromone information and the properties of the pheromone matrix. This explains why ACO algorithms can show a complex dynamic behavior even when there is only one ant per iteration and no competition occurs. The ACO model is used to describe the algorithm behavior as a combination of situations with different degrees of competition between the ants. This helps to better understand the dynamics of the algorithm when there are several ants per iteration as is always the case when using ACO algorithms for optimization. Simulations are done to compare the behavior of the ACO model with the ACO algorithm. Results show that the deterministic model describes essential features of the dynamics of ACO algorithms quite accurately, while other aspects of the algorithms behavior cannot be found in the model. PMID:12227995

  10. Dynamic modeling of solar dynamic components and systems

    NASA Astrophysics Data System (ADS)

    Hochstein, John I.; Korakianitis, T.

    1992-09-01

    The purpose of this grant was to support NASA in modeling efforts to predict the transient dynamic and thermodynamic response of the space station solar dynamic power generation system. In order to meet the initial schedule requirement of providing results in time to support installation of the system as part of the initial phase of space station, early efforts were executed with alacrity and often in parallel. Initially, methods to predict the transient response of a Rankine as well as a Brayton cycle were developed. Review of preliminary design concepts led NASA to select a regenerative gas-turbine cycle using a helium-xenon mixture as the working fluid and, from that point forward, the modeling effort focused exclusively on that system. Although initial project planning called for a three year period of performance, revised NASA schedules moved system installation to later and later phases of station deployment. Eventually, NASA selected to halt development of the solar dynamic power generation system for space station and to reduce support for this project to two-thirds of the original level.

  11. Dynamic Modeling of Solar Dynamic Components and Systems

    NASA Technical Reports Server (NTRS)

    Hochstein, John I.; Korakianitis, T.

    1992-01-01

    The purpose of this grant was to support NASA in modeling efforts to predict the transient dynamic and thermodynamic response of the space station solar dynamic power generation system. In order to meet the initial schedule requirement of providing results in time to support installation of the system as part of the initial phase of space station, early efforts were executed with alacrity and often in parallel. Initially, methods to predict the transient response of a Rankine as well as a Brayton cycle were developed. Review of preliminary design concepts led NASA to select a regenerative gas-turbine cycle using a helium-xenon mixture as the working fluid and, from that point forward, the modeling effort focused exclusively on that system. Although initial project planning called for a three year period of performance, revised NASA schedules moved system installation to later and later phases of station deployment. Eventually, NASA selected to halt development of the solar dynamic power generation system for space station and to reduce support for this project to two-thirds of the original level.

  12. Record Dynamics and the Parking Lot Model for granular dynamics

    NASA Astrophysics Data System (ADS)

    Sibani, Paolo; Boettcher, Stefan

    Also known for its application to granular compaction (E. Ben-Naim et al., Physica D, 1998), the Parking Lot Model (PLM) describes the random parking of identical cars in a strip with no marked bays. In the thermally activated version considered, cars can be removed at an energy cost and, in thermal equilibrium, their average density increases as temperature decreases. However, equilibration at high density becomes exceedingly slow and the system enters an aging regime induced by a kinematic constraint, the fact that parked cars may not overlap. As parking an extra car reduces the available free space,the next parking event is even harder to achieve. Records in the number of parked cars mark the salient features of the dynamics and are shown to be well described by the log-Poisson statistics known from other glassy systems with record dynamics. Clusters of cars whose positions must be rearranged to make the next insertion possible have a length scale which grows logarithmically with age, while their life-time grows exponentially with size. The implications for a recent cluster model of colloidal dynamics,(S. Boettcher and P. Sibani, J. Phys.: Cond. Matter, 2011 N. Becker et al., J. Phys.: Cond. Matter, 2014) are discussed. Support rom the Villum Foundation is gratefully acknowledged.

  13. Efficient dynamic models of tensegrity systems

    NASA Astrophysics Data System (ADS)

    Skelton, Robert

    2009-03-01

    The multi-body dynamics appear in a new form, as a matrix differential equation, rather than the traditional vector differential equation. The model has a constant mass matrix, and the equations are non-minimal. A specific focus of this paper is tensegrity systems. A tensegrity system requires prestress for stabilization of the configuration of rigid bodies and tensile members. This paper provides an efficient model for both static and dynamic behavior of such systems, specialized for the case when the rigid bodies are axi-symmetric rods.

  14. Modeling emotional dynamics : currency versus field.

    SciTech Connect

    Sallach, D .L.; Decision and Information Sciences; Univ. of Chicago

    2008-08-01

    Randall Collins has introduced a simplified model of emotional dynamics in which emotional energy, heightened and focused by interaction rituals, serves as a common denominator for social exchange: a generic form of currency, except that it is active in a far broader range of social transactions. While the scope of this theory is attractive, the specifics of the model remain unconvincing. After a critical assessment of the currency theory of emotion, a field model of emotion is introduced that adds expressiveness by locating emotional valence within its cognitive context, thereby creating an integrated orientation field. The result is a model which claims less in the way of motivational specificity, but is more satisfactory in modeling the dynamic interaction between cognitive and emotional orientations at both individual and social levels.

  15. Automated planning of ablation targets in atrial fibrillation treatment

    NASA Astrophysics Data System (ADS)

    Keustermans, Johannes; De Buck, Stijn; Heidbüchel, Hein; Suetens, Paul

    2011-03-01

    Catheter based radio-frequency ablation is used as an invasive treatment of atrial fibrillation. This procedure is often guided by the use of 3D anatomical models obtained from CT, MRI or rotational angiography. During the intervention the operator accurately guides the catheter to prespecified target ablation lines. The planning stage, however, can be time consuming and operator dependent which is suboptimal both from a cost and health perspective. Therefore, we present a novel statistical model-based algorithm for locating ablation targets from 3D rotational angiography images. Based on a training data set of 20 patients, consisting of 3D rotational angiography images with 30 manually indicated ablation points, a statistical local appearance and shape model is built. The local appearance model is based on local image descriptors to capture the intensity patterns around each ablation point. The local shape model is constructed by embedding the ablation points in an undirected graph and imposing that each ablation point only interacts with its neighbors. Identifying the ablation points on a new 3D rotational angiography image is performed by proposing a set of possible candidate locations for each ablation point, as such, converting the problem into a labeling problem. The algorithm is validated using a leave-one-out-approach on the training data set, by computing the distance between the ablation lines obtained by the algorithm and the manually identified ablation points. The distance error is equal to 3.8+/-2.9 mm. As ablation lesion size is around 5-7 mm, automated planning of ablation targets by the presented approach is sufficiently accurate.

  16. A Monodisperse Aerosol Dynamics Model Mono32

    NASA Astrophysics Data System (ADS)

    Pirjola, L.

    A recently developed aerosol dynamics model MONO32 (and MULTIMONO) (Pir- jola and Kulmala, 2000) is a Lagrangian type box model which uses mondisperse representation for particle size distribution. The model takes into account gas-phase chemistry and aerosol dynamics including emissions and dry deposition of gases and particles, chemical reactions in the gas phase, homogeneous binary H2SO4-H2O or ternary H2SO4-H2O-NH3 nucleation, multicomponent condensation of H2SO4, H2O, HNO3, NH3 and some organic vapour onto particles as well as inter- and in- tramode coagulation of particles. Particles can consist of soluble material such as sul- phate, nitrate, ammonium, sodium cloride, as well as insoluble material such as or- ganic carbon, elemental carbon and mineral dust. Hygroscopic properties and growth of particles were studied by the model. Simulations predicted that nucleation mode particles grew with a growth rate of 2.5-3 nm/h if the source rate of a condensable nonvolatile organic vapour exceeded 10^5 cm^-3 s^-1 and the condensation sink of the pre-existing particles was 0.9x10^-3 s^-1. These results are in good agreemnet with the measurements in Southern Finland. Further, these particles are able to grow to CCN sizes, thus affecting climate. The model was compared very well with the sectional model AEROFOR2 (Pirjola and Kulmala, 2001). It is physically sound and computa- tionally efficient model also for using as a module for regional transport models. Pirjola, L. and Kulmala, M. (2000) Aerosol dynamical model MULTIMONO, Boreal research 5, 361-372. Pirjola, L. and Kulmala, M. (2001) Development of particle size and composition distribution with aerosol dynamics model AEROFOR2. Tellus 53B, 491-509. Pirjola, L., Korhonen, H. and Kulmala, M. (2002) Condensation/ evaporation of insoluble organic vapour as functions of source rate and saturation vapour pressure. J. Geophys. Res. (in press).

  17. Potential enhancement of intravenous nano-hydroxyapatite in high-intensity focused ultrasound ablation for treating hepatocellular carcinoma in a rabbit model

    PubMed Central

    LIU, LIPING; XIAO, ZIWEN; XIAO, YANBING; WANG, ZHIBIAO; LI, FAQI; LI, MAOPING; PENG, XIAOQIONG

    2014-01-01

    The aim of the present study was to evaluate the safety and efficiency of an intravenously delivered nano-hydroxyapatite (Nano-HA) solution into a rabbit model (Oryctolagus cuniculus) to determine the potential enhancement of high-intensity focused ultrasound (HIFU) for the ablation of hepatocellular carcinoma (HCC) in liver tissue. The present study clearly indicated that the intravenous delivery of large quantities of Nano-HA into the body of the rabbit model over relatively short periods of time may be absorbed by the hepatic reticuloendothelial system. Subsequent HIFU treatment for HCC, as well as intravenous Nano-HA, produced a rapid increase in temperature and an enlargement of the coagulated necrotic area during ablation in the in vivo and ex vivo environments. In addition, it was found that the therapeutic doses of Nano-HA produced mild and transient abnormalities in the normal renal function and hepatic enzymes during the first 24 h following administration. The results of the current study indicated that the combination of Nano-HA and HIFU may provide a safe and effective alternative to conventional surgical procedures. PMID:24765161

  18. Femtosecond laser lithotripsy: feasibility and ablation mechanism

    NASA Astrophysics Data System (ADS)

    Qiu, Jinze; Teichman, Joel M. H.; Wang, Tianyi; Neev, Joseph; Glickman, Randolph D.; Chan, Kin Foong; Milner, Thomas E.

    2010-03-01

    Light emitted from a femtosecond laser is capable of plasma-induced ablation of various materials. We tested the feasibility of utilizing femtosecond-pulsed laser radiation (λ=800 nm, 140 fs, 0.9 mJ/pulse) for ablation of urinary calculi. Ablation craters were observed in human calculi of greater than 90% calcium oxalate monohydrate (COM), cystine (CYST), or magnesium ammonium phosphate hexahydrate (MAPH). Largest crater volumes were achieved on CYST stones, among the most difficult stones to fragment using Holmium:YAG (Ho:YAG) lithotripsy. Diameter of debris was characterized using optical microscopy and found to be less than 20 μm, substantially smaller than that produced by long-pulsed Ho:YAG ablation. Stone retropulsion, monitored by a high-speed camera system with a spatial resolution of 15 μm, was negligible for stones with mass as small as 0.06 g. Peak shock wave pressures were less than 2 bars, measured by a polyvinylidene fluoride (PVDF) needle hydrophone. Ablation dynamics were visualized and characterized with pump-probe imaging and fast flash photography and correlated to shock wave pressures. Because femtosecond-pulsed laser ablates urinary calculi of soft and hard compositions, with micron-sized debris, negligible stone retropulsion, and small shock wave pressures, we conclude that the approach is a promising candidate technique for lithotripsy.

  19. Sprayable lightweight ablative coating

    NASA Technical Reports Server (NTRS)

    Simpson, William G. (Inventor); Sharpe, Max H. (Inventor); Hill, William E. (Inventor)

    1991-01-01

    An improved lightweight, ablative coating is disclosed that may be spray applied and cured without the development of appreciable shrinkage cracks. The ablative mixture consists essentially of phenolic microballoons, hollow glass spheres, glass fibers, ground cork, a flexibilized resin binder, and an activated colloidal clay.

  20. Modeling biological pathway dynamics with timed automata.

    PubMed

    Schivo, Stefano; Scholma, Jetse; Wanders, Brend; Urquidi Camacho, Ricardo A; van der Vet, Paul E; Karperien, Marcel; Langerak, Rom; van de Pol, Jaco; Post, Janine N

    2014-05-01

    Living cells are constantly subjected to a plethora of environmental stimuli that require integration into an appropriate cellular response. This integration takes place through signal transduction events that form tightly interconnected networks. The understanding of these networks requires capturing their dynamics through computational support and models. ANIMO (analysis of Networks with Interactive Modeling) is a tool that enables the construction and exploration of executable models of biological networks, helping to derive hypotheses and to plan wet-lab experiments. The tool is based on the formalism of Timed Automata, which can be analyzed via the UPPAAL model checker. Thanks to Timed Automata, we can provide a formal semantics for the domain-specific language used to represent signaling networks. This enforces precision and uniformity in the definition of signaling pathways, contributing to the integration of isolated signaling events into complex network models. We propose an approach to discretization of reaction kinetics that allows us to efficiently use UPPAAL as the computational engine to explore the dynamic behavior of the network of interest. A user-friendly interface hides the use of Timed Automata from the user, while keeping the expressive power intact. Abstraction to single-parameter kinetics speeds up construction of models that remain faithful enough to provide meaningful insight. The resulting dynamic behavior of the network components is displayed graphically, allowing for an intuitive and interactive modeling experience. PMID:24808226

  1. A Novel Virus-Patch Dynamic Model

    PubMed Central

    Yang, Lu-Xing; Yang, Xiaofan

    2015-01-01

    The distributed patch dissemination strategies are a promising alternative to the conventional centralized patch dissemination strategies. This paper aims to establish a theoretical framework for evaluating the effectiveness of distributed patch dissemination mechanism. Assuming that the Internet offers P2P service for every pair of nodes on the network, a dynamic model capturing both the virus propagation mechanism and the distributed patch dissemination mechanism is proposed. This model takes into account the infected removable storage media and hence captures the interaction of patches with viruses better than the original SIPS model. Surprisingly, the proposed model exhibits much simpler dynamic properties than the original SIPS model. Specifically, our model admits only two potential (viral) equilibria and undergoes a fold bifurcation. The global stabilities of the two equilibria are determined. Consequently, the dynamical properties of the proposed model are fully understood. Furthermore, it is found that reducing the probability per unit time of disconnecting a node from the Internet benefits the containment of electronic viruses. PMID:26368556

  2. Modeling share dynamics by extracting competition structure

    NASA Astrophysics Data System (ADS)

    Kimura, Masahiro; Saito, Kazumi; Ueda, Naonori

    2004-11-01

    We propose a new method for analyzing multivariate time-series data governed by competitive dynamics such as fluctuations in the number of visitors to Web sites that form a market. To achieve this aim, we construct a probabilistic dynamical model using a replicator equation and derive its learning algorithm. This method is implemented for both categorizing the sites into groups of competitors and predicting the future shares of the sites based on the observed time-series data. We confirmed experimentally, using synthetic data, that the method successfully identifies the true model structure, and exhibits better prediction performance than conventional methods that leave competitive dynamics out of consideration. We also experimentally demonstrated, using real data of visitors to 20 Web sites offering streaming video contents, that the method suggested a reasonable competition structure that conventional methods failed to find and that it outperformed them in terms of predictive performance.

  3. Polarizable protein model for Dissipative Particle Dynamics

    NASA Astrophysics Data System (ADS)

    Peter, Emanuel; Lykov, Kirill; Pivkin, Igor

    2015-11-01

    In this talk, we present a novel polarizable protein model for the Dissipative Particle Dynamics (DPD) simulation technique, a coarse-grained particle-based method widely used in modeling of fluid systems at the mesoscale. We employ long-range electrostatics and Drude oscillators in combination with a newly developed polarizable water model. The protein in our model is resembled by a polarizable backbone and a simplified representation of the sidechains. We define the model parameters using the experimental structures of 2 proteins: TrpZip2 and TrpCage. We validate the model on folding of five other proteins and demonstrate that it successfully predicts folding of these proteins into their native conformations. As a perspective of this model, we will give a short outlook on simulations of protein aggregation in the bulk and near a model membrane, a relevant process in several Amyloid diseases, e.g. Alzheimer's and Diabetes II.

  4. Radiofrequency ablation of the basivertebral nerve as potential treatment of back pain: pathologic assessment in an ovine model (Invited Paper)

    NASA Astrophysics Data System (ADS)

    Hoopes, P. J.; Eskey, Cliff J.; Attawia, Mohammed; Patel, Samit J.; Ryan, T. P.; Pellegrino, Richard; Bergeron, Jeffrey A.

    2005-04-01

    Pathological involvement of the basivertebral nerve (BVN), an intraosseous vertebral nerve, may play a significant role in some forms of back pain. This study was designed to assess the feasibility and effects of thermal ablation of the lumbar basivertebral nerve in mature sheep. Sixteen adult female sheep weighing 65-80 kg were anesthetized and positioned for ventral recumbent surgery. Under fluoroscopic guidance, two bilarterally oposed 5mm active length rediofrequency (RF) electrodes (1.65mm diameter were perfutaneously placed in select lumbar vertebrae at a relative angle of 70 degrees with a 5 mm tip separation. The elctrodes were advanced to the region of the vertebral bodies which contained the BVN. A thermal dose of 95° C/720 seconds was administered. Animals were survived for 2, 14, 90, or 180 days post-treatment. Clinical, radiologic and pathologic investigations were performed to determine the effect of the heat on the BVN and associated tissues. Thermal damage to the basivertebral neurovascular bundle was characterized by early hemorrhage and necrosis, followed by inflammation and fibrosis. Although there wasa significant revascularization of the treated bone marow regions, there was no evidence of basivertebral nerve survival or regeneration regeneration. In addition to ablation of teh basivertebral nerovascular bundle, the areas receiving the greatest treatment demonstrated initial mild local osteolysis and demineralization of the vertebral body bone and regional depopulation of the vertebral bone marrow cellular elements. Significant bone remodeling in the affected areas had begun by 14 days post-treatment. Bone remodeling was characterized by conventional osteoblast proliferation, osteoid deposition, and mineralization. This study demonstrated the ability to accurately, reproducibly, and safely ablate the basivertebral nerve and neurovascular bundle in mature sheep using a fluoroscopically guided percutaneously delivered radiofrequency technique.

  5. System and mathematical modeling of quadrotor dynamics

    NASA Astrophysics Data System (ADS)

    Goodman, Jacob M.; Kim, Jinho; Gadsden, S. Andrew; Wilkerson, Stephen A.

    2015-05-01

    Unmanned aerial systems (UAS) are becoming increasingly visible in our daily lives; and range in operation from search and rescue, monitoring hazardous environments, and to the delivery of goods. One of the most popular UAS are based on a quad-rotor design. These are typically small devices that rely on four propellers for lift and movement. Quad-rotors are inherently unstable, and rely on advanced control methodologies to keep them operating safely and behaving in a predictable and desirable manner. The control of these devices can be enhanced and improved by making use of an accurate dynamic model. In this paper, we examine a simple quadrotor model, and note some of the additional dynamic considerations that were left out. We then compare simulation results of the simple model with that of another comprehensive model.

  6. Combination radiofrequency (RF) ablation and IV liposomal heat shock protein suppression: Reduced tumor growth and increased animal endpoint survival in a small animal tumor model

    PubMed Central

    Yang, Wei; Ahmed, Muneeb; Tasawwar, Beenish; Levchenko, Tatynana; Sawant, Rupa R.; Torchilin, Vladimir; Goldberg, S. Nahum

    2012-01-01

    Background To investigate the effect of IV liposomal quercetin (a known down-regulator of heat shock proteins) alone and with liposomal doxorubicin on tumor growth and end-point survival when combined with radiofrequency (RF) tumor ablation in a rat tumor model. Methods Solitary subcutaneous R3230 mammary adenocarcinoma tumors (1.3–1.5 cm) were implanted in 48 female Fischer rats. Initially, 32 tumors (n=8, each group) were randomized into four experimental groups: (a) conventional monopolar RF alone (70°C for 5 min), (b) IV liposomal quercetin alone (1 mg/kg), (c) IV liposomal quercetin followed 24hr later with RF, and (d) no treatment. Next, 16 additional tumors were randomized into two groups (n=8, each) that received a combined RF and liposomal doxorubicin (15 min post-RF, 8 mg/kg) either with or without liposomal quercetin. Kaplan-Meier survival analysis was performed using a tumor diameter of 3.0 cm as the defined survival endpoint. Results Differences in endpoint survival and tumor doubling time among the groups were highly significant (P<0.001). Endpoint survivals were 12.5±2.2 days for the control group, 16.6±2.9 days for tumors treated with RF alone, 15.5±2.1days for tumors treated with liposomal quercetin alone, and 22.0±3.9 days with combined RF and quercetin. Additionally, combination quercetin/RF/doxorubicin therapy resulted in the longest survival (48.3±20.4 days), followed by RF/doxorubicin (29.9±3.8 days). Conclusions IV liposomal quercetin in combination with RF ablation reduces tumor growth rates and improves animal endpoint survival. Further increases in endpoint survival can be seen by adding an additional anti-tumor adjuvant agent liposomal doxorubicin. This suggests that targeting several post-ablation processes with multi-drug nanotherapies can increase overall ablation efficacy. PMID:22230341

  7. Modeling of Reactor Kinetics and Dynamics

    SciTech Connect

    Matthew Johnson; Scott Lucas; Pavel Tsvetkov

    2010-09-01

    In order to model a full fuel cycle in a nuclear reactor, it is necessary to simulate the short time-scale kinetic behavior of the reactor as well as the long time-scale dynamics that occur with fuel burnup. The former is modeled using the point kinetics equations, while the latter is modeled by coupling fuel burnup equations with the kinetics equations. When the equations are solved simultaneously with a nonlinear equation solver, the end result is a code with the unique capability of modeling transients at any time during a fuel cycle.

  8. Developmental Stages in Dynamic Plant Growth Models

    NASA Astrophysics Data System (ADS)

    Maclean, Heather; Dochain, Denis; Waters, Geoff; Stasiak, Michael; Dixon, Mike; Van Der Straeten, Dominique

    2011-09-01

    During the growth of red beet plants in a closed environment plant growth chamber, a change in metabolism was observed (decreasing photosynthetic quotient) which was not predicted by a previously developed simple dynamic model of photosynthesis and respiration reactions. The incorporation of developmental stages into the model allowed for the representation of this change in metabolism without adding unnecessary complexity. Developmental stages were implemented by dividing the model into two successive sub-models with independent yields. The transition between the phases was detected based on online measurements. Results showed an accurate prediction of carbon dioxide and oxygen fluxes.

  9. Dynamic model of the Earth's upper atmosphere

    NASA Technical Reports Server (NTRS)

    Slowey, J. W.

    1984-01-01

    An initial modification to the MSF/J70 Thermospheric Model, in which the variations due to sudden geomagnetic disturbances upon the Earth's upper atmospheric density structure were modeled is presented. This dynamic model of the geomagnetic variation included is an improved version of one which SAO developed from the analysis of the ESRO 4 mass spectrometer data that was incorporated in the Jacchia 1977 model. The variation with geomagnetic local time as well as with geomagnetic latitude are included, and also the effects due to disturbance of the temperature profiles in the region of energy deposition.

  10. Model Of Neural Network With Creative Dynamics

    NASA Technical Reports Server (NTRS)

    Zak, Michail; Barhen, Jacob

    1993-01-01

    Paper presents analysis of mathematical model of one-neuron/one-synapse neural network featuring coupled activation and learning dynamics and parametrical periodic excitation. Demonstrates self-programming, partly random behavior of suitable designed neural network; believed to be related to spontaneity and creativity of biological neural networks.

  11. Modeling the Hydrogen Bond within Molecular Dynamics

    ERIC Educational Resources Information Center

    Lykos, Peter

    2004-01-01

    The structure of a hydrogen bond is elucidated within the framework of molecular dynamics based on the model of Rahman and Stillinger (R-S) liquid water treatment. Thus, undergraduates are exposed to the powerful but simple use of classical mechanics to solid objects from a molecular viewpoint.

  12. VUV 157nm laser ablation of spherical particles and modelling of whispering gallery mode optical antenna structures

    SciTech Connect

    Walton, C. D.; Cockcroft, S.; Metheringham, W. J.

    2012-07-30

    We report on VUV 157nm F{sub 2} laser irradiation of CR-39 polymer substrates that have been intentionally seeded with spherical glass particles. We discuss the importance of adhesive forces for realizing spherical cavity structures by laser ablation. Strong optical absorption at 157nm in CR-39 enables precise control of pedestal height by controlling the laser fluence and the number of laser pulses. Resonant modes for free-standing spherical cavities have been calculated and we discuss briefly the potential applications for use as optical sources on-board lab-on-chip devices.

  13. Population mixture model for nonlinear telomere dynamics

    NASA Astrophysics Data System (ADS)

    Itzkovitz, Shalev; Shlush, Liran I.; Gluck, Dan; Skorecki, Karl

    2008-12-01

    Telomeres are DNA repeats protecting chromosomal ends which shorten with each cell division, eventually leading to cessation of cell growth. We present a population mixture model that predicts an exponential decrease in telomere length with time. We analytically solve the dynamics of the telomere length distribution. The model provides an excellent fit to available telomere data and accounts for the previously unexplained observation of telomere elongation following stress and bone marrow transplantation, thereby providing insight into the nature of the telomere clock.

  14. First-Principles Investigations on Thermal Conductivity and Average Ionization of CH Ablators Under Extreme Conditions

    NASA Astrophysics Data System (ADS)

    Hu, S. X.; Goncharov, V. N.; McCrory, R. L.; Skupsky, S.; Collins, L. A.; Kress, J. D.

    2015-11-01

    A plastic CH ablator (polystyrene) is often used for inertial confinement fusion (ICF) target designs. Upon intense laser or x-ray ablations, a CH ablator can be shocked to warm-dense-matter (WDM) conditions. Many-body coupling and quantum electron degeneracy are expected to play an essential role in determining the properties of such warm dense plasmas. Using ab initio methods of quantum molecular dynamics (QMD), we have performed investigations on the principal Hugoniot of a CH ablator, the first-principles equation-of-state table of CH, and its effect on ICF simulations. In this presentation, we focus on the thermal conductivity and average ionization of CH-ablators under a wide range of plasma temperatures and densities. The resulting thermal conductivity (κ) and average ionization () show large differences from the usual model predictions in the WDM regime. These results, being fitted with analytical functions of plasma density and temperature, have been incorporated into radiation -hydrodynamics codes. Their effects on the ICF implosion simulations will be presented. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944 and the Scientific Campaign 10 at LANL under Contract No. DE-AC52-06NA25396.

  15. Feature extraction for structural dynamics model validation

    SciTech Connect

    Hemez, Francois; Farrar, Charles; Park, Gyuhae; Nishio, Mayuko; Worden, Keith; Takeda, Nobuo

    2010-11-08

    This study focuses on defining and comparing response features that can be used for structural dynamics model validation studies. Features extracted from dynamic responses obtained analytically or experimentally, such as basic signal statistics, frequency spectra, and estimated time-series models, can be used to compare characteristics of structural system dynamics. By comparing those response features extracted from experimental data and numerical outputs, validation and uncertainty quantification of numerical model containing uncertain parameters can be realized. In this study, the applicability of some response features to model validation is first discussed using measured data from a simple test-bed structure and the associated numerical simulations of these experiments. issues that must be considered were sensitivity, dimensionality, type of response, and presence or absence of measurement noise in the response. Furthermore, we illustrate a comparison method of multivariate feature vectors for statistical model validation. Results show that the outlier detection technique using the Mahalanobis distance metric can be used as an effective and quantifiable technique for selecting appropriate model parameters. However, in this process, one must not only consider the sensitivity of the features being used, but also correlation of the parameters being compared.

  16. Rupture dynamics in model polymer systems.

    PubMed

    Borah, Rupam; Debnath, Pallavi

    2016-05-11

    In this paper we explore the rupture dynamics of a model polymer system to capture the microscopic mechanism during relative motion of surfaces at the single polymer level. Our model is similar to the model for friction introduced by Filippov, Klafter, and Urbakh [Filippov et al., Phys. Rev. Lett., 2004, 92, 135503]; but with an important generalization to a flexible transducer (modelled as a bead spring polymer) which is attached to a fixed rigid planar substrate by interconnecting bonds (modelled as harmonic springs), and pulled by a constant force FT. Bonds are allowed to rupture stochastically. The model is simulated, and the results for a certain set of parameters exhibit a sequential rupture mechanism resulting in rupture fronts. A mean field formalism is developed to study these rupture fronts and the possible propagating solutions for the coupled bead and bond dynamics, where the coupling excludes an exact analytical treatment. Numerical solutions to mean field equations are obtained by standard numerical techniques, and they agree well with the simulation results which show sequential rupture. Within a travelling wave formalism based on the Tanh method, we show that the velocity of the rupture front can be obtained in closed form. The derived expression for the rupture front velocity gives good agreement with the stochastic and mean field results, when the rupture is sequential, while propagating solutions for bead and bond dynamics are shown to agree under certain conditions. PMID:27087684

  17. Dynamic models for the study of frailty.

    PubMed

    Lipsitz, Lewis A

    2008-11-01

    Frailty can be viewed as resulting from the degradation of multiple interacting physiologic systems that are normally responsible for healthy adaptation to the daily demands of life. Mathematical models that can quantify alterations in the dynamics of physiologic systems and their interactions may help characterize the syndrome of frailty and enable investigators to test interventions to prevent its onset. One theoretical mathematical model reported by Varadhan et al. in this issue of the Journal represents one type of regulatory process that may become altered in frail individuals-the stimulus-response mechanism [Varadhan, R., Seplaki, C.S., Xue, Q.L., Bandeen-Roche, K., Fried, L.P. Stimulus-response paradigm for characterizing the loss of resilience in homeostatic regulation associated with frailty. Mech. Ageing Dev., this issue]. This model focuses on the timing of recovery from a single stimulus, rather than the full array of responses that might be altered in a complex dynamical system. Therefore, alternative models are needed to describe the wide variety of behaviors of physiologic systems over time and how they change with the onset of frailty. One such model, based on a simple signaling network composed of a lattice of nodes and the bi-directional connections between them, can reproduce the complex, fractal-like nature of healthy physiological processes. This model can be used to demonstrate how the degradation of signaling pathways within a physiologic system can result in the loss of complex dynamics that characterizes frailty. PMID:18930754

  18. Nonsmooth dynamics in spiking neuron models

    NASA Astrophysics Data System (ADS)

    Coombes, S.; Thul, R.; Wedgwood, K. C. A.

    2012-11-01

    Large scale studies of spiking neural networks are a key part of modern approaches to understanding the dynamics of biological neural tissue. One approach in computational neuroscience has been to consider the detailed electrophysiological properties of neurons and build vast computational compartmental models. An alternative has been to develop minimal models of spiking neurons with a reduction in the dimensionality of both parameter and variable space that facilitates more effective simulation studies. In this latter case the single neuron model of choice is often a variant of the classic integrate-and-fire model, which is described by a nonsmooth dynamical system. In this paper we review some of the more popular spiking models of this class and describe the types of spiking pattern that they can generate (ranging from tonic to burst firing). We show that a number of techniques originally developed for the study of impact oscillators are directly relevant to their analysis, particularly those for treating grazing bifurcations. Importantly we highlight one particular single neuron model, capable of generating realistic spike trains, that is both computationally cheap and analytically tractable. This is a planar nonlinear integrate-and-fire model with a piecewise linear vector field and a state dependent reset upon spiking. We call this the PWL-IF model and analyse it at both the single neuron and network level. The techniques and terminology of nonsmooth dynamical systems are used to flesh out the bifurcation structure of the single neuron model, as well as to develop the notion of Lyapunov exponents. We also show how to construct the phase response curve for this system, emphasising that techniques in mathematical neuroscience may also translate back to the field of nonsmooth dynamical systems. The stability of periodic spiking orbits is assessed using a linear stability analysis of spiking times. At the network level we consider linear coupling between voltage

  19. Condensed Antenna Structural Models for Dynamics Analysis

    NASA Technical Reports Server (NTRS)

    Levy, R.

    1985-01-01

    Condensed degree-of-freedom models are compared with large degree-of-freedom finite-element models of a representative antenna-tipping and alidade structure, for both locked and free-rotor configurations. It is shown that: (1) the effective-mass models accurately reproduce the lower-mode natural frequencies of the finite element model; (2) frequency responses for the two types of models are in agreement up to at least 16 rad/s for specific points; and (3) transient responses computed for the same points are in good agreement. It is concluded that the effective-mass model, which best represents the five lower modes of the finite-element model, is a sufficient representation of the structure for future incorporation with a total servo control structure dynamic simulation.

  20. Dynamic occupancy models for explicit colonization processes.

    PubMed

    Broms, Kristin M; Hooten, Mevin B; Johnson, Devin S; Altwegg, Res; Conquest, Loveday L

    2016-01-01

    The dynamic, multi-season occupancy model framework has become a popular tool for modeling open populations with occupancies that change over time through local colonizations and extinctions. However, few versions of the model relate these probabilities to the occupancies of neighboring sites or patches. We present a modeling framework that incorporates this information and is capable of describing a wide variety of spatiotemporal colonization and extinction processes. A key feature of the model is that it is based on a simple set of small-scale rules describing how the process evolves. The result is a dynamic process that can account for complicated large-scale features. In our model, a site is more likely to be colonized if more of its neighbors were previously occupied and if it provides more appealing environmental characteristics than its neighboring sites. Additionally, a site without occupied neighbors may also become colonized through the inclusion of a long-distance dispersal process. Although similar model specifications have been developed for epidemiological applications, ours formally accounts for detectability using the well-known occupancy modeling framework. After demonstrating the viability and potential of this new form of dynamic occupancy model in a simulation study, we use it to obtain inference for the ongoing Common Myna (Acridotheres tristis) invasion in South Africa. Our results suggest that the Common Myna continues to enlarge its distribution and its spread via short distance movement, rather than long-distance dispersal. Overall, this new modeling framework provides a powerful tool for managers examining the drivers of colonization including short- vs. long-distance dispersal, habitat quality, and distance from source populations. PMID:27008788

  1. Dynamic occupancy models for explicit colonization processes

    USGS Publications Warehouse

    Broms, Kristin M.; Hooten, Mevin B.; Johnson, Devin S.; Altwegg, Res; Conquest, Loveday

    2016-01-01

    The dynamic, multi-season occupancy model framework has become a popular tool for modeling open populations with occupancies that change over time through local colonizations and extinctions. However, few versions of the model relate these probabilities to the occupancies of neighboring sites or patches. We present a modeling framework that incorporates this information and is capable of describing a wide variety of spatiotemporal colonization and extinction processes. A key feature of the model is that it is based on a simple set of small-scale rules describing how the process evolves. The result is a dynamic process that can account for complicated large-scale features. In our model, a site is more likely to be colonized if more of its neighbors were previously occupied and if it provides more appealing environmental characteristics than its neighboring sites. Additionally, a site without occupied neighbors may also become colonized through the inclusion of a long-distance dispersal process. Although similar model specifications have been developed for epidemiological applications, ours formally accounts for detectability using the well-known occupancy modeling framework. After demonstrating the viability and potential of this new form of dynamic occupancy model in a simulation study, we use it to obtain inference for the ongoing Common Myna (Acridotheres tristis) invasion in South Africa. Our results suggest that the Common Myna continues to enlarge its distribution and its spread via short distance movement, rather than long-distance dispersal. Overall, this new modeling framework provides a powerful tool for managers examining the drivers of colonization including short- vs. long-distance dispersal, habitat quality, and distance from source populations.

  2. Direct modeling for computational fluid dynamics

    NASA Astrophysics Data System (ADS)

    Xu, Kun

    2015-06-01

    All fluid dynamic equations are valid under their modeling scales, such as the particle mean free path and mean collision time scale of the Boltzmann equation and the hydrodynamic scale of the Navier-Stokes (NS) equations. The current computational fluid dynamics (CFD) focuses on the numerical solution of partial differential equations (PDEs), and its aim is to get the accurate solution of these governing equations. Under such a CFD practice, it is hard to develop a unified scheme that covers flow physics from kinetic to hydrodynamic scales continuously because there is no such governing equation which could make a smooth transition from the Boltzmann to the NS modeling. The study of fluid dynamics needs to go beyond the traditional numerical partial differential equations. The emerging engineering applications, such as air-vehicle design for near-space flight and flow and heat transfer in micro-devices, do require further expansion of the concept of gas dynamics to a larger domain of physical reality, rather than the traditional distinguishable governing equations. At the current stage, the non-equilibrium flow physics has not yet been well explored or clearly understood due to the lack of appropriate tools. Unfortunately, under the current numerical PDE approach, it is hard to develop such a meaningful tool due to the absence of valid PDEs. In order to construct multiscale and multiphysics simulation methods similar to the modeling process of constructing the Boltzmann or the NS governing equations, the development of a numerical algorithm should be based on the first principle of physical modeling. In this paper, instead of following the traditional numerical PDE path, we introduce direct modeling as a principle for CFD algorithm development. Since all computations are conducted in a discretized space with limited cell resolution, the flow physics to be modeled has to be done in the mesh size and time step scales. Here, the CFD is more or less a direct

  3. Synthesis and characterization of gold graphene composite with dyes as model substrates for decolorization: a surfactant free laser ablation approach.

    PubMed

    Sai Siddhardha, R S; Lakshman Kumar, V; Kaniyoor, Adarsh; Sai Muthukumar, V; Ramaprabhu, S; Podila, Ramakrishna; Rao, A M; Ramamurthy, Sai Sathish

    2014-12-10

    A facile surfactant free laser ablation mediated synthesis (LAMS) of gold-graphene composite is reported here. The material was characterized using transmission electron microscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, powdered X-ray diffraction, Raman spectroscopy, Zeta potential measurements and UV-Visible spectroscopic techniques. The as-synthesized gold-graphene composite was effectively utilized as catalyst for decolorization of 4 important textile and laser dyes. The integration of gold nanoparticles (AuNPs) with high surface area graphene has enhanced the catalytic activity of AuNPs. This enhanced activity is attributed to the synergistic interplay of pristine gold's electronic relay and π-π stacking of graphene with the dyes. This is evident when the Rhodamine B (RB) reduction rate of the composite is nearly twice faster than that of commercial citrate capped AuNPs of similar size. In case of Methylene blue (MB) the rate of reduction is 17,000 times faster than uncatalyzed reaction. This synthetic method opens door to laser ablation based fabrication of metal catalysts on graphene for improved performance without the aid of linkers and surfactants.

  4. Synthesis and characterization of gold graphene composite with dyes as model substrates for decolorization: A surfactant free laser ablation approach

    NASA Astrophysics Data System (ADS)

    Sai Siddhardha, R. S.; Lakshman Kumar, V.; Kaniyoor, Adarsh; Sai Muthukumar, V.; Ramaprabhu, S.; Podila, Ramakrishna; Rao, A. M.; Ramamurthy, Sai Sathish

    2014-12-01

    A facile surfactant free laser ablation mediated synthesis (LAMS) of gold-graphene composite is reported here. The material was characterized using transmission electron microscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, powdered X-ray diffraction, Raman spectroscopy, Zeta potential measurements and UV-Visible spectroscopic techniques. The as-synthesized gold-graphene composite was effectively utilized as catalyst for decolorization of 4 important textile and laser dyes. The integration of gold nanoparticles (AuNPs) with high surface area graphene has enhanced the catalytic activity of AuNPs. This enhanced activity is attributed to the synergistic interplay of pristine gold's electronic relay and π-π stacking of graphene with the dyes. This is evident when the Rhodamine B (RB) reduction rate of the composite is nearly twice faster than that of commercial citrate capped AuNPs of similar size. In case of Methylene blue (MB) the rate of reduction is 17,000 times faster than uncatalyzed reaction. This synthetic method opens door to laser ablation based fabrication of metal catalysts on graphene for improved performance without the aid of linkers and surfactants.

  5. Femtosecond laser ablation of the stapes

    PubMed Central

    McCaughey, Ryan G.; Sun, Hui; Rothholtz, Vanessa S.; Juhasz, Tibor; Wong, Brian J. F.

    2014-01-01

    A femtosecond laser, normally used for LASIK eye surgery, is used to perforate cadaveric human stapes. The thermal side effects of bone ablation are measured with a thermocouple in an inner ear model and are found to be within acceptable limits for inner ear surgery. Stress and acoustic events, recorded with piezoelectric film and a microphone, respectively, are found to be negligible. Optical microscopy, scanning electron microscopy, and optical coherence tomography are used to confirm the precision of the ablation craters and lack of damage to the surrounding tissue. Ablation is compared to that from an Er:YAG laser, the current laser of choice for stapedotomy, and is found to be superior. Ultra-short-pulsed lasers offer a precise and efficient ablation of the stapes, with minimal thermal and negligible mechanical and acoustic damage. They are, therefore, ideal for stapedotomy operations. PMID:19405768

  6. Dynamics of macroautophagy: Modeling and oscillatory behavior

    NASA Astrophysics Data System (ADS)

    Han, Kyungreem; Kwon, Hyun Woong; Kang, Hyuk; Kim, Jinwoong; Lee, Myung-Shik; Choi, M. Y.

    2012-02-01

    We propose a model for macroautophagy and study the resulting dynamics of autophagy in a system isolated from its extra-cellular environment. It is found that the intracellular concentrations of autophagosomes and autolysosomes display oscillations with their own natural frequencies. Such oscillatory behaviors, which are interrelated to the dynamics of intracellular ATP, amino acids, and proteins, are consistent with the very recent biological observations. Implications of this theoretical study of autophagy are discussed, with regard to the possibility of guiding molecular studies of autophagy.

  7. Dynamic modeling and simulation of planetary rovers

    NASA Astrophysics Data System (ADS)

    Lindemann, Randel A.

    1992-02-01

    This paper documents a preliminary study into the dynamic modeling and computer simulation of wheeled surface vehicles. The research centered on the feasibility of using commercially available multibody dynamics codes running on engineering workstations to perform the analysis. The results indicated that physically representative vehicle mechanics can be modeled and simulated in state-of-the-art Computer Aided Engineering environments, but at excessive cost in modeling and computation time. The results lead to the recommendation for the development of an efficient rover mobility-specific software system. This system would be used for vehicle design and simulation in planetary environments; controls prototyping, design, and testing; as well as local navigation simulation and expectation planning.

  8. Methodology for Uncertainty Analysis of Dynamic Computational Toxicology Models

    EPA Science Inventory

    The task of quantifying the uncertainty in both parameter estimates and model predictions has become more important with the increased use of dynamic computational toxicology models by the EPA. Dynamic toxicological models include physiologically-based pharmacokinetic (PBPK) mode...

  9. The dynamic modelling of a slotted test section

    NASA Technical Reports Server (NTRS)

    Gumas, G.

    1979-01-01

    A mathematical model of the wind tunnel dynamics was developed. The modelling techniques were restricted to the use of one dimensional unsteady flow. The dynamic characteristics of slotted test section incorporated into the model are presented.

  10. Global dynamic modeling of a transmission system

    NASA Technical Reports Server (NTRS)

    Choy, F. K.; Qian, W.

    1993-01-01

    The work performed on global dynamic simulation and noise correlation of gear transmission systems at the University of Akron is outlined. The objective is to develop a comprehensive procedure to simulate the dynamics of the gear transmission system coupled with the effects of gear box vibrations. The developed numerical model is benchmarked with results from experimental tests at NASA Lewis Research Center. The modal synthesis approach is used to develop the global transient vibration analysis procedure used in the model. Modal dynamic characteristics of the rotor-gear-bearing system are calculated by the matrix transfer method while those of the gear box are evaluated by the finite element method (NASTRAN). A three-dimensional, axial-lateral coupled bearing model is used to couple the rotor vibrations with the gear box motion. The vibrations between the individual rotor systems are coupled through the nonlinear gear mesh interactions. The global equations of motion are solved in modal coordinates and the transient vibration of the system is evaluated by a variable time-stepping integration scheme. The relationship between housing vibration and resulting noise of the gear transmission system is generated by linear transfer functions using experimental data. A nonlinear relationship of the noise components to the fundamental mesh frequency is developed using the hypercoherence function. The numerically simulated vibrations and predicted noise of the gear transmission system are compared with the experimental results from the gear noise test rig at NASA Lewis Research Center. Results of the comparison indicate that the global dynamic model developed can accurately simulate the dynamics of a gear transmission system.

  11. Global dynamic modeling of a transmission system

    NASA Astrophysics Data System (ADS)

    Choy, F. K.; Qian, W.

    1993-04-01

    The work performed on global dynamic simulation and noise correlation of gear transmission systems at the University of Akron is outlined. The objective is to develop a comprehensive procedure to simulate the dynamics of the gear transmission system coupled with the effects of gear box vibrations. The developed numerical model is benchmarked with results from experimental tests at NASA Lewis Research Center. The modal synthesis approach is used to develop the global transient vibration analysis procedure used in the model. Modal dynamic characteristics of the rotor-gear-bearing system are calculated by the matrix transfer method while those of the gear box are evaluated by the finite element method (NASTRAN). A three-dimensional, axial-lateral coupled bearing model is used to couple the rotor vibrations with the gear box motion. The vibrations between the individual rotor systems are coupled through the nonlinear gear mesh interactions. The global equations of motion are solved in modal coordinates and the transient vibration of the system is evaluated by a variable time-stepping integration scheme. The relationship between housing vibration and resulting noise of the gear transmission system is generated by linear transfer functions using experimental data. A nonlinear relationship of the noise components to the fundamental mesh frequency is developed using the hypercoherence function. The numerically simulated vibrations and predicted noise of the gear transmission system are compared with the experimental results from the gear noise test rig at NASA Lewis Research Center. Results of the comparison indicate that the global dynamic model developed can accurately simulate the dynamics of a gear transmission system.

  12. Development of a dynamic thermal model process

    SciTech Connect

    Smith, F. R.

    1996-04-01

    A dynamic electrical-thermal modeling simulation technique was developed to allow up-front design of thermal and electronic packaging with a high degree of accuracy and confidence. We are developing a hybrid multichip module output driver which controls with power MOSFET driver circuits. These MOSFET circuits will dissipate from 13 to 26 watts per driver in a physical package less than two square inches. The power dissipation plus an operating temperature range of -55{degrees} C to 100{degrees} C makes an accurate thermal package design critical. The project goal was to develop a simulation process to dynamically model the electrical/thermal characteristics of the power MOSFETS using the SABER analog simulator and the ABAQUS finite element simulator. SABER would simulate the electrical characteristics of the multi-chip module design while co-simulation is being done with ABAQUS simulating the solid model thermal characteristics of the MOSFET package. The dynamic parameters, MOSFET power and chip temperature, would be actively passed between simulators to effect a coupled simulator modelling technique. The project required a development of a SABER late for the analog ASIC controller circuit, a dynamic electrical/thermal template for the IRF150 and IRF9130 power MOSFETs, a solid model of the multi-chip module package, FORTRAN code to handle I/Q between and HP755 workstation and SABER, and I/O between CRAY J90 computer and ABAQUS. The simulation model was certified by measured electrical characteristics of the circuits and real time thermal imaging of the output multichip module.

  13. Subject-specific four-dimensional liver motion modeling based on registration of dynamic MRI.

    PubMed

    Noorda, Yolanda H; Bartels, Lambertus W; Viergever, Max A; Pluim, Josien P W

    2016-01-01

    Magnetic resonance-guided high intensity focused ultrasound treatment of the liver is a promising noninvasive technique for ablation of liver lesions. For the technique to be used in clinical practice, however, the issue of liver motion needs to be addressed. A subject-specific four-dimensional liver motion model is presented that is created based on registration of dynamically acquired magnetic resonance data. This model can be used for predicting the tumor motion trajectory for treatment planning and to indicate the tumor position for treatment guidance. The performance of the model was evaluated on a dynamic scan series that was not used to build the model. The method achieved an average Dice coefficient of 0.93 between the predicted and actual liver profiles and an average vessel misalignment of 3.0 mm. The model performed robustly, with a small variation in the results per subject. The results demonstrate the potential of the model to be used for MRI-guided treatment of liver lesions. Furthermore, the model can possibly be applied in other image-guided therapies, for instance radiotherapy of the liver. PMID:27493981

  14. Polarizable water model for Dissipative Particle Dynamics

    NASA Astrophysics Data System (ADS)

    Pivkin, Igor; Peter, Emanuel

    2015-11-01

    Dissipative Particle Dynamics (DPD) is an efficient particle-based method for modeling mesoscopic behavior of fluid systems. DPD forces conserve the momentum resulting in a correct description of hydrodynamic interactions. Polarizability has been introduced into some coarse-grained particle-based simulation methods; however it has not been done with DPD before. We developed a new polarizable coarse-grained water model for DPD, which employs long-range electrostatics and Drude oscillators. In this talk, we will present the model and its applications in simulations of membrane systems, where polarization effects play an essential role.

  15. Fluid-dynamical model for antisurfactants

    NASA Astrophysics Data System (ADS)

    Conn, Justin J. A.; Duffy, Brian R.; Pritchard, David; Wilson, Stephen K.; Halling, Peter J.; Sefiane, Khellil

    2016-04-01

    We construct a fluid-dynamical model for the flow of a solution with a free surface at which surface tension acts. This model can describe both classical surfactants, which decrease the surface tension of the solution relative to that of the pure solvent, and antisurfactants (such as many salts when added to water, and small amounts of water when added to alcohol) which increase it. We demonstrate the utility of the model by considering the linear stability of an infinitely deep layer of initially quiescent fluid. In particular, we predict the occurrence of an instability driven by surface-tension gradients, which occurs for antisurfactant, but not for surfactant, solutions.

  16. Informations in Models of Evolutionary Dynamics

    NASA Astrophysics Data System (ADS)

    Rivoire, Olivier

    2016-03-01

    Biological organisms adapt to changes by processing informations from different sources, most notably from their ancestors and from their environment. We review an approach to quantify these informations by analyzing mathematical models of evolutionary dynamics and show how explicit results are obtained for a solvable subclass of these models. In several limits, the results coincide with those obtained in studies of information processing for communication, gambling or thermodynamics. In the most general case, however, information processing by biological populations shows unique features that motivate the analysis of specific models.

  17. Overview of the GRC Stirling Convertor System Dynamic Model

    NASA Technical Reports Server (NTRS)

    Lewandowski, Edward J.; Regan, Timothy F.

    2004-01-01

    A Stirling Convertor System Dynamic Model has been developed at the Glenn Research Center for controls, dynamics, and systems development of free-piston convertor power systems. It models the Stirling cycle thermodynamics, heat flow, gas, mechanical, and mounting dynamics, the linear alternator, and the controller. The model's scope extends from the thermal energy input to thermal, mechanical dynamics, and electrical energy out, allowing one to study complex system interactions among subsystems. The model is a non-linear time-domain model containing sub-cycle dynamics, allowing it to simulate transient and dynamic phenomena that other models cannot. The model details and capability are discussed.

  18. Laser ablation of dyes

    NASA Astrophysics Data System (ADS)

    Späth, M.; Stuke, M.

    1992-01-01

    High density 50 μs pulses of the UV dyes PPF, POPOP and BBO and of two dyes in the visible region, Xanthen N92 and Fluorol 7GA were generated by laser ablation. Dye powders were pressed with 7800 kp/cm 2 in round pellets which were ablated by exposure to KrF excimer laser radiation (248 nm) at a fluence of 100 mJ/cm 2. The ablation cloud was optically activated with a XeCl excimer laser. Its fluorescence spectrum was measured and was identified as a dye vapour fluorescence spectrum by comparison to conventional dye solution and dye vapour spectra. The dye cloud is not deflected in an electric field (10 6 V/m). By changing the delay time between the ablation laser and the focused activation laser, the velocity distribution of the ablated dye was measured. Its maximum is at 600 m/s for PPF. Knowing the thickness of the ablated dye layer per shot (300 Å) and the size of the ablation cloud (pictures of a video camera), one can estimate the maximum density of the dye in the gas pulse to be 10 -5 mol/ l in the range of concentration of lasing dyes. However, no lasing was observed up to now.

  19. Tumor Ablation and Nanotechnology

    PubMed Central

    Manthe, Rachel L.; Foy, Susan P.; Krishnamurthy, Nishanth; Sharma, Blanka; Labhasetwar, Vinod

    2010-01-01

    Next to surgical resection, tumor ablation is a commonly used intervention in the treatment of solid tumors. Tumor ablation methods include thermal therapies, photodynamic therapy, and reactive oxygen species (ROS) producing agents. Thermal therapies induce tumor cell death via thermal energy and include radiofrequency, microwave, high intensity focused ultrasound, and cryoablation. Photodynamic therapy and ROS producing agents cause increased oxidative stress in tumor cells leading to apoptosis. While these therapies are safe and viable alternatives when resection of malignancies is not feasible, they do have associated limitations that prevent their widespread use in clinical applications. To improve the efficacy of these treatments, nanoparticles are being studied in combination with nonsurgical ablation regimens. In addition to better thermal effect on tumor ablation, nanoparticles can deliver anticancer therapeutics that show synergistic anti-tumor effect in the presence of heat and can also be imaged to achieve precision in therapy. Understanding the molecular mechanism of nanoparticle-mediated tumor ablation could further help engineer nanoparticles of appropriate composition and properties to synergize the ablation effect. This review aims to explore the various types of nonsurgical tumor ablation methods currently used in cancer treatment and potential improvements by nanotechnology applications. PMID:20866097

  20. 5D model for accurate representation and visualization of dynamic cardiac structures

    NASA Astrophysics Data System (ADS)

    Lin, Wei-te; Robb, Richard A.

    2000-05-01

    Accurate cardiac modeling is challenging due to the intricate structure and complex contraction patterns of myocardial tissues. Fast imaging techniques can provide 4D structural information acquired as a sequence of 3D images throughout the cardiac cycle. To mode. The beating heart, we created a physics-based surface model that deforms between successive time point in the cardiac cycle. 3D images of canine hearts were acquired during one complete cardiac cycle using the DSR and the EBCT. The left ventricle of the first time point is reconstructed as a triangular mesh. A mass-spring physics-based deformable mode,, which can expand and shrink with local contraction and stretching forces distributed in an anatomically accurate simulation of cardiac motion, is applied to the initial mesh and allows the initial mesh to deform to fit the left ventricle in successive time increments of the sequence. The resulting 4D model can be interactively transformed and displayed with associated regional electrical activity mapped onto anatomic surfaces, producing a 5D model, which faithfully exhibits regional cardiac contraction and relaxation patterns over the entire heart. The model faithfully represents structural changes throughout the cardiac cycle. Such models provide the framework for minimizing the number of time points required to usefully depict regional motion of myocardium and allow quantitative assessment of regional myocardial motion. The electrical activation mapping provides spatial and temporal correlation within the cardiac cycle. In procedures which as intra-cardiac catheter ablation, visualization of the dynamic model can be used to accurately localize the foci of myocardial arrhythmias and guide positioning of catheters for optimal ablation.

  1. Five challenges in modelling interacting strain dynamics.

    PubMed

    Wikramaratna, Paul S; Kucharski, Adam; Gupta, Sunetra; Andreasen, Viggo; McLean, Angela R; Gog, Julia R

    2015-03-01

    Population epidemiological models where hosts can be infected sequentially by different strains have the potential to help us understand many important diseases. Researchers have in recent years started to develop and use such models, but the extra layer of complexity from multiple strains brings with it many technical challenges. It is therefore hard to build models which have realistic assumptions yet are tractable. Here we outline some of the main challenges in this area. First we begin with the fundamental question of how to translate from complex small-scale dynamics within a host to useful population models. Next we consider the nature of so-called "strain space". We describe two key types of host heterogeneities, and explain how models could help generate a better understanding of their effects. Finally, for diseases with many strains, we consider the challenge of modelling how immunity accumulates over multiple exposures.

  2. Structural system identification: Structural dynamics model validation

    SciTech Connect

    Red-Horse, J.R.

    1997-04-01

    Structural system identification is concerned with the development of systematic procedures and tools for developing predictive analytical models based on a physical structure`s dynamic response characteristics. It is a multidisciplinary process that involves the ability (1) to define high fidelity physics-based analysis models, (2) to acquire accurate test-derived information for physical specimens using diagnostic experiments, (3) to validate the numerical simulation model by reconciling differences that inevitably exist between the analysis model and the experimental data, and (4) to quantify uncertainties in the final system models and subsequent numerical simulations. The goal of this project was to develop structural system identification techniques and software suitable for both research and production applications in code and model validation.

  3. Dynamic alignment models for neural coding.

    PubMed

    Kollmorgen, Sepp; Hahnloser, Richard H R

    2014-03-01

    Recently, there have been remarkable advances in modeling the relationships between the sensory environment, neuronal responses, and behavior. However, most models cannot encompass variable stimulus-response relationships such as varying response latencies and state or context dependence of the neural code. Here, we consider response modeling as a dynamic alignment problem and model stimulus and response jointly by a mixed pair hidden Markov model (MPH). In MPHs, multiple stimulus-response relationships (e.g., receptive fields) are represented by different states or groups of states in a Markov chain. Each stimulus-response relationship features temporal flexibility, allowing modeling of variable response latencies, including noisy ones. We derive algorithms for learning of MPH parameters and for inference of spike response probabilities. We show that some linear-nonlinear Poisson cascade (LNP) models are a special case of MPHs. We demonstrate the efficiency and usefulness of MPHs in simulations of both jittered and switching spike responses to white noise and natural stimuli. Furthermore, we apply MPHs to extracellular single and multi-unit data recorded in cortical brain areas of singing birds to showcase a novel method for estimating response lag distributions. MPHs allow simultaneous estimation of receptive fields, latency statistics, and hidden state dynamics and so can help to uncover complex stimulus response relationships that are subject to variable timing and involve diverse neural codes. PMID:24625448

  4. Dynamic Alignment Models for Neural Coding

    PubMed Central

    Kollmorgen, Sepp; Hahnloser, Richard H. R.

    2014-01-01

    Recently, there have been remarkable advances in modeling the relationships between the sensory environment, neuronal responses, and behavior. However, most models cannot encompass variable stimulus-response relationships such as varying response latencies and state or context dependence of the neural code. Here, we consider response modeling as a dynamic alignment problem and model stimulus and response jointly by a mixed pair hidden Markov model (MPH). In MPHs, multiple stimulus-response relationships (e.g., receptive fields) are represented by different states or groups of states in a Markov chain. Each stimulus-response relationship features temporal flexibility, allowing modeling of variable response latencies, including noisy ones. We derive algorithms for learning of MPH parameters and for inference of spike response probabilities. We show that some linear-nonlinear Poisson cascade (LNP) models are a special case of MPHs. We demonstrate the efficiency and usefulness of MPHs in simulations of both jittered and switching spike responses to white noise and natural stimuli. Furthermore, we apply MPHs to extracellular single and multi-unit data recorded in cortical brain areas of singing birds to showcase a novel method for estimating response lag distributions. MPHs allow simultaneous estimation of receptive fields, latency statistics, and hidden state dynamics and so can help to uncover complex stimulus response relationships that are subject to variable timing and involve diverse neural codes. PMID:24625448

  5. Interval modeling of dynamics for multibody systems

    NASA Astrophysics Data System (ADS)

    Auer, Ekaterina

    2007-02-01

    Modeling of multibody systems is an important though demanding field of application for interval arithmetic. Interval modeling of dynamics is particularly challenging, not least because of the differential equations which have to be solved in the process. Most modeling tools transform these equations into a (non-autonomous) initial value problem, interval algorithms for solving of which are known. The challenge then consists in finding interfaces between these algorithms and the modeling tools. This includes choosing between "symbolic" and "numerical" modeling environments, transforming the usually non-autonomous resulting system into an autonomous one, ensuring conformity of the new interval version to the old numerical, etc. In this paper, we focus on modeling multibody systems' dynamics with the interval extension of the "numerical" environment MOBILE, discuss the techniques which make the uniform treatment of interval and non-interval modeling easier, comment on the wrapping effect, and give reasons for our choice of MOBILE by comparing the results achieved with its help with those obtained by analogous symbolic tools.

  6. Cellular automata modelling of biomolecular networks dynamics.

    PubMed

    Bonchev, D; Thomas, S; Apte, A; Kier, L B

    2010-01-01

    The modelling of biological systems dynamics is traditionally performed by ordinary differential equations (ODEs). When dealing with intracellular networks of genes, proteins and metabolites, however, this approach is hindered by network complexity and the lack of experimental kinetic parameters. This opened the field for other modelling techniques, such as cellular automata (CA) and agent-based modelling (ABM). This article reviews this emerging field of studies on network dynamics in molecular biology. The basics of the CA technique are discussed along with an extensive list of related software and websites. The application of CA to networks of biochemical reactions is exemplified in detail by the case studies of the mitogen-activated protein kinase (MAPK) signalling pathway, the FAS-ligand (FASL)-induced and Bcl-2-related apoptosis. The potential of the CA method to model basic pathways patterns, to identify ways to control pathway dynamics and to help in generating strategies to fight with cancer is demonstrated. The different line of CA applications presented includes the search for the best-performing network motifs, an analysis of importance for effective intracellular signalling and pathway cross-talk. PMID:20373215

  7. Dynamic Modeling of an Evapotranspiration Cap

    SciTech Connect

    Jacob J. Jacobson; Steven Piet; Rafael Soto; Gerald Sehlke; Harold Heydt; John Visser

    2005-10-01

    The U.S. Department of Energy is scheduled to design and install hundreds of landfill caps/barriers over the next several decades and these caps will have a design life expectancy of up to 1,000 years. Other landfill caps with 30 year design lifetimes are reaching the end of their original design life; the changes to these caps need to be understood to provide a basis for lifetime extension. Defining the attributes that make a successful cap (one that isolates the waste from the environment) is crucial to these efforts. Because cap systems such as landfill caps are dynamic in nature, it is impossible to understand, monitor, and update lifetime predictions without understanding the dynamics of cap degradation, which is most often due to multiple interdependent factors rather than isolated independent events. In an attempt to understand the dynamics of cap degradation, a computer model using system dynamics is being developed to capture the complex behavior of an evapotranspiration cap. The specific objectives of this project are to capture the dynamic, nonlinear feedback loop structures underlying an evapotranspiration cap and, through computer simulation, gain a better understanding of long-term behavior, influencing factors, and, ultimately, long-term cap performance.

  8. Dynamical Study of Femtosecond-Laser-Ablated Liquid-Aluminum Nanoparticles Using Spatiotemporally Resolved X-Ray-Absorption Fine-Structure Spectroscopy

    SciTech Connect

    Oguri, Katsuya; Okano, Yasuaki; Nishikawa, Tadashi; Nakano, Hidetoshi

    2007-10-19

    We study the temperature evolution of aluminum nanoparticles generated by femtosecond laser ablation with spatiotemporally resolved x-ray-absorption fine-structure spectroscopy. We successfully identify the nanoparticles based on the L-edge absorption fine structure of the ablation plume in combination with the dependence of the edge structure on the irradiation intensity and the expansion velocity of the plume. In particular, we show that the lattice temperature of the nanoparticles is estimated from the L-edge slope, and that its spatial dependence reflects the cooling of the nanoparticles during plume expansion. The results reveal that the emitted nanoparticles travel in a vacuum as a condensed liquid phase with a lattice temperature of about 2500 to 4200 K in the early stage of plume expansion.

  9. Modeling the dynamic characteristics of pneumatic muscle.

    PubMed

    Reynolds, D B; Repperger, D W; Phillips, C A; Bandry, G

    2003-03-01

    A pneumatic muscle (PM) system was studied to determine whether a three-element model could describe its dynamics. As far as the authors are aware, this model has not been used to describe the dynamics of PM. A new phenomenological model consists of a contractile (force-generating) element, spring element, and damping element in parallel. The PM system was investigated using an apparatus that allowed precise and accurate actuation pressure (P) control by a linear servo-valve. Length change of the PM was measured by a linear potentiometer. Spring and damping element functions of P were determined by a static perturbation method at several constant P values. These results indicate that at constant P, PM behaves as a spring and damper in parallel. The contractile element function of P was determined by the response to a step input in P, using values of spring and damping elements from the perturbation study. The study showed that the resulting coefficient functions of the three-element model describe the dynamic response to the step input of P accurately, indicating that the static perturbation results can be applied to the dynamic case. This model is further validated by accurately predicting the contraction response to a triangular P waveform. All three elements have pressure-dependent coefficients for pressure P in the range 207 < or = P < or = 621 kPa (30 < or = P < or = 90 psi). Studies with a step decrease in P (relaxation of the PM) indicate that the damping element coefficient is smaller during relaxation than contraction.

  10. Modelling Holocene peatland and permafrost dynamics with the LPJ-GUESS dynamic vegetation model

    NASA Astrophysics Data System (ADS)

    Chaudhary, Nitin; Miller, Paul A.; Smith, Benjamin

    2016-04-01

    Dynamic global vegetation models (DGVMs) are an important platform to study past, present and future vegetation patterns together with associated biogeochemical cycles and climate feedbacks (e.g. Sitch et al. 2008, Smith et al. 2001). However, very few attempts have been made to simulate peatlands using DGVMs (Kleinen et al. 2012, Tang et al. 2015, Wania et al. 2009a). In the present study, we have improved the peatland dynamics in the state-of-the-art dynamic vegetation model (LPJ-GUESS) in order to understand the long-term evolution of northern peatland ecosystems and to assess the effect of changing climate on peatland carbon balance. We combined a dynamic multi-layer approach (Frolking et al. 2010, Hilbert et al. 2000) with soil freezing-thawing functionality (Ekici et al. 2015, Wania et al. 2009a) in LPJ-GUESS. The new model is named LPJ-GUESS Peatland (LPJ-GUESS-P) (Chaudhary et al. in prep). The model was calibrated and tested at the sub-arctic mire in Stordalen, Sweden, and the model was able to capture the reported long-term vegetation dynamics and peat accumulation patterns in the mire (Kokfelt et al. 2010). For evaluation, the model was run at 13 grid points across a north to south transect in Europe. The modelled peat accumulation values were found to be consistent with the published data for each grid point (Loisel et al. 2014). Finally, a series of additional experiments were carried out to investigate the vulnerability of high-latitude peatlands to climate change. We find that the Stordalen mire will sequester more carbon in the future due to milder and wetter climate conditions, longer growing seasons, and the carbon fertilization effect. References: - Chaudhary et al. (in prep.). Modelling Holocene peatland and permafrost dynamics with the LPJ-GUESS dynamic vegetation model - Ekici A, et al. 2015. Site-level model intercomparison of high latitude and high altitude soil thermal dynamics in tundra and barren landscapes. The Cryosphere 9: 1343

  11. Navigation Systems for Ablation

    PubMed Central

    Wood, B. J.; Kruecker, J.; Abi-Jaoudeh, N; Locklin, J.; Levy, E.; Xu, S.; Solbiati, L.; Kapoor, A.; Amalou, H.; Venkatesan, A.

    2010-01-01

    Navigation systems, devices and intra-procedural software are changing the way we practice interventional oncology. Prior to the development of precision navigation tools integrated with imaging systems, thermal ablation of hard-to-image lesions was highly dependent upon operator experience, spatial skills, and estimation of positron emission tomography-avid or arterial-phase targets. Numerous navigation systems for ablation bring the opportunity for standardization and accuracy that extends our ability to use imaging feedback during procedures. Existing systems and techniques are reviewed, and specific clinical applications for ablation are discussed to better define how these novel technologies address specific clinical needs, and fit into clinical practice. PMID:20656236

  12. Modelling the mechanoreceptor’s dynamic behaviour

    PubMed Central

    Song, Zhuoyi; Banks, Robert W; Bewick, Guy S

    2015-01-01

    All sensory receptors adapt, i.e. they constantly adjust their sensitivity to external stimuli to match the current demands of the natural environment. Electrophysiological responses of sensory receptors from widely different modalities seem to exhibit common features related to adaptation, and these features can be used to examine the underlying sensory transduction mechanisms. Among the principal senses, mechanosensation remains the least understood at the cellular level. To gain greater insights into mechanosensory signalling, we investigated if mechanosensation displayed adaptive dynamics that could be explained by similar biophysical mechanisms in other sensory modalities. To do this, we adapted a fly photoreceptor model to describe the primary transduction process for a stretch-sensitive mechanoreceptor, taking into account the viscoelastic properties of the accessory muscle fibres and the biophysical properties of known mechanosensitive channels (MSCs). The model’s output is in remarkable agreement with the electrical properties of a primary ending in an isolated decapsulated spindle; ramp-and-hold stretch evokes a characteristic pattern of potential change, consisting of a large dynamic depolarization during the ramp phase and a smaller static depolarization during the hold phase. The initial dynamic component is likely to be caused by a combination of the mechanical properties of the muscle fibres and a refractory state in the MSCs. Consistent with the literature, the current model predicts that the dynamic component is due to a rapid stress increase during the ramp. More novel predictions from the model are the mechanisms to explain the initial peak in the dynamic component. At the onset of the ramp, all MSCs are sensitive to external stimuli, but as they become refractory (inactivated), fewer MSCs are able to respond to the continuous stretch, causing a sharp decrease after the peak response. The same mechanism could contribute a faster component in

  13. Effect of Current Rise-time on the Formation of Precursor Structures and Mass Ablation Rate in Cylindrical Wire Array Z-Pinches

    SciTech Connect

    Bott, S. C.; Eshaq, Y.; Ueda, U.; Haas, D. M.; Beg, F. N.; Hammer, D. A.; Kusse, B.; Greenly, J.; Shelkovenko, T. A.; Pikuz, S. A.; Blesener, I. C.; McBride, R. D.; Douglass, J. D.; Bell, K.; Knapp, P.; Chittenden, J. P.; Lebedev, S. V.; Bland, S. N.; Hall, G. N.; Suzuki, F. A.

    2009-01-21

    We present the first study to directly compare the mass ablation rates of cylindrical wire arrays as a function of the current rise-rate. Formation of the precursor column is investigated on both the MAPGIE (1 MA, 250 ns) and COBRA (1 MA, 100 ns) generators, and results are used to infer the change in the mass ablation rate induced by the rise-rate of the drive current. Laser shadowography, gated XUV imaging and x-ray diodes are used to compare the dynamical behavior both generators, and x-pinch radiography and XUV spectroscopy and provide density evolution and temperature measurements respectively. Results are compared to predictions from an analytical scaling model based on a fixed ablation rate, and the close correlation achieved suggests that the effective ablation velocity is not a strong function of the current rise rate.

  14. Dynamical Causal Modeling from a Quantum Dynamical Perspective

    SciTech Connect

    Demiralp, Emre; Demiralp, Metin

    2010-09-30

    Recent research suggests that any set of first order linear vector ODEs can be converted to a set of specific vector ODEs adhering to what we have called ''Quantum Harmonical Form (QHF)''. QHF has been developed using a virtual quantum multi harmonic oscillator system where mass and force constants are considered to be time variant and the Hamiltonian is defined as a conic structure over positions and momenta to conserve the Hermiticity. As described in previous works, the conversion to QHF requires the matrix coefficient of the first set of ODEs to be a normal matrix. In this paper, this limitation is circumvented using a space extension approach expanding the potential applicability of this method. Overall, conversion to QHF allows the investigation of a set of ODEs using mathematical tools available to the investigation of the physical concepts underlying quantum harmonic oscillators. The utility of QHF in the context of dynamical systems and dynamical causal modeling in behavioral and cognitive neuroscience is briefly discussed.

  15. Dynamical Causal Modeling from a Quantum Dynamical Perspective

    NASA Astrophysics Data System (ADS)

    Demiralp, Emre; Demiralp, Metin

    2010-09-01

    Recent research suggests that any set of first order linear vector ODEs can be converted to a set of specific vector ODEs adhering to what we have called "Quantum Harmonical Form (QHF)". QHF has been developed using a virtual quantum multi harmonic oscillator system where mass and force constants are considered to be time variant and the Hamiltonian is defined as a conic structure over positions and momenta to conserve the Hermiticity. As described in previous works, the conversion to QHF requires the matrix coefficient of the first set of ODEs to be a normal matrix. In this paper, this limitation is circumvented using a space extension approach expanding the potential applicability of this method. Overall, conversion to QHF allows the investigation of a set of ODEs using mathematical tools available to the investigation of the physical concepts underlying quantum harmonic oscillators. The utility of QHF in the context of dynamical systems and dynamical causal modeling in behavioral and cognitive neuroscience is briefly discussed.

  16. The dynamic radiation environment assimilation model (DREAM)

    SciTech Connect

    Reeves, Geoffrey D; Koller, Josef; Tokar, Robert L; Chen, Yue; Henderson, Michael G; Friedel, Reiner H

    2010-01-01

    The Dynamic Radiation Environment Assimilation Model (DREAM) is a 3-year effort sponsored by the US Department of Energy to provide global, retrospective, or real-time specification of the natural and potential nuclear radiation environments. The DREAM model uses Kalman filtering techniques that combine the strengths of new physical models of the radiation belts with electron observations from long-term satellite systems such as GPS and geosynchronous systems. DREAM includes a physics model for the production and long-term evolution of artificial radiation belts from high altitude nuclear explosions. DREAM has been validated against satellites in arbitrary orbits and consistently produces more accurate results than existing models. Tools for user-specific applications and graphical displays are in beta testing and a real-time version of DREAM has been in continuous operation since November 2009.

  17. Dynamic mesh for TCAD modeling with ECORCE

    NASA Astrophysics Data System (ADS)

    Michez, A.; Boch, J.; Touboul, A.; Saigné, F.

    2016-08-01

    Mesh generation for TCAD modeling is challenging. Because densities of carriers can change by several orders of magnitude in thin areas, a significant change of the solution can be observed for two very similar meshes. The mesh must be defined at best to minimize this change. To address this issue, a criterion based on polynomial interpolation on adjacent nodes is proposed that adjusts accurately the mesh to the gradients of Degrees of Freedom. Furthermore, a dynamic mesh that follows changes of DF in DC and transient mode is a powerful tool for TCAD users. But, in transient modeling, adding nodes to a mesh induces oscillations in the solution that appears as spikes at the current collected at the contacts. This paper proposes two schemes that solve this problem. Examples show that using these techniques, the dynamic mesh generator of the TCAD tool ECORCE handle semiconductors devices in DC and transient mode.

  18. Modeling of dynamic fragmentation in brittle materials

    NASA Astrophysics Data System (ADS)

    Miller, Olga

    Fragmentation of brittle materials under high rates of loading is commonly encountered in materials processing and under impact loading conditions. Theoretical models intended to correlate the features of dynamic fragmentation have been suggested during the past few years with the goal of providing a rational basis for prediction of fragment sizes. In this thesis, a new model based on the dynamics of the process is developed. In this model, the spatial distribution and strength variation representative of flaws in real brittle materials are taken into account. The model captures the competition between rising mean stress in a brittle material due to an imposed high strain rate and falling mean stress due to loss of compliance. The model is studied computationally through an adaptation of a concept introduced by Xu and Needleman (1994). The deformable body is first divided into many small regions. Then, the mechanical behavior of the material is characterized by two constitutive relations, a volumetric constitutive relationship between stress and strain within the small continuous regions and a cohesive surface constitutive relationship between traction and displacement discontinuity across the cohesive surfaces between the small regions. These surfaces provide prospective fracture paths. Numerical experiments were conducted for a system with initial and boundary conditions similar to those invoked in the simple energy balance models, in order to provide a basis for comparison. It is found that, these models lead to estimates of fragment size which are an order of magnitude larger than those obtained by a more detailed calculation. The differences indicate that the simple analytical models, which deal with the onset of fragmentation but not its evolution, are inadequate as a basis for a complete description of a dynamic fragmentation process. The computational model is then adapted to interpret experimental observations on the increasing energy dissipation for

  19. A Model for Nonstationary Market Dynamics with Nontrivial Dynamical Scaling

    NASA Astrophysics Data System (ADS)

    Liu, Min; Bassler, Kevin E.

    2008-03-01

    In a recent empirical analysis of the Euro/Dollar exchange rate [Bassler, et al., PNAS 104, 17287 (2007)] it was found that during certain periods of the day the market returns scale with Hurst exponents H that are significantly different from 1/2. In some of these periods it is less than 1/2, while in others it is greater than 1/2. In this talk we will propose a possible origin for this behavior and other stylized market facts, including short time negative autocorrelations of returns, in terms of a nonstationary compound Poisson process with a time-dependent intensity rate function that results from a changing bid-ask spread in the microscopic market. The model correctly describes the dynamic scaling behavior of a simple reaction-diffusion model of a limit-order book. That model, like the Euro/Dollar exchange rate, has nonstationary return increments and a Hurst exponent H not equal to 1/2.