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Sample records for modeling orifice pulse

  1. Modeling Orifice Pulse Tube Coolers

    NASA Technical Reports Server (NTRS)

    Roach, Kittel P.; Roach, P. R.; Lee, J. M.; Kashani, A.; McCreight, Craig R. (Technical Monitor)

    1996-01-01

    We have developed a calculational model that treats all the components of an orifice pulse tube cooler. We base our analysis on 1-dimensional thermodynamic equations for the regenerator and we assume that all mass flows, pressure oscillations and temperature oscillations are small and sinusoidal. Non-linear pressure drop effects are included in the regenerator to account for finite pressure amplitude effects. The resulting mass flows and pressures are matched at the boundaries with the other components of the cooler: compressor, aftercooler, cold heat exchanger, pulse tube, hot heat exchanger, orifice and reservoir. The results of the calculation are oscillating pressures, mass flows and enthalpy flows in the main components of the cooler. By comparing with the calculations of other available models, we show that our model is very similar to REGEN 3 from NIST and DeltaE from Los Alamos National Lab. Our model is much easier to use than other available models because of its simple graphical interface and the fact that no guesses are required for the operating pressures or mass flows. In addition, the model only requires a few minutes of running time allowing many parameters to be optimized in a reasonable time. A version of the model is available for use over the World Wide Web at http://irtek.arc.nasa.gov. Future enhancements include adding a bypass orifice and including second order terms in steady mass streaming and steady heat transfer. A two-dimensional anelastic approximation of the fluid equations will be used as the basis for the latter analysis. Preliminary results are given in dimensionless numbers appropriate for oscillating compressible flows. The model shows how transverse heat transfer reduces enthalpy flow, particularly for small pulse tubes. The model also clearly shows mass recirculation in the open tube on the order of the tube length. They result from the higher order Reynolds stresses. An interesting result of the linearized approach is that the

  2. Development and experimental test of an analytical model of the orifice pulse tube refrigerator

    NASA Technical Reports Server (NTRS)

    Storch, Peter J.; Radebaugh, Ray

    1988-01-01

    An analytical model for the orifice pulse tube is developed, in which the system is described in terms of average enthalpy flow with such simplifying assumptions as an ideal gas and sinusoidal pressure variation. Phasor analysis is used to represent temperature, pressure, and mass-flow rate waves in vector form. The model predictions, namely, that the refrigeration power of a pulse-tube refrigerator is proportional to the average pressure, the pulse frequency, the mass-flow ratio, and the square of the dynamic pressure ratio, were verified by experimental measurements. It was found that, as a result of the simplifying assumptions, the magnitudes of the refrigeration power predicted by the model were between three and five times greater than experimental values.

  3. Ideal orifice pulse tube refrigerator performance

    NASA Technical Reports Server (NTRS)

    Kittel, P.

    1992-01-01

    The recent development of orifice pulse tube refrigerators has raised questions as to what limits their ultimate performance. Using an analogy to the Stirling cycle refrigerator, the efficiency (cooling power per unit input power) of an ideal orifice pulse tube refrigerator is shown to be T1/T0, the ratio of the cold temperature to the hot temperature.

  4. A small, single stage orifice pulse tube cryocooler demonstration

    NASA Technical Reports Server (NTRS)

    Hendricks, John B.

    1990-01-01

    This final report summarizes and presents the analytical and experimental progress in the present effort. The principal objective of this effort was the demonstration of a 0.25 Watt, 80 Kelvin orifice pulse tube refrigerator. The experimental apparatus is described. The design of a partially optimized pulse tube refrigerator is included. The refrigerator demonstrates an ultimate temperature of 77 K, has a projected cooling power of 0.18 Watts at 80 K, and has a measured cooling power of 1 Watt at 97 K, with an electrical efficiency of 250 Watts/Watt, much better than previous pulse tube refrigerators. A model of the pulse tube refrigerator that provides estimates of pressure ratio and mass flow within the pulse tube refrigerator, based on component physical characteristics is included. A model of a pulse tube operation based on generalized analysis which is adequate to support local optimization of existing designs is included. A model of regenerator performance based on an analogy to counterflow heat exchangers is included.

  5. Fluid mechanical model of the acoustic impedance of small orifices

    NASA Technical Reports Server (NTRS)

    Hersh, A. S.; Rogers, T.

    1975-01-01

    A fluid mechanical model of the acoustic behavior of small orifices is presented which predicts orifice impedance as a function of incident sound pressure level, frequency, and orifice geometry. Agreement between predicted and measured values (in both water and air) of orifice impedance is excellent. The model shows that (1) the acoustic flow in the immediate neighborhood of the orifice can be modelled as a locally spherical flow, (2) within this near field, the flow is, to a first approximation, unsteady and incompressible, and (3) at very low sound pressure levels, the orifice viscous resistance is directly related to the effect of boundary-layer displacement along the walls containing the orifice, and the orifice reactance is directly related to the inertia of the oscillating flow in the orifice neighborhood.-

  6. Fluid mechanical model of the acoustic impedance of small orifices

    NASA Technical Reports Server (NTRS)

    Hersh, A. S.; Rogers, T.

    1976-01-01

    A fluid mechanical model of the acoustic behavior of small orifices is presented which predicts orifice resistance and reactance as a function of incident sound pressure level, frequency, and orifice geometry. Agreement between predicted and measured values is excellent. The model shows the following: (1) The acoustic flow in immediate neighborhood of the orifice can be modeled as a locally spherical flow. Within this near field, the flow is, to a first approximation, unsteady and incompressible. (2) At very low sound pressure levels, the orifice viscous resistance is directly related to the effect of boundary-layer displacement along the walls containing the orifice, and the orifice reactance is directly related to the inertia of the oscillating flow in the neighborhood of the orifice. (3) For large values of the incident acoustic pressure, the impedance is dominated by nonlinear jet-like effects. (4) For low values of the pressure, the resistance and reactance are roughly equal.

  7. Numerical modeling of flow through orifice meters

    NASA Astrophysics Data System (ADS)

    Sheikholesiami, M. Z.; Patel, B. R.

    1988-03-01

    Numerical modeling is performed for turbulent flow through orifice meters using Creare's computer program FLUENT. FLUENT solves the time averaged Navier-Stokes equations in 2-D and 3-D Cartesian or cylindrical coordinates. Turbulence is simulated using a two equation k-epsilon or algebraic stress turbulence model. It is shown that an 80 x 60 grid distribution is sufficient to resolve the flow field around the orifice. The variations in discharge coefficient are studied as a result of variation in beta ratio, Reynolds number, upstream and downstream boundary conditions, pipe surface roughness, and upstream swirl. The effects of beta ratio and Reynolds number on the discharge coefficient are shown to be similar to the experimental data. It is also shown that the surface roughness can increase the discharge coefficient by about 0.7 percent for the range of roughness heights encountered in practice. The numerical modeling approach would be most effective if it is combined with a systematic experimental program that can supply the necessary boundary conditions. It is recommended that numerical modeling be used for the study of other flow meters.

  8. Method and apparatus for fine tuning an orifice pulse tube refrigerator

    DOEpatents

    Swift, Gregory W.; Wollan, John J.

    2003-12-23

    An orifice pulse tube refrigerator uses flow resistance, compliance, and inertance components connected to a pulse tube for establishing a phase relationship between oscillating pressure and oscillating velocity in the pulse tube. A temperature regulating system heats or cools a working gas in at least one of the flow resistance and inertance components. A temperature control system is connected to the temperature regulating system for controlling the temperature of the working gas in the at least one of the flow resistance and inertance components and maintains a control temperature that is indicative of a desired temporal phase relationship.

  9. The influence of gas velocity on surface heat pumping for the orifice pulse tube refrigerator

    NASA Technical Reports Server (NTRS)

    Lee, J. M.; Dill, H. R.

    1990-01-01

    The basic pulse tube refrigerator produces cooling by a mechanism known as surface heat pumping. Cyclical compression and expansion of a gas within an enclosed tube produces large temperature gradients. The purpose of the tube is to act as 'nodal regenerator'. Heat is stored at node positions along the tube wall and is transported between nodes by moving gas parcels. This process gives rise to refrigeration, with hot temperatures at the closed end and cold temperatures at the open end. Unfortunately, much of the available refrigeration is not realized because the closed end of the basic pulse tube restricts gas movement - gas at the extreme temperatures does not come in contact with the heat exchangers. The orifice pulse tube overcomes this limitation by using a valve and surge volume assembly at the warm, closed end. This allows for a residual gas velocity to remain present during the heat transfer process, thereby permitting more gas to exchange heat at the heat exchangers. This paper describes the pulse tube as a nodal regenerator and the effect residual gas velocity has on the heat transfer mechanism of the orifice pulse tube.

  10. Frequency-domain methods for modeling a nonlinear acoustic orifice

    NASA Astrophysics Data System (ADS)

    Egolf, David P.; Murphy, William J.; Franks, John R.; Kirlin, R. Lynn

    2002-11-01

    This presentation describes frequency-domain methods for simulating transmission loss across a single orifice mounted in an acoustic waveguide. The work was a preamble to research involving earplugs containing one or more orifices. Simulation methods included direct Fourier transformation, linearization about an operating point, and Volterra series. They were applied to an electric-circuit analog of the acoustic system containing the orifice. The orifice itself was characterized by an empirical expression for nonlinear impedance obtained by fitting curves to experimental resistance and reactance data reported by other authors. Their data-collection procedures required the impedance expression presented herein to be properly labeled as a describing function, a quantity well known in the nonlinear control systems literature. Results of the computer simulations were compared to experimental transmission-loss data. For a single-tone input sound pressure, the computer code accurately predicted the output fundamental (i.e., without harmonics). For a broadband input, the simulated output was less accurate, but acceptable. Levels of the sound-pressure input ranged from 60 to 160 dB. [Work supported by the National Institute for Occupational Safety and Health, Cincinnati, OH, through a research associateship granted the first author by the National Research Council.] a)Currently on leave at National Institute for Occupational Safety and Health, Cincinnati, OH.

  11. Visualization of Orifice Flow with Measurement-integrated Simulation Using a Turbulent Model

    NASA Astrophysics Data System (ADS)

    Nakao, Mitsuhiro; Kawashima, Kenji; Kagawa, Toshiharu

    Measurement-integrated (MI) simulation is a numerical simulation in which experimental results are fed back to the simulation. The calculated values become closer to the experimental values. In this paper, MI simulation using a standard k-ε model is proposed and applied it to steady airflows passing an orifice plate in a pipeline. The upstream corner tap pressure in simulation is compensated by using proportional controller or proportional-integral controller. The signal is fed back to the axial velocity control volume in vena contract. The effectiveness of the method was evaluated compared with the experimental results at downstream of orifice. The calculation time of proposed MI simulation is significantly reduced compared with ordinary simulation analysis.

  12. Localisation and direction of mitral regurgitant flow in mitral orifice studied with combined use of ultrasonic pulsed Doppler technique and two dimensional echocardiography.

    PubMed Central

    Miyatake, K; Nimura, Y; Sakakibara, H; Kinoshita, N; Okamoto, M; Nagata, S; Kawazoe, K; Fujita, T

    1982-01-01

    Regurgitant flow was analysed in 40 cases of mitral regurgitation, using combined ultrasonic pulsed Doppler technique and two dimensional echocardiography. Abnormal Doppler signals indicative of mitral regurgitant flow were detected in reference to the two dimensional image of the long axis view of the heart and the short axis view at the level of the mitral orifice. The overall direction of regurgitant flow into the left atrium was clearly seen in 28 of 40 cases, and the localisation of regurgitant flow in the mitral orifice in 38 cases. In cases with mitral valve prolapse of the anterior leaflet or posterior leaflet the regurgitant flow was directed posteriorly or anteriorly, respectively. The prolapse occurred at the anterolateral commissure or posteromedial commissure and resulted in regurgitant flow located near the anterolateral commissure or posteromedial commissure of the mitral orifice, respectively. In cases with rheumatic mitral regurgitation the regurgitant flow is usually towards the central portion of the left atrium and is sited in the mid-part of the orifice. The Doppler findings were consistent with left ventriculography and surgical findings. The ultrasonic pulsed Doppler technique combined with two dimensional echocardiography is useful for non-invasive analysis and preoperative assessment of mitral regurgitation. Images PMID:7138708

  13. Numerical modeling of flow through orifice meters. Topical report, July 1986-August 1987

    SciTech Connect

    Sheikholeslami, M.Z.; Patel, B.R.

    1988-03-01

    Numerical modeling is performed for turbulent flow through orifice meters using Creare's computer program FLUENT. FLUENT solves the time averaged Navier-Stokes equations in 2D/3D Cartesian or cylindrical coordinates. Turbulence is simulated using a two-equation k-epsilon or algebraic stress-turbulence model. It is shown that an 80x60 grid distribution is sufficient to resolve the flow field around the orifice. The variations in discharge coefficient are studied as a result of variation in beta ratio, Reynolds number, upstream and downstream boundary conditions, pipe surface roughness, and upstream swirl. The effects of beta ratio and Reynolds number on the discharge coefficient are shown to be similar to the experimental data. It is also shown that the surface roughness can increase the discharge coefficient by about 0.7% for the range of roughness heights encountered in practice. The numerical-modeling approach would be most effective if it is combined with a systematic experimental program that can supply the necessary boundary conditions. It is recommended that numerical modeling be used for the study of other flow meters.

  14. Cavitation in an orifice flow

    NASA Astrophysics Data System (ADS)

    Dabiri, S.; Sirignano, W. A.; Joseph, D. D.

    2007-07-01

    The purpose of this study is to identify the potential locations for cavitation induced by total stress on the flow of a liquid through an orifice of an atomizer. A numerical simulation of two-phase incompressible flow is conducted in an axisymmetric geometry of the orifice for Reynolds numbers between 100 and 2000. The orifice has a rounded upstream corner and a sharp downstream corner with length-to-diameter ratio between 0.1 and 5. The total stress including viscous stress and pressure has been calculated in the flow field and, from there, the maximum principal stress is found. The total-stress criterion for cavitation is applied to find the regions where cavitation is likely to occur and compared with those of the traditional pressure criterion. Results show that the viscous stress has significant effects on cavitation. The effect of geometry and occurrence of hydraulic flip in the orifice on the total stress are studied. The Navier-Stokes equations are solved numerically using a finite-volume method and a boundary-fitted orthogonal grid that comes from the streamlines and potential lines of an axisymmetric equipotential flow in the same geometry. A level-set formulation is used to track the interface and model the surface tension.

  15. Pulsed Plasma Accelerator Modeling

    NASA Technical Reports Server (NTRS)

    Goodman, M.; Kazeminezhad, F.; Owens, T.

    2009-01-01

    This report presents the main results of the modeling task of the PPA project. The objective of this task is to make major progress towards developing a new computational tool with new capabilities for simulating cylindrically symmetric 2.5 dimensional (2.5 D) PPA's. This tool may be used for designing, optimizing, and understanding the operation of PPA s and other pulsed power devices. The foundation for this task is the 2-D, cylindrically symmetric, magnetohydrodynamic (MHD) code PCAPPS (Princeton Code for Advanced Plasma Propulsion Simulation). PCAPPS was originally developed by Sankaran (2001, 2005) to model Lithium Lorentz Force Accelerators (LLFA's), which are electrode based devices, and are typically operated in continuous magnetic field to the model, and implementing a first principles, self-consistent algorithm to couple the plasma and power circuit that drives the plasma dynamics.

  16. Systemic Inflammatory Response After Natural Orifice Translumenal Surgery: Transvaginal Cholecystectomy in a Porcine Model

    PubMed Central

    Fan, Joe K. M.; Tong, Daniel K. H.; HO, David W. Y.; Luk, John; Law, Simon

    2009-01-01

    Objective: We analyzed circulating TNF-α and IL-6 to determine systemic inflammatory responses associated with transvaginal cholecystectomy in a porcine model. Methods: Six female pigs were used for a survival study after transvaginal cholecystectomy (NOTES group) using endoscopic submucosal dissection (ESD) instruments and a single-channel endoscope. Blood was drawn preoperatively and 24 hours and 48 hours postoperatively. Four pigs were used as controls. In addition, laparoscopic cholecystectomy was performed in 2 pigs for laparoscopic control. Results: In all 6 pigs in the NOTES group, no major intraoperative complications occurred. No significant differences were found between control, laparoscopic, and NOTES groups in terms of preoperative IL-6 level (P=0.897) and at 24 hours (P=0.790), and 48 hours postoperatively (P=0.945). Similarly, there was no significant difference in mean preoperative (P=0.349) and mean day 2 postoperative TNF-α levels (P=0.11). But a significant increase in day 1 postoperative TNF-α levels in the laparoscopic group compared with that in the control and NOTES groups was observed (P=0.049). One limitation of our study is that the sample size was relatively small. Conclusion: NOTES is safe in animal models in terms of anatomical and cellular level changes with minimal systemic inflammatory host responses elicited. Further study needs to be carried out in humans before NOTES can be recommended for routine use. PMID:19366533

  17. Effect of grazing flow on the acoustic impedance of Helmholtz resonators consisting of single and clustered orifices

    NASA Technical Reports Server (NTRS)

    Hersh, A. S.; Walker, B.; Bucka, M.

    1978-01-01

    A semiempirical fluid mechanical model is presented which predicts impedance of a Helmholtz resonator consisting of a single cavity-backed orifice as a function of grazing flow speed, boundary-layer thickness, incident sound amplitude and frequency, and resonator geometry. The incident and cavity sound fields are connected in terms of an orifice discharge coefficient. The effect of multiple orifices was studied experimentally. Interaction between orifices is important only for orifices aligned parallel to the grazing flow. Resistance was virtually independent of both orifice relative spacing and number. Reactance was found to be quite dependent upon orifice spacing but insensitive to the number of orifices.

  18. Pulse Detonation Engine Modeled

    NASA Technical Reports Server (NTRS)

    Paxson, Daniel E.

    2001-01-01

    Pulse Detonation Engine Technology is currently being investigated at Glenn for both airbreathing and rocket propulsion applications. The potential for both mechanical simplicity and high efficiency due to the inherent near-constant-volume combustion process, may make Pulse Detonation Engines (PDE's) well suited for a number of mission profiles. Assessment of PDE cycles requires a simulation capability that is both fast and accurate. It should capture the essential physics of the system, yet run at speeds that allow parametric analysis. A quasi-one-dimensional, computational-fluid-dynamics-based simulation has been developed that may meet these requirements. The Euler equations of mass, momentum, and energy have been used along with a single reactive species transport equation, and submodels to account for dominant loss mechanisms (e.g., viscous losses, heat transfer, and valving) to successfully simulate PDE cycles. A high-resolution numerical integration scheme was chosen to capture the discontinuities associated with detonation, and robust boundary condition procedures were incorporated to accommodate flow reversals that may arise during a given cycle. The accompanying graphs compare experimentally measured and computed performance over a range of operating conditions for a particular PDE. Experimental data were supplied by Fred Schauer and Jeff Stutrud from the Air Force Research Laboratory at Wright-Patterson AFB and by Royce Bradley from Innovative Scientific Solutions, Inc. The left graph shows thrust and specific impulse, Isp, as functions of equivalence ratio for a PDE cycle in which the tube is completely filled with a detonable hydrogen/air mixture. The right graph shows thrust and specific impulse as functions of the fraction of the tube that is filled with a stoichiometric mixture of hydrogen and air. For both figures, the operating frequency was 16 Hz. The agreement between measured and computed values is quite good, both in terms of trend and

  19. High Pressure Water Stripping Using Multi-Orifice Nozzles

    NASA Technical Reports Server (NTRS)

    Hoppe, David

    1999-01-01

    The use of multi-orifice rotary nozzles greatly increases the speed and stripping effectiveness of high pressure water blasting systems, but also greatly increases the complexity of selecting and optimizing the operating parameters. The rotational speed of the nozzle must be coupled with its transverse velocity as it passes across the surface of the substrate being stripped. The radial and angular positions of each orifice must be included in the analysis of the nozzle configuration. Orifices at the outer edge of the nozzle head move at a faster rate than the orifices located near the center. The energy transmitted to the surface from the impact force of the water stream from an outer orifice is therefore spread over a larger area than energy from an inner orifice. Utilizing a larger diameter orifice in the outer radial positions increases the total energy transmitted from the outer orifice to compensate for the wider distribution of energy. The total flow rate from the combination of all orifices must be monitored and should be kept below the pump capacity while choosing orifice to insert in each position. The energy distribution from the orifice pattern is further complicated since the rotary path of all the orifices in the nozzle head pass through the center section. All orifices contribute to the stripping in the center of the path while only the outer most orifice contributes to the stripping at the edge of the nozzle. Additional orifices contribute to the stripping from the outer edge toward the center section. With all these parameters to configure and each parameter change affecting the others, a computer model was developed to track and coordinate these parameters. The computer simulation graphically indicates the cumulative affect from each parameter selected. The result from the proper choices in parameters is a well designed, highly efficient stripping system. A poorly chosen set of parameters will cause the nozzle to strip aggressively in some areas

  20. Active Control of Liner Impedance by Varying Perforate Orifice Geometry

    NASA Technical Reports Server (NTRS)

    Ahuji, K. K.; Gaeta, R. J., Jr.

    2000-01-01

    The present work explored the feasibility of controlling the acoustic impedance of a resonant type acoustic liner. This was accomplished by translating one perforate over another of the same porosity creating a totally new perforate that had an intermediate porosity. This type of adjustable perforate created a variable orifice perforate whose orifices were non-circular. The key objective of the present study was to quantify, the degree of attenuation control that can be achieved by applying such a concept to the buried septum in a two-degree-of-freedom (2DOF) acoustic liner. An additional objective was to examine the adequacy of the existing impedance models to explain the behavior of the unique orifice shapes that result from the proposed silding perforate concept. Different orifice shapes with equivalent area were also examined to determine if highly non-circular orifices had a significant impact on the impedance.

  1. Balanced Orifice Plate

    NASA Technical Reports Server (NTRS)

    Kelley, Anthony R. (Inventor); Buskirk, Paul D. (Inventor)

    2006-01-01

    An orifice plate for use in a conduit through which fluid flows is defined by a central circular region having a radius R, and a ring-shaped region surrounding the central circular region. The ring-shaped region has holes formed therethrough with those holes centered at each radius R thereof satisfying a relationship A(sub R)=al(X(sub R)V(sub R)(sup b)) where A(sub R) is a sum of areas of those holes having centers at radius R, X(sub R) is a flow coefficient at radius R, V(sub R) is a velocity of the fluid that is to flow through the conduit at radius R, b is a constant selected to make at least one process variable (associated with the fluid that is to flow through the conduit) approximately equal at each radius R, and a is a constant that is equal to (X(sub R)A(sub R)V(sub R)(sup b)) at each radius R.

  2. High Pressure Water Stripping Using Multi-Orifice Nozzles

    NASA Technical Reports Server (NTRS)

    Hoppe, David T.

    1998-01-01

    The use of multi-orifice rotary nozzles not only increases the speed and stripping effectiveness of high pressure water blasting systems, but also greatly increases the complexity of selecting and optimizing the operating parameters. The rotational speed of the nozzle must be coupled with the transverse velocity of the nozzle as it passes across the surface of the substrate being stripped. The radial and angular positions of each orifice must be included in the analysis of the nozzle configuration. Since orifices at the outer edge of the nozzle head move at a faster rate than the orifice located near the center, the energy impact force of the water stream from the outer orifice is spread over a larger area than the water streams from the inner orifice. Utilizing a larger diameter orifice in the outer radial positions increases the energy impact to compensate for its wider force distribution. The total flow rate from the combination of orifices must be monitored and kept below the pump capacity while choosing an orifice to insert in each position. The energy distribution from the orifice pattern is further complicated since the rotary path of all orifices in the nozzle head pass through the center section, contributing to the stripping in this area while only the outer most orifice contributes to the stripping in the shell area at the extreme outside edge of the nozzle. From t he outer most shell to the center section, more orifices contribute to the stripping in each progressively reduced diameter shell. With all these parameters to configure and each parameter change affecting the others, a computer model was developed to track and coordinate these parameters. The computer simulation responds by graphically indicating the cumulative affect from each parameter selected. The results from the proper choices in parameters is a well designed, highly efficient stripping system. A poorly chosen set of parameters will cause the nozzle to strip aggressively in some areas

  3. Pulse height model for deuterated scintillation detectors

    NASA Astrophysics Data System (ADS)

    Wang, Haitang; Enqvist, Andreas

    2015-12-01

    An analytical model of light pulse height distribution for finite deuterated scintillation detectors is created using the impulse approximation. Particularly, the energy distribution of a scattered neutron is calculated based on an existing collision probability scheme for general cylindrical shaped detectors considering double differential cross-sections. The light pulse height distribution is analytically and numerically calculated by convoluting collision sequences with the light output function for an EJ-315 detector from our measurements completed at Ohio University. The model provides a good description of collision histories capturing transferred neutron energy in deuterium-based scintillation materials. The resulting light pulse height distribution details pulse compositions and their corresponding contributions. It shows that probabilities of neutron collision with carbon and deuterium nuclei are comparable, however the light pulse amplitude due to collisions with carbon nuclei is small and mainly located at the lower region of the light pulse distribution axis. The model can explore those neutron interaction events that generate pulses near or below a threshold that would be imposed in measurements. A comparison is made between the light pulse height distributions given by the analytical model and measurements. It reveals a significant probability of a neutron generating a small light pulse due to collisions with carbon nuclei when compared to larger light pulse generated by collisions involving deuterium nuclei. This model is beneficial to understand responses of scintillation materials and pulse compositions, as well as nuclei information extraction from recorded pulses.

  4. Successful balloon dilatation of both orifices in a case of double-orifice mitral valve with severe rheumatic stenosis.

    PubMed

    Nath, Ranjit Kumar; Soni, Dheeraj Kumar

    2016-08-01

    A 24-year-old female patient presented to us with progressive dyspnea on exertion for last three year. She was not a known case of rheumatic heart disease. Her physical examination showed regular pulse and her blood pressure was 100/76 mm Hg. Cardiac palpation showed grade 3 parasternal heave and auscultation revelled an accentuated first heart sound, loud P2 and mid-diastolic long rumbling murmur at apex and pansystolic murmur of tricuspid regurgitation at lower left sterna border. Chest X-ray showed evidence of grade 3 pulmonary venous congestion. Transthoracic and transesophageal two-dimensional echocardiography revealed a double-orifice mitral valve of complete bridge type at the leaflet level. Both orifice sizes were unequal, with the anterolateral orifice being smaller than its counterpart. There was moderate subvalvular fusion and both commisures were fused. Color doppler examination showed two separate mitral diastolic flows with mean gradients of 22 mm and 20 mm of Hg, respectively. There was no mitral regurgitation and no left atrial or appendage clot was seen by transesophageal echocardiography. Transseptal puncture was done by the modified fluoroscopic method. Posteromedial orifice was crossed with a 24 mm Inoue balloon and dilated using the stepwise dilation technique. Anterolateral orifice was not crossed by Inuoe balloon after multiple attempts. A TYSHAK (NuMAD Canada Inc.) balloon (16 × 40mm) was taken over the wire and inflated successfully across the anterolateral orifice with the help of transthoracic echocardiography guidance. Mean gradient become 9 and 8 mm across the medial and lateral orifice. Patient was discharged in stable condition after two day. © 2015 Wiley Periodicals, Inc. PMID:26389694

  5. Natural orifice transluminal endoscopic wedge hepatic resection with a water-jet hybrid knife in a non-survival porcine model

    PubMed Central

    Shi, Hong; Jiang, Sheng-Jun; Li, Bin; Fu, Deng-Ke; Xin, Pei; Wang, Yong-Guang

    2011-01-01

    AIM: To explore the feasibility of a water-jet hybrid knife to facilitate wedge hepatic resection using a natural orifice transluminal endoscopic surgery (NOTES) approach in a non-survival porcine model. METHODS: The Erbe Jet2 water-jet system allows a needleless, tissue-selective hydro-dissection with a pre-selected pressure. Using this system, wedge hepatic resection was performed through three natural routes (trans-anal, trans-vaginal and trans-umbilical) in three female pigs weighing 35 kg under general anesthesia. Entry into the peritoneal cavity was via a 15-mm incision using a hook knife. The targeted liver segment was marked by an APC probe, followed by wedge hepatic resection performed using a water-jet hybrid knife with the aid of a 4-mm transparent distance soft cap mounted onto the tip of the endoscope for holding up the desired plane. The exposed vascular and ductal structures were clipped with Endoclips. Hemostasis was applied to the bleeding cut edges of the liver parenchyma by electrocautery. After the procedure, the incision site was left open, and the animal was euthanized followed by necropsy. RESULTS: Using the Erbe Jet2 water-jet system, trans-anal and trans-vaginal wedge hepatic resection was successfully performed in two pigs without laparoscopic assistance. Trans-umbilical attempt failed due to an unstable operating platform. The incision for peritoneal entry took 1 min, and about 2 h was spent on excision of the liver tissue. The intra-operative blood loss ranged from 100 to 250 mL. Microscopically, the hydro-dissections were relatively precise and gentle, preserving most vessels. CONCLUSION: The Erbe Jet2 water-jet system can safely accomplish non-anatomic wedge hepatic resection in NOTES, which deserves further studies to shorten the dissection time. PMID:21412502

  6. Influence of Geometry and Flow Variation on Jet Mixing and NO Formation in a Model Staged Combustor Mixer with Eight Orifices

    NASA Technical Reports Server (NTRS)

    Samuelsen, G. S.; Sowa, W. A.; Hatch, M. S.

    1996-01-01

    A series of non-reacting parametric experiments was conducted to investigate the effect of geometric and flow variations on mixing of cold jets in an axis-symmetric, heated cross flow. The confined, cylindrical geometries tested represent the quick mix region of a Rich-Burn/Quick-Mix/Lean-Burn (RQL) combustor. The experiments show that orifice geometry and jet to mainstream momentum-flux ratio significantly impact the mixing characteristic of jets in a cylindrical cross stream. A computational code was used to extrapolate the results of the non-reacting experiments to reacting conditions in order to examine the nitric oxide (NO) formation potential of the configurations examined. The results show that the rate of NO formation is highest immediately downstream of the injection plane. For a given momentum-flux ratio, the orifice geometry that mixes effectively in both the immediate vicinity of the injection plane, and in the wall regions at downstream locations, has the potential to produce the lowest NO emissions. The results suggest that further study may not necessarily lead to a universal guideline for designing a low NO mixer. Instead, an assessment of each application may be required to determine the optimum combination of momentum-flux ratio and orifice geometry to minimize NO formation. Experiments at reacting conditions are needed to verify the present results.

  7. Modeling pulse characteristics in Xenon with NEST

    NASA Astrophysics Data System (ADS)

    Mock, J.; Barry, N.; Kazkaz, K.; Stolp, D.; Szydagis, M.; Tripathi, M.; Uvarov, S.; Woods, M.; Walsh, N.

    2014-04-01

    A comprehensive model for describing the characteristics of pulsed signals, generated by particle interactions in xenon detectors, is presented. An emphasis is laid on two-phase time projection chambers, but the models presented are also applicable to single phase detectors. In order to simulate the pulse shape due to primary scintillation light, the effects of the ratio of singlet and triplet dimer state populations, as well as their corresponding decay times, and the recombination time are incorporated into the model. In a two phase time projection chamber, when simulating the pulse caused by electroluminescence light, the ionization electron mean free path in gas, the drift velocity, singlet and triplet decay times, diffusion constants, and the electron trapping time, have been implemented. This modeling has been incorporated into a complete software package, which realistically simulates the expected pulse shapes for these types of detectors.

  8. A model for pulse jet fabric filters.

    PubMed

    Ju, J; Chiu, M S; Tien, C

    2000-04-01

    A new model for pulse jet fabric filtration is proposed. In contrast to the earlier model of Ravin and Humphries, which was formulated on the steady state assumption, the present study is aimed at developing a predictive capability for both transient and steady state operations, taking into account the compression effect of filter cakes. The model's relative simplicity allows frequent updating of the model parameter values, thus improving the accuracy of predictions. As a result, the model is particularly useful in developing control algorithms and designing controllers of pulse jet fabric filtration systems. PMID:10786012

  9. Hollow Cathode With Multiple Radial Orifices

    NASA Technical Reports Server (NTRS)

    Brophy, John R.

    1992-01-01

    Improved hollow cathode serving as source of electrons has multiple radial orifices instead of single axial orifice. Distributes ion current more smoothly, over larger area. Prototype of high-current cathodes for ion engines in spacecraft. On Earth, cathodes used in large-diameter ion sources for industrial processing of materials. Radial orientation of orifices in new design causes current to be dispersed radially in vicinity of cathode. Advantageous where desireable to produce plasma more nearly uniform over wider region around cathode.

  10. Effect of mitral orifice shape on intra-ventricular filling fluid dynamics

    NASA Astrophysics Data System (ADS)

    Okafor, Ikechukwu; Angirish, Yagna; Yoganathan, Ajit; Santhanakrishnan, Arvind

    2013-11-01

    The natural geometry of the mitral orifice is D-shaped. However, most current designs of prosthetic valves employ O-shaped orifice geometry. The goal of this study was to compare the effect of geometrical modification between the D and O orifice on the intra-ventricular fluid dynamics during diastolic filling. The different mitral orifice geometries were incorporated into an in vitro left heart simulator consisting of a flexible-walled anatomical left ventricle (LV) physical model enclosed in an acrylic housing. Physiological flow rates and pressures were obtained via tuning systemic resistance and compliance elements in the flow loop. A programmable piston pump was used to generate the LV model wall motion. 2D Particle image velocimetry measurements were conducted along multiple longitudinal planes perpendicular to the annulus plane. During peak diastole, the incoming jet width at the LV central plane was smaller for the D-orifice than that of the O-orifice. Further, the core of the vortex ring in the D-orifice was reduced in size compared to that of the O-orifice. The spatiotemporal spreading of the inflow jet as well as the propagation of the vortex ring will be discussed. This study was funded by a grant from the National Heart, Lung and Blood Institute (RO1HL70262).

  11. Modeling Pulse Tube Cryocoolers with CFD

    NASA Astrophysics Data System (ADS)

    Flake, Barrett; Razani, Arsalan

    2004-06-01

    A commercial computational fluid dynamics (CFD) software package is used to model the oscillating flow inside a pulse tube cryocooler. Capabilities for modeling pulse tubes are demonstrated with preliminary case studies and the results presented. The 2D axi-symmetric simulations demonstrate the time varying temperature and velocity fields in the tube along with computation of the heat fluxes at the hot and cold heat exchangers. The only externally imposed boundary conditions are a cyclically moving piston wall at one end of the tube and constant temperature or heat flux boundaries at the external walls of the hot and cold heat exchangers.

  12. Generic Sensor Modeling Using Pulse Method

    NASA Technical Reports Server (NTRS)

    Helder, Dennis L.; Choi, Taeyoung

    2005-01-01

    Recent development of high spatial resolution satellites such as IKONOS, Quickbird and Orbview enable observation of the Earth's surface with sub-meter resolution. Compared to the 30 meter resolution of Landsat 5 TM, the amount of information in the output image was dramatically increased. In this era of high spatial resolution, the estimation of spatial quality of images is gaining attention. Historically, the Modulation Transfer Function (MTF) concept has been used to estimate an imaging system's spatial quality. Sometimes classified by target shapes, various methods were developed in laboratory environment utilizing sinusoidal inputs, periodic bar patterns and narrow slits. On-orbit sensor MTF estimation was performed on 30-meter GSD Landsat4 Thematic Mapper (TM) data from the bridge pulse target as a pulse input . Because of a high resolution sensor s small Ground Sampling Distance (GSD), reasonably sized man-made edge, pulse, and impulse targets can be deployed on a uniform grassy area with accurate control of ground targets using tarps and convex mirrors. All the previous work cited calculated MTF without testing the MTF estimator's performance. In previous report, a numerical generic sensor model had been developed to simulate and improve the performance of on-orbit MTF estimating techniques. Results from the previous sensor modeling report that have been incorporated into standard MTF estimation work include Fermi edge detection and the newly developed 4th order modified Savitzky-Golay (MSG) interpolation technique. Noise sensitivity had been studied by performing simulations on known noise sources and a sensor model. Extensive investigation was done to characterize multi-resolution ground noise. Finally, angle simulation was tested by using synthetic pulse targets with angles from 2 to 15 degrees, several brightness levels, and different noise levels from both ground targets and imaging system. As a continuing research activity using the developed sensor

  13. [Natural orifice transluminal endoscopic surgery: current situation].

    PubMed

    Delgado, Salvadora; Ibarzábal, Ainitze; Fernández-Esparrach, Glòria

    2008-10-01

    Natural orifice transluminal endoscopic surgery (NOTES) is the paradigm of the evolution of minimally invasive surgery. The laparoscopic has introduced new ideas in general surgery, one of them being that modern surgery is the work of multidisciplinary teams. A clear example of this is provided by NOTES. The aim of this type of surgery is to perform conventional laparoscopic procedures without incision, using flexible endoscopic technology usually employed in the diagnosis and treatment of intraluminal lesions and reaching the inside of the abdominal cavity through natural orifices (mouth, anus, vagina and even urethra). This type of access opens a highly interesting field for certain types of patients, such as those with high surgical risk, the morbidly obese, and those with multiple prior abdominal interventions or surgical wound infections. Animal models have shown that a wide variety of interventions (cholecystectomy, appendicectomy, splenectomy, hysterectomy, tubal ligations, gastroenteroanastomosis, peritoneoscopy, liver biopsy and herniorrhaphy, among others) can be performed. However, before use in humans, this new technique must be shown to be safe and to provide real advantages for patients. To do this, a series of issues, including safe methods for closure of the gastric incision and the avoidance of infections, among others, must be solved. Another critical element for the development of this new type of surgery is the creation of appropriate instrumentation, requiring input not only from medical professionals but also from engineers and industry. The present article describes the major advances made in NOTES since this technique was first described and analyzes the risks and potential benefits associated with this novel procedure. PMID:18928752

  14. Modelling the pulse transformer in SPICE

    NASA Astrophysics Data System (ADS)

    Godlewska, Malgorzata; Górecki, Krzysztof; Górski, Krzysztof

    2016-01-01

    The paper is devoted to modelling pulse transformers in SPICE. It shows the character of the selected models of this element, points out their advantages and disadvantages, and presents the results of experimental verification of the considered models. These models are characterized by varying degrees of complexity - from linearly coupled linear coils to nonlinear electrothermal models. The study was conducted for transformer with ring cores made of a variety of ferromagnetic materials, while exciting the sinusoidal signal of a frequency 100 kHz and different values of load resistance. The transformers operating conditions under which the considered models ensure the acceptable accuracy of calculations are indicated.

  15. Gas Generator Feedline Orifice Sizing Methodology: Effects of Unsteadiness and Non-Axisymmetric Flow

    NASA Technical Reports Server (NTRS)

    Rothermel, Jeffry; West, Jeffrey S.

    2011-01-01

    Engine LH2 and LO2 gas generator feed assemblies were modeled with computational fluid dynamics (CFD) methods at 100% rated power level, using on-center square- and round-edge orifices. The purpose of the orifices is to regulate the flow of fuel and oxidizer to the gas generator, enabling optimal power supply to the turbine and pump assemblies. The unsteady Reynolds-Averaged Navier-Stokes equations were solved on unstructured grids at second-order spatial and temporal accuracy. The LO2 model was validated against published experimental data and semi-empirical relationships for thin-plate orifices over a range of Reynolds numbers. Predictions for the LO2 square- and round-edge orifices precisely match experiment and semi-empirical formulas, despite complex feedline geometry whereby a portion of the flow from the engine main feedlines travels at a right-angle through a smaller-diameter pipe containing the orifice. Predictions for LH2 square- and round-edge orifice designs match experiment and semi-empirical formulas to varying degrees depending on the semi-empirical formula being evaluated. LO2 mass flow rate through the square-edge orifice is predicted to be 25 percent less than the flow rate budgeted in the original engine balance, which was subsequently modified. LH2 mass flow rate through the square-edge orifice is predicted to be 5 percent greater than the flow rate budgeted in the engine balance. Since CFD predictions for LO2 and LH2 square-edge orifice pressure loss coefficients, K, both agree with published data, the equation for K has been used to define a procedure for orifice sizing.

  16. Preparation of spherical particles by vibrating orifice technique

    NASA Astrophysics Data System (ADS)

    Shibata, Shuichi; Tomizawa, Atsushi; Yoshikawa, Hidemi; Yano, Tetsuji; Yamane, Masayuki

    2000-05-01

    Preparation of micrometer-sized spherical particles containing Rhodamine 6G (R6G) has been investigated for the spherical cavity micro-laser. Using phenyl triethoxy silane (PTES) as a starting material, R6G-doped monodisperse spherical particles were prepared by the vibrating orifice technique. Processing consists of two major processes: (1) Hydrolysis and polymerization of PTES and (2) Droplet formation from PTES oligomers by vibrating orifice technique. A cylindrical liquid jet passing through the orifice of 10 and 20 micrometers in diameter breaks up into equal- sized droplets by mechanical vibration. Alcohol solvent of these droplets was evaporated during flying with carrier gas and subsequently solidified in ammonium water trap. For making smooth surface and god shaped particles, control of molecular weight of PTES oligomer was essential. R6G-doped hybrid spherical particles of 4 to 10 micrometers size of cavity structure were successfully obtained. The spherical particles were pumped by a second harmonic pulse of Q- switched Nd:YAG laser and laser emission peaks were observed at wavelengths which correspond to the resonance modes.

  17. Orifice Blocks Heat Pipe in Reverse Mode

    NASA Technical Reports Server (NTRS)

    Alario, J. P.

    1982-01-01

    High forward-mode conductance is combined with rapid reverse-mode shutoff in a heat pipe originally developed to cool spacecraft payloads. A narrow orifice within the pipe "chokes off" the evaporator if heat sink becomes warmer than source. During normal operation, with source warmer than sink, orifice has little effect. Design is simpler and more compact than other thermal-diode heat pipes and requires no special materials, forgings, or unusual construction techniques.

  18. Improved Orifice Plate for Spray Gun

    NASA Technical Reports Server (NTRS)

    Cunningham, W.

    1986-01-01

    Erratic spray pattern of commercial spray gun changed to repeatable one by simple redesign of two parts. In modified spray gun orifice plate and polytetrafluoroethylene bushing redesigned to assure centering and alignment with nozzle. Such improvement useful in many industrial applications requiring repeatable spray patterns. Might include spraying of foam insulation, paint, other protective coatings, detergents, abrasives, adhesives, process chemicals, or fuels. Unmodified spray gun produces erratic spray because lateral misalignment between orifice plate and nozzle.

  19. Transanal natural orifice transluminal endoscopic surgery total mesorectal excision in animal models: endoscopic inferior mesenteric artery dissection made easier by a retroperitoneal approach

    PubMed Central

    Park, Sun Jin; Chang, Tae Young; Jung, Yunho; Kim, Hyung Jin; Kim, Young Ill; Chun, Ho-Kyung

    2014-01-01

    Purpose We report the performance of natural orifice transluminal endoscopic surgery (NOTES) low anterior resection in animals using transanal total mesorectal excision (TME) with laparoscopic assistance and endoscopic inferior mesenteric artery (IMA) dissection. Methods Four pigs weighing 45 kg each, and one dog weighing 25 kg, underwent surgery via a transanal approach. The rectum was occluded transanally using a purse-string suture, approximately 3-4 cm from the anal verge. The rectal mucosa was incised circumferentially just distal to the purse-string. A SILS or GelPOINT port was inserted transanally. Transanal TME was assisted by laparoscopy and proceeded up to the peritoneal reflection. More proximal dissection, including IMA dissection, was performed along the retroperitoneal avascular plane by endoscopy alone and facilitated by CO2 insufflation. The IMA was clipped and divided endoscopically. The mobilized rectosigmoid were exteriorized transanally and transected. A colorectal anastomosis was performed using a circular stapler with a single stapling technique. Results Endoscopic dissection of the IMA was successful in all five animals. The mean operation time was 125 minutes (range, 90-170 minutes). There were no intraoperative complications or hemodynamic instability. The mean length of the resected specimen was 14.4 cm (range, 12-16 cm). Conclusion A NOTES retroperitoneal approach to the IMA with CO2 insufflation and intact peritoneal covering overcame the difficulties of retraction and exposure of endoscopic dissection in animals. PMID:25025019

  20. Slotted orifice flowmeter. Final report, July 1993-August 1995

    SciTech Connect

    Morrison, G.L.

    1995-09-01

    The report shows that a slotted orifice has superior performance characteristics compared to a standard orifice by being significantly less dependent upon upstream flow conditioning than a standard orifice plate. The effectiveness of the slotted orifice as a flow condition is shown.

  1. TWO-PHASE FLOW OF TWO HFC REFRIGERANT MIXTURES THROUGH SHORT-TUBE ORIFICES

    EPA Science Inventory

    The report gives results of an experimental investigation to develop an acceptable flow model for short tube orifice expansion devices used in heat pumps. The refrigerants investigated were two hydrofluorocarbon (HFC) mixtures considered hydrochlorofluorocarbon (HCFC)-22 replacem...

  2. Modeling of pulsed lasers for remote sensing

    NASA Astrophysics Data System (ADS)

    Walsh, Brian M.; Barnes, Norman P.; Petros, Mulugeta; Yu, Jirong; Singh, Upendra N.

    2005-01-01

    Pulsed lasers are useful for remote sensing of wind and greenhouse gases to better understand the atmosphere and its impact on weather patterns and the environment. It is not always practical to develop and optimize new laser systems empirically due to the time and expense associated with such endeavors. A practical option is to use a laser model to predict various performance parameters and compare these with the needs required for a particular remote sensing application. This approach can be very useful in determining the efficacy of potential laser systems, saving both time and money before proceeding with the actual construction of a laser device. As a pedagogical example, the modeling of diode pumped Tm:Ho:YLF and Tm:Ho:LuLF lasers are examined. Tm:Ho lasers operating around 2.0 μm have been used for wind measurements such as clear air turbulence and wake vortices. The model predictions for the laser systems examined here are compared to the actual laser performance, validating the usefulness of the modeling approach. While Tm:Ho fluoride lasers are used as a pedagogical example, the model is applicable to any lanthanide series pulsed laser system. This provides a useful tool for investigating potential laser systems that meet the requirements desired for a variety of remote sensing applications.

  3. Comparison of turbulent flow through hexagram and hexagon orifices in circular pipes using large-eddy simulation

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Nicolleau, Franck C. G. A.; Qin, Ning

    2016-04-01

    Characteristics of turbulent flow through a circular, a hexagon and a hexagram orifice with the same flow area in circular pipes are investigated using wall-modelled large-eddy simulation. Good agreements to available experimental data were obtained in both the mean velocity and turbulent kinetic energy. The hexagram orifice with alternating convex and concave corners introduces outwards radial velocity around the concave corners downstream of the orifice plate stronger than the hexagon orifice. The stronger outwards radial velocity transfers high momentum from the pipe centre towards the pipe wall to energize the orifice-forced vortex sheet rolling-up and leads to a delayed vortex break-down. Correspondingly, the hexagram has a more gradual flow recovery to a pipe flow and a reduced pressure drop than the hexagon orifice. Both the hexagon and hexagram orifices show an axis-switching phenomenon, which is observed from both the streamwise velocity and turbulent kinetic energy contours. To the best knowledge of the authors, this is the first comparison of orifice-forced turbulence development, mixing and flow dynamics between a regular and a fractal-based polygonal orifice.

  4. Anesthetic management of transoral natural orifice transluminal endoscopic surgery: two cases report

    PubMed Central

    Chung, Chan Jong; Lee, Seung Cheo; Shin, Ho Jin

    2014-01-01

    Natural orifice transluminal endoscopic surgery (NOTES) is an evolving field of minimally invasive surgery. NOTES reaches the target organ by inserting the endoscope through a natural orifice (e.g. mouth, anus, urethra, vagina) and offers advantages of less postoperative pain and lower complication rate. Since its first description in 2004, NOTES has progressed from use on animal models to humans. We experienced anesthetic care of two patients who underwent transoral NOTES under general anesthesia. PMID:25237454

  5. Bubble Formation at a Submerged Orifice in Reduced Gravity

    NASA Technical Reports Server (NTRS)

    Buyevich, Yu A.; Webbon, Bruce W.

    1994-01-01

    The dynamic regime of gas injection through a circular plate orifice into an ideally wetting liquid is considered, when successively detached bubbles may be regarded as separate identities. In normal gravity and at relatively low gas flow rates, a growing bubble is modeled as a spherical segment touching the orifice perimeter during the whole time of its evolution. If the flow rate exceeds a certain threshold value, another stage of the detachment process takes place in which an almost spherical gas envelope is connected with the orifice by a nearly cylindrical stem that lengthens as the bubble rises above the plate. The bubble shape resembles then that of a mushroom and the upper envelope continues to grow until the gas supply through the stem is completely cut off. Such a stage is always present under conditions of sufficiently low gravity, irrespective of the flow rate. Two major reasons make for bubble detachment: the buoyancy force and the force due to the momentum inflow into the bubble with the injected gas. The former force dominates the process at normal gravity whereas the second one plays a key role under negligible gravity conditions. It is precisely this fundamental factor that conditions the drastic influence on bubble growth and detachment that changes in gravity are able to cause. The frequency of bubble formation is proportional to and the volume of detached bubbles is independent of the gas flow rate in sufficiently low gravity, while at normal and moderately reduced gravity conditions the first variable slightly decreases and the second one almost linearly increases as the flow rate grows. Effects of other parameters, such as the orifice radius, gas and liquid densities, and surface tension are discussed.

  6. Modeling and analysis of pulse electrochemical machining

    NASA Astrophysics Data System (ADS)

    Wei, Bin

    Pulse Electrochemical Machining (PECM) is a potentially cost effective technology meeting the increasing needs of precision manufacturing of superalloys, like titanium alloys, into complex shapes such as turbine airfoils. This dissertation reports: (1) an assessment of the worldwide state-of-the-art PECM research and industrial practice; (2) PECM process model development; (3) PECM of a superalloy (Ti-6Al-4V); and (4) key issues in future PECM research. The assessment focuses on identifying dimensional control problems with continuous ECM and how PECM can offer a solution. Previous research on PECM system design, process mechanisms, and dimensional control is analysed, leading to a clearer understanding of key issues in PECM development such as process characterization and modeling. New interelectrode gap dynamic models describing the gap evolution with time are developed for different PECM processes with an emphasis on the frontal gaps and a typical two-dimensional case. A 'PECM cosine principle' and several tool design formulae are also derived. PECM processes are characterized using concepts such as quasi-equilibrium gap and dissolution localization. Process simulation is performed to evaluate the effects of process inputs on dimensional accuracy control. Analysis is made on three types (single-phase, homogeneous, and inhomogeneous) of models concerning the physical processes (such as the electrolyte flow, Joule heating, and bubble generation) in the interelectrode gap. A physical model is introduced for the PECM with short pulses, which addresses the effect of electrolyte conductivity change on anodic dissolution. PECM of the titanium alloy is studied from a new perspective on the pulsating currents influence on surface quality and dimension control. An experimental methodology is developed to acquire instantaneous currents and to accurately measure the coefficient of machinability. The influence of pulse parameters on the surface passivation is explained based

  7. Effects of Ultrasmall Orifices on the Electro-generation of Femtoliter-Volume Aqueous Droplets

    PubMed Central

    He, Mingyan; Kuo, Jason S.; Chiu, Daniel T.

    2008-01-01

    The ability to generate individual picoliter- and femtoliter-volume aqueous droplets on-demand is useful for encapsulating and chemically manipulating discrete chemical and biological samples. This paper characterizes the effects of orifice dimensions and material choices on generating such droplets in an immiscible oil phase using single high-voltage pulses with various amplitudes and durations. We have examined microfluidic orifices as small as 1.7 μm in equivalent radii, and found that the electrohydrodynamic jet lengths and the subsequent formation of droplets are affected by the axial aspect ratios of the orifices (length of an orifice divided by its equivalent radius). As higher voltages were used to compensate for the increased capillary pressure and hydrodynamic resistance in ultrasmall orifices, we observed secondary jet protrusions and droplet formations that were not of classical electrohydrodynamic origin. The droplets generated from secondary jets traveled at relatively lower velocities as compared to those of electrohydrodynamic origin, and these slow individual droplets are potentially more useful for applications in microscale chemical reactions. PMID:16800707

  8. Contoured Orifice for Silicon-Ribbon Die

    NASA Technical Reports Server (NTRS)

    Mackintosh, B. H.

    1985-01-01

    Die configuration encourages purity and stable growth. Contour of die orifice changes near ribbon edges. As result, silicon ribbon has nearly constant width and little carbon contamination. Die part of furnace being developed to produce high-quality, low-cost material for solar cells.

  9. Variable orifice using an iris shutter

    DOEpatents

    Beeman, Raymond; Brajkovich, Steven J.

    1978-01-01

    A variable orifice forming mechanism utilizing an iris shutter arrangement adapted to control gas flow, conductance in vacuum systems, as a heat shield for furnace windows, as a beam shutter in sputtering operations, and in any other application requiring periodic or continuously-variable control of material, gas, or fluid flow.

  10. Investigation of drop motion through circular orifices

    NASA Astrophysics Data System (ADS)

    Bordoloi, Ankur; Longmire, Ellen; Kong, Xiangzhao; Saar, Martin

    2011-11-01

    The motion of drops though porous media occurs in numerous science and engineering fields including multiphase fluid flow in the subsurface during groundwater flow, geothermal energy recovery, and geologic carbon dioxide sequestration. Here, we simplify the porous medium to a thin plate with an orifice to study the interactions between the drop and the solid medium. Drops of water/glycerin with diameter, D, are released in a tank of silicone oil with matched refractive index and allowed to fall downward by gravity. After reaching terminal speed, the drops encounter a thin plate with orifice diameter, d, placed horizontally within the surrounding tank. Drop deformation, contact with the orifice, and breakage are investigated using high-speed imaging, and velocity fields are determined by particle image velocimetry (PIV). Effects of diameter ratio d/D, drop Reynolds number, and drop offset with respect to the orifice center are examined. The experimental results are compared to results from numerical simulations using an immiscible, two-color BGK lattice-Boltzmann method performed under similar test conditions. Supported by DOE (DOE EERE-PMC-10EE0002764).

  11. Update on Natural Orifice Translumenal Endoscopic Surgery

    PubMed Central

    Bingener, Juliane; Gostout, Christopher J.

    2012-01-01

    Natural orifice translumenal endoscopic surgery (NOTES) has moved from the realm of laboratory experiments to the realm of human clinical trials. This paper reviews the spectrum of NOTES procedures currently available in the United States and worldwide. It also discusses the limitations and avenues for further development of these procedures, particularly those involving the transgastric approach. PMID:22933874

  12. Measurements and computational fluid dynamics predictions of the acoustic impedance of orifices

    NASA Astrophysics Data System (ADS)

    Su, J.; Rupp, J.; Garmory, A.; Carrotte, J. F.

    2015-09-01

    The response of orifices to incident acoustic waves, which is important for many engineering applications, is investigated with an approach combining both experimental measurements and numerical simulations. This paper presents experimental data on acoustic impedance of orifices, which is subsequently used for validation of a numerical technique developed for the purpose of predicting the acoustic response of a range of geometries with moderate computational cost. Measurements are conducted for orifices with length to diameter ratios, L/D, of 0.5, 5 and 10. The experimental data is obtained for a range of frequencies using a configuration in which a mean (or bias) flow passes from a duct through the test orifices before issuing into a plenum. Acoustic waves are provided by a sound generator on the upstream side of the orifices. Computational fluid dynamics (CFD) calculations of the same configuration have also been performed. These have been undertaken using an unsteady Reynolds averaged Navier-Stokes (URANS) approach with a pressure based compressible formulation with appropriate characteristic based boundary conditions to simulate the correct acoustic behaviour at the boundaries. The CFD predictions are in very good agreement with the experimental data, predicting the correct trend with both frequency and orifice L/D in a way not seen with analytical models. The CFD was also able to successfully predict a negative resistance, and hence a reflection coefficient greater than unity for the L / D = 0.5 case.

  13. Pressure drop control using multiple orifice system in compressible pipe flows

    NASA Astrophysics Data System (ADS)

    Kim, Heuydong; Setoguchi, Toshiaki; Matsuo, Shigeru; Raghunathan, S. R.

    2001-10-01

    In order to investigate the effectiveness of an orifice system in producing pressure drops and the effect of compressibility on the pressure drop, computations using the mass-averaged implicit Navier-Stokes equations were applied to the axisymmetric pipe flows with the operating pressure ratio from 1.5 to 20.0. The standard k- ɛ turbulence model was employed to close the governing equations. Numerical calculations were carried out for some combinations of the multiple orifice configurations. The present CFD data showed that the orifice systems, which have been applied to incompressible flow regime to date, could not be used for the high operating pressure ratio flows. The orifice interval did not strongly affect the total pressure drop, but the orifice area ratio more than 2.5 led to relatively high pressure drops. The total pressure drop rapidly increased in the range of the operating pressure ratio from 1.5 to 4.0, but it nearly did not increase when the operating pressure ratio was over 4.0. In the compressible pipe flows through double and triple orifice systems, the total pressure drop was largely due to shock losses.

  14. Future Modeling Needs in Pulse Detonation Rocket Engine Design

    NASA Technical Reports Server (NTRS)

    Meade, Brian; Talley, Doug; Mueller, Donn; Tew, Dave; Guidos, Mike; Seymour, Dave

    2001-01-01

    This paper presents a performance model rocket engine design that takes advantage of pulse detonation to generate thrust. The contents include: 1) Introduction to the Pulse Detonation Rocket Engine (PDRE); 2) PDRE modeling issues and options; 3) Discussion of the PDRE Performance Workshop held at Marshall Space Flight Center; and 4) Identify needs involving an open performance model for Pulse Detonation Rocket Engines. This paper is in viewgraph form.

  15. Modelling of noise-like pulses generated in fibre lasers

    NASA Astrophysics Data System (ADS)

    Smirnov, Sergey; Kobtsev, Sergey

    2016-03-01

    The present paper for the first time proposes and studies a relatively simple model of noise-like pulses that matches the experimental data well and suggests that there is a correlation between phases of adjacent spectral components of noiselike pulses. Comparison of a relatively basic model of `random' pulses with the results of noise-like pulse modelling in mode-locked fibre lasers based on coupled non-linear Schrödinger equations demonstrates that it adequately reproduces temporal and spectral properties of noise-like pulses as well as correlation between adjacent modes so that it's possible to use the proposed model for highly efficient simulations of promising applications of noise-like pulses, such as material processing, non-linear frequency conversion, microscopy, and others.

  16. The underground electromagnetic pulse: Four representative models

    SciTech Connect

    Wouters, L.F.

    1989-06-01

    I describe four phenomenological models by which an underground nuclear explosion may generate electromagnetic pulses: Compton current asymmetry (or ''Compton dipole''); Uphole conductor currents (or ''casing currents''); Diamagnetic cavity plasma (or ''magnetic bubble''); and Large-scale ground motion (or ''magneto-acoustic wave''). I outline the corresponding analytic exercises and summarize the principal results of the computations. I used a 10-kt contained explosion as the fiducial case. Each analytic sequence developed an equivalent source dipole and calculated signal waveforms at representative ground-surface locations. As a comparative summary, the Compton dipole generates a peak source current moment of about 12,000 A/center dot/m in the submicrosecond time domain. The casing-current source model obtains an equivalent peak moment of about 2 /times/ 10/sup 5/ A/center dot/m in the 10- to 30-/mu/s domain. The magnetic bubble produces a magnetic dipole moment of about 7 /times/ 10/sup 6/ A/center dot/m/sup 2/, characterized by a 30-ms time structure. Finally, the magneto-acoustic wave corresponds to a magnetic dipole moment of about 600 A/center dot/m/sup 2/, with a waveform showing 0.5-s periodicities. 8 refs., 35 figs., 7 tabs.

  17. Natural orifice translumenal endoscopic radical prostatectomy

    PubMed Central

    Castle, Erik P.; Andrews, Paul E.; Lingeman, James E.

    2012-01-01

    The purpose of this publication is to document the evolution of a new surgical procedure for the treatment of carefully selected patients with organ confined localized prostate cancer. Natural orifice surgery represents a paradigm shift in the surgical approach to disease, although its adoption into clinical practice has been limited to date. This manuscript describes the development of natural orifice translumenal endoscopic surgical radical prostatectomy (NOTES RP). The laboratory, animal, preclinical and early clinical experiences are described and detailed. While the early experiences with this approach are promising and encouraging, more information is required. Despite the early successes with the procedure, long-term oncological and functional outcomes are essential and more work needs to be done to facilitate the teaching and ease of the NOTES RP. PMID:22295043

  18. Hydraulic design and performance of a GCFR core assembly orifice

    SciTech Connect

    Tang, I.M.

    1980-02-01

    The design and performance of a core assembly orifice for gas-cooled fast-breeder reactors (GCFRs) are studied in this report. Successful reactor operation relies on adequate cooling, among other things, and orificing is important to cooling. A simple, yet effective, graphical design method for estimating the loss coefficient of an orifice and its associated opening area is presented. A numerical example is also provided for demonstration of the method. The effect of the orifice configuration on orifice hydraulic performance is discussed. The design method stated above provides a first estimate toward an orifice design. Hydraulic experiments are required for verification of the design adequacy.

  19. [Natural orifice translumenal endoscopic surgery: historical and future perspectives].

    PubMed

    Yasuda, Kazuhiro; Shiroshita, Hidefumi; Inomata, Masafumi; Kitano, Seigo

    2013-11-01

    Natural orifice translumenal endoscopic surgery (NOTES) has gained much attention worldwide since the first report of transgastric peritoneoscopy in a porcine model in 2004. In this review, we summarize and highlight the current status and future directions of NOTES. Thousands of human NOTES procedures have been performed. The most common procedures are cholecystectomy and appendectomy, mainly performed through transvaginal access in a hybrid fashion with laparoscopic assistance, and the general complication rate is acceptable. Although much work is still needed to refine the techniques for NOTES, the development of NOTES has the potential to create a paradigm shift in minimally invasive surgery. PMID:24358724

  20. Acoustic Absorption Characteristics of an Orifice With a Mean Bias Flow

    NASA Technical Reports Server (NTRS)

    Ahuja, K. K.; Gaeta, R. J., Jr.; DAgostino, M.; Jones, Mike (Technical Monitor)

    2000-01-01

    The objective of the study reported here was to acquire acoustic and flow data for numerical validation of impedance models that simulate bias flow through perforates. The impedance model is being developed by researchers at High Technology Corporation. This report documents normal incidence impedance measurements a singular circular orifice with mean flow passing through it. All measurements are made within a 1.12 inch (28.5 mm) diameter impedance tube. The mean flow is introduced upstream of the orifice (with the flow and incident sound wave travelling in the same direction) with an anechoic termination downstream of the orifice. Velocity profiles are obtained upstream of the orifice to characterize the inflow boundary conditions. Velocity in the center of the orifice is also obtained. All velocity measurements are made with a hot wire anemometer and subsequent checked with mass flow measurements made concurrently. All impedance measurements are made using the Two-Microphone Method. Although we have left the analysis of the data to the developers of the impedance models that simulate bias flow through perforate, our initial examination indicates that our results follow the trends consistent with published theory on impedance of perforates with a steady bias flow.

  1. Modeling propagation of coherent optical pulses through molecular vapor

    SciTech Connect

    Shore, B.W.; Eberly, J.H.

    1982-01-01

    Results of modeling the mutual coupling of coherent molecular response and coherent optical pulses during propagation are described. The propagation is treated numerically, with particular emphasis on both continuum and discrete behavior associated with the quasicontinuum model.

  2. Effect of grazing flow on the acoustic impedance of Helmholtz resonators consisting of single and clustered orifices

    NASA Technical Reports Server (NTRS)

    Hersch, A. S.; Walker, B.

    1979-01-01

    A semiempirical fluid mechanical model is derived for the acoustic behavior of thin-walled single orifice Helmholtz resonators in a grazing flow environment. The incident and cavity sound fields are connected in terms of an orifice discharge coefficient whose values are determined experimentally using the two-microphone method. Measurements show that at high grazing flow speeds, acoustical resistance is almost linearly proportional to the grazing flow speed and almost independent of incident sound pressure. The corresponding values of reactance are much smaller and tend towards zero. For thicker-walled orifice plates, resistance and reactance were observed to be less sensitive to grazing flow as the ratio of plate thickness to orifice diameter increased. Loud tones were observed to radiate from a single orifice Helmholtz resonator due to interaction between the grazing flow shear layer and the resonator cavity. Measurements showed that the tones radiated at a Strouhal number equal to 0.26. The effects of grazing flow on the impedance of Helmholtz resonators consisting of clusters of orifices was also studied. In general, both resistance and reaction were found to be virtually independent of orifice relative spacing and number. These findings are valid with and without grazing flow.

  3. Dynamic model of target charging by short laser pulse interactions.

    PubMed

    Poyé, A; Dubois, J-L; Lubrano-Lavaderci, F; D'Humières, E; Bardon, M; Hulin, S; Bailly-Grandvaux, M; Ribolzi, J; Raffestin, D; Santos, J J; Nicolaï, Ph; Tikhonchuk, V

    2015-10-01

    A model providing an accurate estimate of the charge accumulation on the surface of a metallic target irradiated by a high-intensity laser pulse of fs-ps duration is proposed. The model is confirmed by detailed comparisons with specially designed experiments. Such a model is useful for understanding the electromagnetic pulse emission and the quasistatic magnetic field generation in laser-plasma interaction experiments. PMID:26565356

  4. Dynamic model of target charging by short laser pulse interactions

    NASA Astrophysics Data System (ADS)

    Poyé, A.; Dubois, J.-L.; Lubrano-Lavaderci, F.; D'Humières, E.; Bardon, M.; Hulin, S.; Bailly-Grandvaux, M.; Ribolzi, J.; Raffestin, D.; Santos, J. J.; Nicolaï, Ph.; Tikhonchuk, V.

    2015-10-01

    A model providing an accurate estimate of the charge accumulation on the surface of a metallic target irradiated by a high-intensity laser pulse of fs-ps duration is proposed. The model is confirmed by detailed comparisons with specially designed experiments. Such a model is useful for understanding the electromagnetic pulse emission and the quasistatic magnetic field generation in laser-plasma interaction experiments.

  5. Pulse

    MedlinePlus

    Heart rate; Heart beat ... The pulse can be measured at areas where an artery passes close to the skin. These areas include the: ... side of the foot Wrist To measure the pulse at the wrist, place the index and middle ...

  6. Natural orifice translumenal surgery: Flexible platform review

    PubMed Central

    Shaikh, Sohail N; Thompson, Christopher C

    2010-01-01

    Natural orifice translumenal surgery (NOTES) has garnished significant attention from surgeons and gastroenterologists, due to the fusion of flexible endoscopy and operative technique. Preliminary efforts suggest that NOTES holds potential for a less invasive approach with certain surgical conditions. Many of the hurdles encountered during the shift from open to laparoscopic surgery are now being revisited in the development of NOTES. Physician directed efforts, coupled with industry support, have brought about several NOTES specific devices and platforms to help address limitations with current instrumentation. This review addresses current flexible platforms and their attributes, advantages, disadvantages and limitations. PMID:21160877

  7. Natural orifice transluminal endoscopy surgery: A review

    PubMed Central

    Moreira-Pinto, João; Lima, Estevão; Correia-Pinto, Jorge; Rolanda, Carla

    2011-01-01

    Minimally invasive surgery started spreading worldwide in 1987, when the first laparoscopic cholecystectomy was performed. Meanwhile, improvement of endoscopic equipment and instruments allowed gastroenterologists to attempt more aggressive endoluminal interventions, even beyond the wall barrier. The first transgastric peritoneoscopy, in 2004, brought to light the concept of natural orifice transluminal endoscopic surgery (NOTES). The idea of incisionless surgery is attractive and has become a new goal for both surgeons and other people interested in this field of investigation. The authors present a review of all developments concerning NOTES, including animal studies and human experience. PMID:21987621

  8. Study of orifice fabrication technologies for the liquid droplet radiator

    NASA Technical Reports Server (NTRS)

    Wallace, David B.; Hayes, Donald J.; Bush, J. Michael

    1991-01-01

    Eleven orifice fabrication technologies potentially applicable for a liquid droplet radiator are discussed. The evaluation is focused on technologies capable of yielding 25-150 microns diameter orifices with trajectory accuracies below 5 milliradians, ultimately in arrays of up to 4000 orifices. An initial analytical screening considering factors such as trajectory accuracy, manufacturability, and hydrodynamics of orifice flow is presented. Based on this screening, four technologies were selected for experimental evaluation. A jet straightness system used to test 50-orifice arrays made by electro-discharge machining (EDM), Fotoceram, and mechanical drilling is discussed. Measurements on orifice diameter control and jet trajectory accuracy are presented and discussed. Trajectory standard deviations are in the 4.6-10.0 milliradian range. Electroforming and EDM appear to have the greatest potential for Liquid Droplet Radiator applications. The direction of a future development effort is discussed.

  9. Pulsed Ejector Thrust Amplification Tested and Modeled

    NASA Technical Reports Server (NTRS)

    Wilson, Jack

    2004-01-01

    There is currently much interest in pulsed detonation engines for aeronautical propulsion. This, in turn, has sparked renewed interest in pulsed ejectors to increase the thrust of such engines, since previous, though limited, research had indicated that pulsed ejectors could double the thrust in a short device. An experiment has been run at the NASA Glenn Research Center, using a shrouded Hartmann-Sprenger tube as a source of pulsed flow, to measure the thrust augmentation of a statistically designed set of ejectors. A Hartmann- Sprenger tube directs the flow from a supersonic nozzle (Mach 2 in the present experiment) into a closed tube. Under appropriate conditions, an oscillation is set up in which the jet flow alternately fills the tube and then spills around flow emerging from the tube. The tube length determines the frequency of oscillation. By shrouding the tube, the flow was directed out of the shroud as an axial stream. The set of ejectors comprised three different ejector lengths, three ejector diameters, and three nose radii. The thrust of the jet alone, and then of the jet plus ejector, was measured using a thrust plate. The arrangement is shown in this photograph. Thrust augmentation is defined as the thrust of the jet with an ejector divided by the thrust of the jet alone. The experiments exhibited an optimum ejector diameter and length for maximizing the thrust augmentation, but little dependence on nose radius. Different frequencies were produced by changing the length of the Hartmann-Sprenger tube, and the experiment was run at a total of four frequencies. Additional measurements showed that the major feature of the pulsed jet was a starting vortex ring. The size of the vortex ring depended on the frequency, as did the optimum ejector diameter.

  10. Bubble Formation at a Submerged Orifice for Aluminum Foams Produced by Gas Injection Method

    NASA Astrophysics Data System (ADS)

    Fan, Xueliu; Chen, Xiang; Liu, Xingnan; Zhang, Huiming; Li, Yanxiang

    2013-02-01

    The bubble formation at a submerged orifice in the process of aluminum foams produced by gas injection method is investigated. The experimental results show that the increase of the gas flow rate and the orifice diameter can lead to increasing of the bubble size. The large orifice can make the frequency of bubble formation decrease by slowing down the increase of the gas chamber pressure when the gas flow rate increases. The effect of the gas chamber volume on the bubble size can be ignored in the experiment when it expands from 1 to 125 cm3. A theoretical model of bubble formation, expansion, and detachment under constant flow conditions is established to predict the bubble size. The theoretical predictions for air-aluminum melt systems are consistent with the experimental results.

  11. Quasi-One-Dimensional Modeling of Pulse Detonation Rocket Engines

    NASA Technical Reports Server (NTRS)

    Morris, Christopher I.

    2003-01-01

    This viewgraph presentation provides information on the engine cycle of a pulse detonation rocket engine (PDRE), models for optimizing the performance of a PDRE, and the performance of PDREs in comparison to Solid State Rocket Engines (SSREs).

  12. Finite element modeling of pulsed eddy current NDT phenomena

    SciTech Connect

    Allen, B.; Ida, N.; Lord, W.

    1985-05-15

    Transient fields for nondestructive testing (pulsed eddy current methods) have been used experimentally for such applications as coating thickness measurements and the inspection of reactor fuel tubing. The lack of suitable models to facilitate understanding of the interaction of the pulsed field with the test specimen has hindered a wider acceptance of the method as a tool in NDT. Two models, based on the finite element technique are described. The first model, used for repetitive pulse train sources makes use of the Fourier series of the source current to solve a steady state problem for each significant harmonic. The harmonic solutions are then summed to produce the total EMF in the pickup coil. The second model is used for single pulse application. The response is calculated using an iterative time stepping solution. In both cases axisymmetric geometries are studied using a magnetic vector potential formulation. Solutions are compared with experimental results. 3 refs., 3 figs.

  13. Gaseous Nitrogen Orifice Mass Flow Calculator

    NASA Technical Reports Server (NTRS)

    Ritrivi, Charles

    2013-01-01

    The Gaseous Nitrogen (GN2) Orifice Mass Flow Calculator was used to determine Space Shuttle Orbiter Water Spray Boiler (WSB) GN2 high-pressure tank source depletion rates for various leak scenarios, and the ability of the GN2 consumables to support cooling of Auxiliary Power Unit (APU) lubrication during entry. The data was used to support flight rationale concerning loss of an orbiter APU/hydraulic system and mission work-arounds. The GN2 mass flow-rate calculator standardizes a method for rapid assessment of GN2 mass flow through various orifice sizes for various discharge coefficients, delta pressures, and temperatures. The calculator utilizes a 0.9-lb (0.4 kg) GN2 source regulated to 40 psia (.276 kPa). These parameters correspond to the Space Shuttle WSB GN2 Source and Water Tank Bellows, but can be changed in the spreadsheet to accommodate any system parameters. The calculator can be used to analyze a leak source, leak rate, gas consumables depletion time, and puncture diameter that simulates the measured GN2 system pressure drop.

  14. Force-displacement model for analysis of pulsed-GMAW

    NASA Astrophysics Data System (ADS)

    Arif, Nabeel; Lee, Jae Hak; Yoo, Choong Don

    2009-02-01

    A force-displacement model (FDM) is introduced in this work to analyse pulsed gas metal arc welding (GMAW). The drop detaching criterion is established based on the displacement of the pendant drop instead of the previous force balance criterion. The displacement of the drop is calculated by integrating the acceleration of the drop, and the force exerted on the drop is predicted using the modified force balance model coupled with wire melting. When the peak current, base current and time of pulsed-GMAW are given, the peak time for the one-drop one-pulse condition is determined using the FDM. While the peak current has the most significant effect on drop detachment, the initial drop mass prior to the peak time also influences the drop transfer. The FDM is applied to the dc as well as pulsed-GMAW, and the calculated results show good agreement with the experimental data.

  15. Increasing pulse wave velocity in a realistic cardiovascular model does not increase pulse pressure with age

    PubMed Central

    Mohiuddin, Mohammad W.; Rihani, Ryan J.; Laine, Glen A.

    2012-01-01

    The mechanism of the well-documented increase in aortic pulse pressure (PP) with age is disputed. Investigators assuming a classical windkessel model believe that increases in PP arise from decreases in total arterial compliance (Ctot) and increases in total peripheral resistance (Rtot) with age. Investigators assuming a more sophisticated pulse transmission model believe PP rises because increases in pulse wave velocity (cph) make the reflected pressure wave arrive earlier, augmenting systolic pressure. It has recently been shown, however, that increases in cph do not have a commensurate effect on the timing of the reflected wave. We therefore used a validated, large-scale, human arterial system model that includes realistic pulse wave transmission to determine whether increases in cph cause increased PP with age. First, we made the realistic arterial system model age dependent by altering cardiac output (CO), Rtot, Ctot, and cph to mimic the reported changes in these parameters from age 30 to 70. Then, cph was theoretically maintained constant, while Ctot, Rtot, and CO were altered. The predicted increase in PP with age was similar to the observed increase in PP. In a complementary approach, Ctot, Rtot, and CO were theoretically maintained constant, and cph was increased. The predicted increase in PP was negligible. We found that increases in cph have a limited effect on the timing of the reflected wave but cause the system to degenerate into a windkessel. Changes in PP can therefore be attributed to a decrease in Ctot. PMID:22561301

  16. A simple expression for pressure drops of water and other low molecular liquids in the flow through micro-orifices

    NASA Astrophysics Data System (ADS)

    Hasegawa, Tomiichi; Ushida, Akiomi; Narumi, Takatsune

    2015-12-01

    Flows are generally divided into two types: shear flows and shear-free elongational (extensional) flows. Both are necessary for a thorough understanding of the flow properties of a fluid. Shear flows are easy to achieve in practice, for example, through Poiseuille or Couette flows. Shear-free elongational flows are experimentally hard to achieve, resulting in an incomplete understanding of the flow properties of fluids in micro-devices. Nevertheless, flows through micro-orifices are useful for probing the properties of elongational flows at high elongational rates; although these flows exhibit shear and elongation, the elongation is dominant and the shear is negligible in the central region of the flows. We previously reported an anomalous reduction in pressure drops in the flows of water, a 50/50 mixture of glycerol and water, and silicone oils through micro-orifices. In the present paper, we rearrange the data presented in the previous paper and reveal a simple relationship where the pressure drop is proportional to the velocity through the micro-orifices, independent of the orifice diameter and the viscosity of the liquids tested. We explain our observations by introducing a "fluid element" model, in which fluid elements are formed on entering the orifice. The model is based on the idea that low molecular liquids, including water, generate strong elongational stress, similar to a polymer solution, in the flow through micro-orifices.

  17. Double-orifice mitral valve associated with atrioventricular canal defects

    PubMed Central

    Rhissassi, Jaafar; El Malki, Hicham; Benmessaoud, Fatima Azzahra; El Kandoussi, Tahar; Laaroussi, Mohamed

    2016-01-01

    A 4 year-old male presented with effort dyspnea, and was diagnosed as atrioventricular canal defects. This finding was confirmed by open heart surgery, and a congenital double orifice mitral valve was discovered. The septal defect was closed but the double orifice mitral valve was respected because of the absence of hemodynamic disturbance. We report this case with review of literature. PMID:27347288

  18. Multiple-orifice liquid injection into hypersonic air streams.

    NASA Technical Reports Server (NTRS)

    Weaver, W. L.

    1972-01-01

    Review of oblique water and fluorocarbon injection test results obtained in experimental studies of the effects of multiple-orifice liquid injection into hypersonic air streams. The results include the finding that maximum lateral penetration from such injections increases linearly with the square root of the jet-to-freestream dynamic-pressure ratio and is proportional to an equivalent orifice diameter.

  19. Wind tunnel investigation of an all flush orifice air data system for a large subsonic aircraft. [conducted in a Langley 8 foot transonic pressure tunnel

    NASA Technical Reports Server (NTRS)

    Larson, T. J.; Flechner, S. G.; Siemers, P. M., III

    1980-01-01

    The results of a wind tunnel investigation on an all flush orifice air data system for use on a KC-135A aircraft are presented. The investigation was performed to determine the applicability of fixed all flush orifice air data systems that use only aircraft surfaces for orifices on the nose of the model (in a configuration similar to that of the shuttle entry air data system) provided the measurements required for the determination of stagnation pressure, angle of attack, and angle of sideslip. For the measurement of static pressure, additional flush orifices in positions on the sides of the fuselage corresponding to those in a standard pitot-static system were required. An acceptable but less accurate system, consisting of orifices only on the nose of the model, is defined and discussed.

  20. A Simple Model of Pulsed Ejector Thrust Augmentation

    NASA Technical Reports Server (NTRS)

    Wilson, Jack; Deloof, Richard L. (Technical Monitor)

    2003-01-01

    A simple model of thrust augmentation from a pulsed source is described. In the model it is assumed that the flow into the ejector is quasi-steady, and can be calculated using potential flow techniques. The velocity of the flow is related to the speed of the starting vortex ring formed by the jet. The vortex ring properties are obtained from the slug model, knowing the jet diameter, speed and slug length. The model, when combined with experimental results, predicts an optimum ejector radius for thrust augmentation. Data on pulsed ejector performance for comparison with the model was obtained using a shrouded Hartmann-Sprenger tube as the pulsed jet source. A statistical experiment, in which ejector length, diameter, and nose radius were independent parameters, was performed at four different frequencies. These frequencies corresponded to four different slug length to diameter ratios, two below cut-off, and two above. Comparison of the model with the experimental data showed reasonable agreement. Maximum pulsed thrust augmentation is shown to occur for a pulsed source with slug length to diameter ratio equal to the cut-off value.

  1. A numerical and experimental investigation of the flow acceleration region proximal to an orifice.

    PubMed

    Anayiotos, A S; Perry, G J; Myers, J G; Green, D W; Fan, P H; Nanda, N C

    1995-01-01

    Attempts to quantify valvular regurgitation have recently been focused on the proximal orifice flow field. A complete description of the proximal orifice flow field is provided in this investigation. A steady state in vitro model accessible by both color Doppler ultrasound (CDU) and laser Doppler velocimetry (LDV) was utilized. Velocities for varying flow rates and orifices were calculated by finite element modeling (FEM), by LDV and by CDU. The steady flow model was composed of circular orifices of 3, 5 and 10 mm diameters at flow rates from 0.7 to 10 L/min. Regurgitant flow rates were calculated from the proximal CDU data by two separate methods. The first approach utilized angle corrected velocities while the second approach utilized only velocities which did not require angle correction (centerline velocities). Both methods correlated well with known flow rates (y = 0.97x -0.09, r = 0.98, SEE = 0.45, p < 0.0001; and y = 1.0x + 0.07, r = 0.99, SEE = 0.27, p < 0.0001, respectively) and were superior to results obtained by assuming a hemispherical geometry as is done in the aliasing technique. The methodology provides a complete analysis of the proximal flow field and involves fewer geometric assumptions than the aliasing approach. This may prove to be an advantage when analyzing in vivo flow fields with complex, uncertain geometry. PMID:7571143

  2. Flows through sequential orifices with heated spacer reservoirs

    NASA Technical Reports Server (NTRS)

    Hendricks, R. C.; Stetz, T. T.

    1982-01-01

    Flow rates and pressure thermal profiles for two phase choked flows of fluid nitrogen were studied theoretically and experimentally in a four sequential orifice configuration. Both theory and experimental evidence demonstrate that heat addition in the first spacer-reservoir adjacent to the inlet orifice is most effective in reducing the flow rate and that heat addition in the last spacer-reservoir is least effective. The flows are choked at the exit orifice for large spacings and at the inlet orifice for small spacings. The moderate addition of heat available for this experiment did not materially alter this result for large spacings; however, significant heat addition for the small spacings tended to shift the choke point to the exit orifice. Nitrogen is used as the working fluid over a range of states from liquid to gas with a reduced inlet stagnation pressure range to P sub r, o = 2.

  3. How to prevent venous cannula orifice obstruction during extracorporeal circulation.

    PubMed

    Abdel-Sayed, S; Favre, J; von Segesser, L K

    2015-04-01

    Venous cannula orifice obstruction is an underestimated problem during augmented cardiopulmonary bypass (CPB), which can potentially be reduced with redesigned, virtually wall-less cannula designs versus traditional percutaneous control venous cannulas. A bench model, allowing for simulation of the vena cava with various affluent orifices, venous collapse and a worst case scenario with regard to cannula position, was developed. Flow (Q) was measured sequentially for right atrial+hepatic+renal+iliac drainage scenarios, using a centrifugal pump and an experimental bench set-up (afterload 60 mmHg). At 1500, 2000 and 2500 RPM and atrial position, the Q values were 3.4, 6.03 and 8.01 versus 0.77*, 0.43* and 0.58* l/min: p<0.05* for wall-less and the Biomedicus® cannula, respectively. The corresponding pressure values were -15.18, -31.62 and -74.53 versus -46.0*, -119.94* and -228.13* mmHg. At the hepatic position, the Q values were 3.34, 6.67 and 9.26 versus 2.3*, 0.42* and 0.18* l/min; and the pressure values were -10.32, -20.25 and -42.83 versus -23.35*, -119.09* and -239.38* mmHg. At the renal position, the Q values were 3.43, 6.56 and 8.64 versus 2.48*, 0.41* and 0.22* l/min and the pressure values were -9.64, -20.98 and -63.41 versus -20.87 -127.68* and -239* mmHg, respectively. At the iliac position, the Q values were 3.43, 6.01 and 9.25 versus 1.62*, 0.55* and 0.58* l/min; the pressure values were -9.36, -33.57 and -44.18 versus -30.6*, -120.27* and -228* mmHg, respectivly. Our experimental evaluation demonstrates that the redesigned, virtually wall-less cannulas, allowing for direct venous drainage at practically all intra-venous orifices, outperform the commercially available control cannula, with superior flow at reduced suction levels for all scenarios tested. PMID:25416743

  4. Micro-Facet Scattering Model for Pulse Polarization Ranging

    NASA Astrophysics Data System (ADS)

    Stryjewski, J.; Roggemann, M.; Tyler, D.; Hand, D.

    Determining the shape, material and orientation of nano-sats (satellites too small to image from the ground) requires new sensing approaches. Pulse Polarization Ranging (PPR) is one such approach that uses the polarization and shape characteristics of laser pulses reflected from satellites to determine satellite shape, orientation and material. We use an innovative approach to relate PPR measurements to actual satellite characteristics (shape, material and orientation), requiring that we have an accurate physical and dynamical model of the satellite. In particular, to determine the polarization characteristics (depolarization, birefringence, diattenuation) of the reflected pulses we need an accurate model of light scattering from real (complex) surfaces. To do this, we have extended the micro-facet model of Ashikhmin et al. to include retro-reflection and multiple scattering effects. In this presentation, we describe the scattering model and its efficient implementation using graphical processing units (GPUs).

  5. Use of nose cap and fuselage pressure orifices for determination of air data for space shuttle orbiter below supersonic speeds

    NASA Technical Reports Server (NTRS)

    Larson, T. J.; Siemers, P. M., III

    1980-01-01

    Wind tunnel pressure measurements were acquired from orifices on a 0.1 scale forebody model of the space shuttle orbiter that were arranged in a preliminary configuration of the shuttle entry air data system (SEADS). Pressures from those and auxiliary orifices were evaluated for their ability to provide air data at subsonic and transonic speeds. The orifices were on the vehicle's nose cap and on the sides of the forebody forward of the cabin. The investigation covered a Mach number range of 0.25 to 1.40 and an angle of attack range from 4 deg. to 18 deg. An air data system consisting of nose cap and forebody fuselage orifices constitutes a complete and accurate air data system at subsonic and transonic speeds. For Mach numbers less than 0.80 orifices confined to the nose cap can be used as a complete and accurate air data system. Air data systems that use only flush pressure orifices can be used to determine basic air data on other aircraft at subsonic and transonic speeds.

  6. Modeling of ultrashort pulse generation in mode-locked VECSELs

    NASA Astrophysics Data System (ADS)

    Kilen, I.; Koch, S. W.; Hader, J.; Moloney, J. V.

    2016-03-01

    We present a study of various models for the mode-locked pulse dynamics in a vertical external-cavity surface emitting laser with a saturable absorber. The semiconductor Bloch equations are used to model microscopically the light-matter interaction and the carrier dynamics. Maxwell's equations describe the pulse propagation. Scattering contributions due to higher order correlation effects are approximated using effective rates that are found from a comparison to solving the microscopic scattering equations on the second Born-Markov level. It is shown that the simulations result in the same mode-locked final state whether the system is initialized with a test pulse close to the final mode-locked pulse or the full field build-up from statistical noise is considered. The influence of the cavity design is studied. The longest pulses are found for a standard V-cavity while a linear cavity and a V-cavity with an high reflectivity mirror in the middle are shown to produce similar, much shorter pulses.

  7. Pulse

    MedlinePlus

    ... resting for at least 10 minutes. Take the exercise heart rate while you are exercising. ... pulse rate can help determine if the patient's heart is pumping. ... rate gives information about your fitness level and health.

  8. Modeling Escherichia coli removal in constructed wetlands under pulse loading.

    PubMed

    Hamaamin, Yaseen A; Adhikari, Umesh; Nejadhashemi, A Pouyan; Harrigan, Timothy; Reinhold, Dawn M

    2014-03-01

    Manure-borne pathogens are a threat to water quality and have resulted in disease outbreaks globally. Land application of livestock manure to croplands may result in pathogen transport through surface runoff and tile drains, eventually entering water bodies such as rivers and wetlands. The goal of this study was to develop a robust model for estimating the pathogen removal in surface flow wetlands under pulse loading conditions. A new modeling approach was used to describe Escherichia coli removal in pulse-loaded constructed wetlands using adaptive neuro-fuzzy inference systems (ANFIS). Several ANFIS models were developed and validated using experimental data under pulse loading over two seasons (winter and summer). In addition to ANFIS, a mechanistic fecal coliform removal model was validated using the same sets of experimental data. The results showed that the ANFIS model significantly improved the ability to describe the dynamics of E. coli removal under pulse loading. The mechanistic model performed poorly as demonstrated by lower coefficient of determination and higher root mean squared error compared to the ANFIS models. The E. coli concentrations corresponding to the inflection points on the tracer study were keys to improving the predictability of the E. coli removal model. PMID:24231031

  9. Model of Layered Weld Formation Under Narrow Gap Pulse Welding

    NASA Astrophysics Data System (ADS)

    Krampit, A. G.

    2016-04-01

    The model parameters of narrow gap pulse welding can be divided into input, internal and output ones. The breadth of gap, that is, clearance breadth between upright edges is one of key parameters securing high quality of a weld joint. The paper presents theoretical outcomes for the model of layered weld formation under narrow gap pulse welding. Based on these studies is developed model of processes, which occur in the weld pool under pulse grove welding. It comprises the scheme of liquid metal motion in the weld pool, scheme of fusion with the side edge and in the bottom part, and the scheme of welding current impulse effect on the structure of a weld joint.

  10. Thor: Modeling of a Megabar Class Pulsed Power Accelerator

    NASA Astrophysics Data System (ADS)

    Haill, T. A.; Reisman, D. B.; Stoltzfus, B. S.; Austin, K. N.; Stygar, W. A.; Brown, J. L.; Davis, J.-P.; Waisman, E. M.

    2015-06-01

    Thor is a compact, economical machine to drive megabar-class shockless compression material physics experiments and multi-mega-ampere HEDP experiments for the physics community. It is capable of driving peak currents up to 7 MA with rise times of 200-500 ns, resulting in material pressures between 1 to 5 Mbar depending upon the load design, and incorporates a pulse tailoring capability required to maintain shockless loading of many materials. Thor is modular in nature with 200 capacitive bricks triggered in groups by independent, de-coupled switches. The current pulse at the load is a simple linear combination of the 200 time-shifted basis pulses. This enables a variety of experiments including shockless compression experiments using smooth ramped pulses, shock-ramp compression experiments using tailored pulses, and strength measurement experiments using flat top pulses. This paper overviews the Thor design and describes an equivalent circuit model of the machine that drives MHD simulations of the load region. 3D ALEGRA MHD simulations explore topics such as the uniformity of the magnetic field along the stripline load and the design modifications to improve uniformity. Optimized current drives and simulations of the aforementioned applications are also presented. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE's NNSA under Contract DE-AC04-94AL85000.

  11. A numerical study on the effects of cavitation on orifice flow

    NASA Astrophysics Data System (ADS)

    Dabiri, S.; Sirignano, W. A.; Joseph, D. D.

    2010-04-01

    Previous experimental studies have shown better atomization of sprays generated by high-pressure liquid injectors when cavitation occurs inside the nozzle. It has been proposed that the collapse of traveling cavitation bubbles increases the disturbances inside the liquid flow. These disturbances will later trigger the instabilities in the emerged jet and cause a shorter breakup distance. In this paper, effects of cavitation on increasing the disturbances in the flow through the orifice of an atomizer are studied. In previous cavitation models, spherical cavitation bubbles are considered. Here, the cavitation bubbles are allowed to deform as they travel through the orifice. Dynamics of the cavitation bubble, traveling in the separated shear layer in the orifice, is analyzed through a one-way coupling between the orifice flow and bubble dynamics. Effects of shear strain, normal strain, and pressure variation are examined. Three mechanisms are suggested that could be responsible for the increase in disturbances in the flow due to cavitation. These mechanisms are monopole, quadrupole, and vorticities generated during growth and collapse of cavitation bubbles. The effects of these mechanisms are estimated by postprocessing of the solutions to the Navier-Stokes equations to identify monopole and quadrupole behaviors.

  12. Orifice-induced pressure error studies in Langley 7- by 10-foot high-speed tunnel

    NASA Technical Reports Server (NTRS)

    Plentovich, E. B.; Gloss, B. B.

    1986-01-01

    For some time it has been known that the presence of a static pressure measuring hole will disturb the local flow field in such a way that the sensed static pressure will be in error. The results of previous studies aimed at studying the error induced by the pressure orifice were for relatively low Reynolds number flows. Because of the advent of high Reynolds number transonic wind tunnels, a study was undertaken to assess the magnitude of this error at high Reynolds numbers than previously published and to study a possible method of eliminating this pressure error. This study was conducted in the Langley 7- by 10-Foot High-Speed Tunnel on a flat plate. The model was tested at Mach numbers from 0.40 to 0.72 and at Reynolds numbers from 7.7 x 1,000,000 to 11 x 1,000,000 per meter (2.3 x 1,000,000 to 3.4 x 1,000,000 per foot), respectively. The results indicated that as orifice size increased, the pressure error also increased but that a porous metal (sintered metal) plug inserted in an orifice could greatly reduce the pressure error induced by the orifice.

  13. Pressure atomizer having multiple orifices and turbulent generation feature

    DOEpatents

    VanBrocklin, Paul G.; Geiger, Gail E.; Moran, Donald James; Fournier, Stephane

    2002-01-01

    A pressure atomizer includes a silicon plate having a top surface and a bottom surface. A portion of the top surface defines a turbulent chamber. The turbulent chamber is peripherally bounded by the top surface of the plate. The turbulent chamber is recessed a predetermined depth relative to the top surface. The silicon plate further defines at least one flow orifice. Each flow orifice extends from the bottom surface of the silicon plate to intersect with and open into the turbulent chamber. Each flow orifice is in fluid communication with the turbulent chamber.

  14. Double-orifice mitral valve treated by percutaneous balloon valvuloplasty.

    PubMed

    Varghese, Thomas George; Revankar, Vinod Raghunath; Papanna, Monica; Srinivasan, Harshini

    2016-07-01

    Double-orifice mitral valve is an rare anomaly characterized by a mitral valve with a single fibrous annulus and 2 orifices that open into the left ventricle. It is often associated with other congenital anomalies, most commonly atrioventricular canal defects, and rarely associated with a stenotic or regurgitant mitral valve. A patient who was diagnosed with congenital double-orifice mitral valve with severe mitral stenosis was treated successfully by percutaneous balloon mitral valvotomy rather than the conventional open surgical approach, demonstrating the utility of percutaneous correction of this anomaly. PMID:26045488

  15. Increasing pulse wave velocity in a realistic cardiovascular model does not increase pulse pressure with age.

    PubMed

    Mohiuddin, Mohammad W; Rihani, Ryan J; Laine, Glen A; Quick, Christopher M

    2012-07-01

    The mechanism of the well-documented increase in aortic pulse pressure (PP) with age is disputed. Investigators assuming a classical windkessel model believe that increases in PP arise from decreases in total arterial compliance (C(tot)) and increases in total peripheral resistance (R(tot)) with age. Investigators assuming a more sophisticated pulse transmission model believe PP rises because increases in pulse wave velocity (c(ph)) make the reflected pressure wave arrive earlier, augmenting systolic pressure. It has recently been shown, however, that increases in c(ph) do not have a commensurate effect on the timing of the reflected wave. We therefore used a validated, large-scale, human arterial system model that includes realistic pulse wave transmission to determine whether increases in c(ph) cause increased PP with age. First, we made the realistic arterial system model age dependent by altering cardiac output (CO), R(tot), C(tot), and c(ph) to mimic the reported changes in these parameters from age 30 to 70. Then, c(ph) was theoretically maintained constant, while C(tot), R(tot), and CO were altered. The predicted increase in PP with age was similar to the observed increase in PP. In a complementary approach, C(tot), R(tot), and CO were theoretically maintained constant, and c(ph) was increased. The predicted increase in PP was negligible. We found that increases in c(ph) have a limited effect on the timing of the reflected wave but cause the system to degenerate into a windkessel. Changes in PP can therefore be attributed to a decrease in C(tot). PMID:22561301

  16. Periodic cavitation shedding in a cylindrical orifice

    NASA Astrophysics Data System (ADS)

    Stanley, C.; Barber, T.; Milton, B.; Rosengarten, G.

    2011-11-01

    Cavitation structures in a large-scale ( D = 8.25 mm), plain orifice style nozzle within a unique experimental rig are investigated using high-speed visualisation and digital image processing techniques. Refractive index matching with an acrylic nozzle is achieved using aqueous sodium iodide for the test fluid. Cavitation collapse length, unsteady shedding frequency and spray angles are measured for cavitation conditions from incipient to supercavitation for a range of Reynolds numbers, for a fixed L/ D ratio of 4.85. Periodic cavitation shedding was shown to occur with frequencies between 500 and 2,000 Hz for conditions in which cavitation occupied less than 30% of the nozzle length. A discontinuity in collapse length was shown to occur once the cavitation exceeded this length, coinciding with a loss of periodic shedding. A mechanism for this behaviour is discussed. Peak spray angles of approximately θ ≈ 14° were recorded for supercavitation conditions indicating the positive influence of cavitation bubble collapse on the jet atomisation process.

  17. Modeling and simulation of ultra-short pulse amplification

    NASA Astrophysics Data System (ADS)

    Pflaum, Christoph; Hartmann, Rainer; Rahimi, Zhabiz

    2016-03-01

    Ultra-short pulses with high average power are required for a variety of technical and medical applications. Single, multi-pass, and regenerative amplifiers are used, in order to increase the power of ultra-short lasers. Typical laser crystals for such amplifiers include Ti:Sapphire or Yb:YAG laser crystals. Difficulties in the amplification of ultra-short pulses include gain narrowing effects and dispersion effects in the laser crystal. In particular, these complications arise, when a pulse stretcher is needed before amplification of the laser beam. We present a technique to model and simulate the amplification of ultra-short pulses. This technique allows to model both gain narrowing effects and decrease of beam quality caused by amplification of the laser beam. This requires a detailed 3-dimensional simulation of population inversion. Gain narrowing effects are taken into account by analyzing the gain of the spectrum of the laser beam. It is important to distinguish amplifiers with one or only two passes and a regenerative amplifier. These two different kind of amplifiers are modeled by different approaches. A regenerative amplifier is modeled by a set of time dependent rate equations. However, a single pass amplifier is modeled by a set of spatial dependent rate equations. In both cases, a system of rate equations arises from spectral discretization of the laser beam. Detailed simulation results are presented.

  18. Quasi-One-Dimensional Modeling of Pulse Detonation Rocket Engines

    NASA Technical Reports Server (NTRS)

    Morris, Christopher I.

    2003-01-01

    Pulse detonation rocket engines (PDREs) offer potential performance improvements over conventional designs, but represent a challenging modeling task. A quasi 1-D, finite-rate chemistry CFD model for a PDRE & described and implemented. A parametric study of the effect of blowdown pressure ratio on the performance of an optimized, fixed PDRE nozzle configuration is reported. The results are compared to a steady-state rocket system using similar modeling assumptions.

  19. State dependent model predictive control for orbital rendezvous using pulse-width pulse-frequency modulated thrusters

    NASA Astrophysics Data System (ADS)

    Li, Peng; Zhu, Zheng H.; Meguid, S. A.

    2016-07-01

    This paper studies the pulse-width pulse-frequency modulation based trajectory planning for orbital rendezvous and proximity maneuvering near a non-cooperative spacecraft in an elliptical orbit. The problem is formulated by converting the continuous control input, output from the state dependent model predictive control, into a sequence of pulses of constant magnitude by controlling firing frequency and duration of constant-magnitude thrusters. The state dependent model predictive control is derived by minimizing the control error of states and control roughness of control input for a safe, smooth and fuel efficient approaching trajectory. The resulting nonlinear programming problem is converted into a series of quadratic programming problem and solved by numerical iteration using the receding horizon strategy. The numerical results show that the proposed state dependent model predictive control with the pulse-width pulse-frequency modulation is able to effectively generate optimized trajectories using equivalent control pulses for the proximity maneuvering with less energy consumption.

  20. Model for nonequilibrium segregation during pulsed laser annealing

    SciTech Connect

    Wood, R.F.

    1980-08-01

    Highly nonequilibrium thermodynamic processes occur during the ultrarapid recrystallization characteristic of pulsed laser annealing. Values of interface segregation coefficients are observed to differ from equilibrium values by as much as three orders of magnitude and equilibrium solubility limits may be exceeded by similar magnitudes. In this letter, a model is developed which accounts quantitatively for these effects.

  1. Acute inflammatory response to transgastric natural orifice transluminal endoscopic surgery peritoneoscopy: An experimental study in swine

    PubMed Central

    Rezende, Marcelo; Montero, Edna Frasson de Souza; Salomão, Reinaldo; Brunialti, Milena; Rodrigues, Rodrigo; Gomes, Gustavo; Libera, Alice Della; Ferrari, Angelo; Libera, Ermelindo Della

    2013-01-01

    OBJECTIVE: To investigate the impact of transgastric peritoneal access on plasma biomarkers of acute inflammatory response in comparison to laparoscopy. METHODS: This was a prospective and comparative study in a porcine model. Transgastric peritoneal access performed by natural orifice transluminal endoscopic surgery was compared with laparoscopy. Laparotomy and sham groups were used as positive and negative controls, respectively. Thirty-four pigs were assigned to receive transgastric natural orifice transluminal endoscopic surgery (n = 12), laparoscopy (n = 8), laparotomy (n = 8) or a sham procedure involving only anesthesia (n = 6). In the natural orifice transluminal endoscopic surgery group, peritoneoscopy was performed with a gastroscope via transgastric access. Blood samples were collected at baseline and 1, 3, 6, 9 and 24 h after the surgical procedure for measurement of interleukins 1β, 6 and 10 and tumor necrosis factor-α. A complete blood count was performed, and C-reactive protein levels were measured at baseline and at 24 h. RESULTS: All surgical and endoscopic procedures were performed without major complications. Peritoneal cavity inventory showed no signs of peritonitis in any animal. Interleukin 1β, interleukin 10 and tumor necrosis factor-α levels were below the threshold of detection. The mean level of interleukin 6 was statistically significantly higher in the laparotomy group than in the other groups (p<0.05), with no significant differences among the sham, laparoscopy and natural orifice transluminal endoscopic surgery groups (p>0.05). C-reactive protein analysis indicated significant increases in all groups, with no differences among the groups. Complete blood count analysis showed no differences among the groups. CONCLUSIONS: Based on the observed interleukin 6 patterns, the systemic inflammatory response resulting from transgastric peritoneal access by natural orifice transluminal endoscopic surgery is similar in

  2. Numerical Modeling of Pulse Detonation Rocket Engine Gasdynamics and Performance

    NASA Technical Reports Server (NTRS)

    Morris, C. I.

    2003-01-01

    Pulse detonation engines (PDB) have generated considerable research interest in recent years as a chemical propulsion system potentially offering improved performance and reduced complexity compared to conventional gas turbines and rocket engines. The detonative mode of combustion employed by these devices offers a theoretical thermodynamic advantage over the constant-pressure deflagrative combustion mode used in conventional engines. However, the unsteady blowdown process intrinsic to all pulse detonation devices has made realistic estimates of the actual propulsive performance of PDES problematic. The recent review article by Kailasanath highlights some of the progress that has been made in comparing the available experimental measurements with analytical and numerical models.

  3. 49 CFR 230.71 - Orifice testing of compressors.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... Compressor size Single strokes per minute Diameter of orifice(in inches) Air pressure maintained(in pounds... feet the speed of compressor may be increased 5 single strokes per minute for each 1,000 feet...

  4. 49 CFR 230.71 - Orifice testing of compressors.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... Compressor size Single strokes per minute Diameter of orifice(in inches) Air pressure maintained(in pounds... feet the speed of compressor may be increased 5 single strokes per minute for each 1,000 feet...

  5. ETF Facility evaporator skid orifice sizing design analysis

    SciTech Connect

    ELLINGSON, S.D.

    1999-08-31

    This document releases and records the design analysis for sizing the Orifice plate being installed on the Effluent Treatment Facility (ETF) evaporator skid per Engineering Change Notice (ECN) 651583.

  6. Fabrication of small-orifice fuel injectors for diesel engines.

    SciTech Connect

    Woodford, J. B.; Fenske, G. R.

    2005-04-08

    Diesel fuel injector nozzles with spray hole diameters of 50-75 {micro}m have been fabricated via electroless nickel plating of conventionally made nozzles. Thick layers of nickel are deposited onto the orifice interior surfaces, reducing the diameter from {approx}200 {micro}m to the target diameter. The nickel plate is hard, smooth, and adherent, and covers the orifice interior surfaces uniformly.

  7. Stalled Pulsing Inertial Oscillation Model for a Tornadic Cyclone

    NASA Technical Reports Server (NTRS)

    Costen, Robert C.

    2005-01-01

    A supercell storm is a tall, rotating thunderstorm that can generate hail and tornadoes. Two models exist for the development of the storm's rotation or mesocyclone - the conventional splitting-storm model, and the more recent pulsing inertial oscillation (PIO) model, in which a nonlinear pulse represents the supercell. Although data support both models and both could operate in the same supercell, neither model has satisfactorily explained the tornadic cyclone. A tornadic cyclone is an elevated vorticity concentration of Rossby number approximately 1000 that develops within the contracting mesocyclone shortly before a major tornado appears at the surface. We now show that if the internal temperature excess due to latent energy release is limited to the realistic range of -12 K to +12 K, the PIO model can stall part way through the pulse in a state of contraction and spin-up. Should this happen, the stalled-PIO model can evolve into a tornadic cyclone with a central pressure deficit that exceeds 40 mb, which is greater than the largest measured value. This simulation uses data from a major tornadic supercell that occurred over Oklahoma City, Oklahoma, USA, on May 3, 1999. The stalled-PIO mechanism also provides a strategy for human intervention to retard or reverse the development of a tornadic cyclone and its pendant tornado.

  8. Block-Based Neural Networks with Pulsed Neuron Model

    NASA Astrophysics Data System (ADS)

    Iguchi, Syota; Koakutsu, Seiichi; Okamoto, Takashi; Hirata, Hironori

    In recent years, the study of hardware implementation of Neural Networks (NN) has been getting more important. In particular, Block-Based Neural Networks (BBNN) which are one of NN have been attracted attention. However, the conventional BBNN are analogue NN (ANN). The digital hardware implementation of ANN is very difficult, because the input and output signals are represented as analogue values. Pulsed Neural Networks (PNN) which adopt a pulsed neuron (PN) model instead of the AN model have been proposed in order to solve this problem. The input and output signals of PNN are represented as a series of pulses, and thus the digital hardware implementation of PNN becomes easy. In this paper, we propose Block-Based Pulsed Neural Networks (BBPNN) introducing the PN model into BBNN in order to faciliate the implementation of NN on digital hardware. We use particle swarm optimization (PSO) for optimization of weights of BBPNN, because PSO can produce a globally optimum solution of nonlinear continuous optimization problems in practicable calculation time by high accuracy. To evaluate the proposed BBPNN, we apply them to XOR problem and autonomous mobile robot control problems. Computational experiments indicate that the proposed BBPNN and the conventional BBNN can produce about the same results.

  9. Computational Modeling of Ultrafast Pulse Propagation in Nonlinear Optical Materials

    NASA Technical Reports Server (NTRS)

    Goorjian, Peter M.; Agrawal, Govind P.; Kwak, Dochan (Technical Monitor)

    1996-01-01

    There is an emerging technology of photonic (or optoelectronic) integrated circuits (PICs or OEICs). In PICs, optical and electronic components are grown together on the same chip. rib build such devices and subsystems, one needs to model the entire chip. Accurate computer modeling of electromagnetic wave propagation in semiconductors is necessary for the successful development of PICs. More specifically, these computer codes would enable the modeling of such devices, including their subsystems, such as semiconductor lasers and semiconductor amplifiers in which there is femtosecond pulse propagation. Here, the computer simulations are made by solving the full vector, nonlinear, Maxwell's equations, coupled with the semiconductor Bloch equations, without any approximations. The carrier is retained in the description of the optical pulse, (i.e. the envelope approximation is not made in the Maxwell's equations), and the rotating wave approximation is not made in the Bloch equations. These coupled equations are solved to simulate the propagation of femtosecond optical pulses in semiconductor materials. The simulations describe the dynamics of the optical pulses, as well as the interband and intraband.

  10. 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.

  11. Broadband spatiotemporal Gaussian Schell-model pulse trains.

    PubMed

    Dutta, Rahul; Korhonen, Minna; Friberg, Ari T; Genty, Göery; Turunen, Jari

    2014-03-01

    A new class of partially coherent model sources is introduced on the basis of the second-order coherence theory of nonstationary optical fields. These model sources are spatially fully coherent at each frequency but can have broadband spectra and variable spectral coherence properties, which lead to reduced spatiotemporal coherence in the time domain. The source model is motivated by the spectral coherence properties of supercontinuum pulse trains generated in single-spatial-mode optical fibers. We demonstrate that such broadband light is highly (but not completely) spatially coherent, even though the spectral and temporal coherence properties may vary over a wide range. The model sources introduced here are convenient in assessing the spatiotemporal coherence of broadband pulses in optical systems. PMID:24690663

  12. Apparatus for depositing hard coating in a nozzle orifice

    DOEpatents

    Flynn, P.L.; Giammarise, A.W.

    1995-02-21

    The present invention is directed to a process for coating the interior surfaces of an orifice in a substrate that forms a slurry fuel injection nozzle. In a specific embodiment, the nozzle is part of a fuel injection system for metering a coal-water slurry into a large, medium-speed, multi-cylinder diesel engine. In order to retard erosion of the orifice, the substrate is placed in a chemical vapor deposition (CVD) reaction chamber. A reaction gas is passed into the chamber at a gas temperature below its reaction temperature and is directed through the orifice in the substrate. The gas reaction temperature is a temperature at and above which the reaction gas deposits as a coating, and the reaction gas is of a composition whereby improved resistance to erosion by flow of the particulates in the slurry fuel is imparted by the deposited coating. Only the portion of the substrate in proximity to the orifice to be coated is selectively heated to at least the gas reaction temperature for effecting coating of the orifice`s interior surfaces by the vapor deposited coating formed from the reaction gas. 2 figs.

  13. Advanced modeling techniques in application to plasma pulse treatment

    NASA Astrophysics Data System (ADS)

    Pashchenko, A. F.; Pashchenko, F. F.

    2016-06-01

    Different approaches considered for simulation of plasma pulse treatment process. The assumption of a significant non-linearity of processes in the treatment of oil wells has been confirmed. Method of functional transformations and fuzzy logic methods suggested for construction of a mathematical model. It is shown, that models, based on fuzzy logic are able to provide a satisfactory accuracy of simulation and prediction of non-linear processes observed.

  14. Modelling Multi-Pulse Population Dynamics from Ultrafast Spectroscopy

    PubMed Central

    van Wilderen, Luuk J. G. W.; Lincoln, Craig N.; van Thor, Jasper J.

    2011-01-01

    Current advanced laser, optics and electronics technology allows sensitive recording of molecular dynamics, from single resonance to multi-colour and multi-pulse experiments. Extracting the occurring (bio-) physical relevant pathways via global analysis of experimental data requires a systematic investigation of connectivity schemes. Here we present a Matlab-based toolbox for this purpose. The toolbox has a graphical user interface which facilitates the application of different reaction models to the data to generate the coupled differential equations. Any time-dependent dataset can be analysed to extract time-independent correlations of the observables by using gradient or direct search methods. Specific capabilities (i.e. chirp and instrument response function) for the analysis of ultrafast pump-probe spectroscopic data are included. The inclusion of an extra pulse that interacts with a transient phase can help to disentangle complex interdependent pathways. The modelling of pathways is therefore extended by new theory (which is included in the toolbox) that describes the finite bleach (orientation) effect of single and multiple intense polarised femtosecond pulses on an ensemble of randomly oriented particles in the presence of population decay. For instance, the generally assumed flat-top multimode beam profile is adapted to a more realistic Gaussian shape, exposing the need for several corrections for accurate anisotropy measurements. In addition, the (selective) excitation (photoselection) and anisotropy of populations that interact with single or multiple intense polarised laser pulses is demonstrated as function of power density and beam profile. Using example values of real world experiments it is calculated to what extent this effectively orients the ensemble of particles. Finally, the implementation includes the interaction with multiple pulses in addition to depth averaging in optically dense samples. In summary, we show that mathematical modelling is

  15. Pulsed pumping process optimization using a potential flow model.

    PubMed

    Tenney, C M; Lastoskie, C M

    2007-08-15

    A computational model is applied to the optimization of pulsed pumping systems for efficient in situ remediation of groundwater contaminants. In the pulsed pumping mode of operation, periodic rather than continuous pumping is used. During the pump-off or trapping phase, natural gradient flow transports contaminated groundwater into a treatment zone surrounding a line of injection and extraction wells that transect the contaminant plume. Prior to breakthrough of the contaminated water from the treatment zone, the wells are activated and the pump-on or treatment phase ensues, wherein extracted water is augmented to stimulate pollutant degradation and recirculated for a sufficient period of time to achieve mandated levels of contaminant removal. An important design consideration in pulsed pumping groundwater remediation systems is the pumping schedule adopted to best minimize operational costs for the well grid while still satisfying treatment requirements. Using an analytic two-dimensional potential flow model, optimal pumping frequencies and pumping event durations have been investigated for a set of model aquifer-well systems with different well spacings and well-line lengths, and varying aquifer physical properties. The results for homogeneous systems with greater than five wells and moderate to high pumping rates are reduced to a single, dimensionless correlation. Results for heterogeneous systems are presented graphically in terms of dimensionless parameters to serve as an efficient tool for initial design and selection of the pumping regimen best suited for pulsed pumping operation for a particular well configuration and extraction rate. In the absence of significant retardation or degradation during the pump-off phase, average pumping rates for pulsed operation were found to be greater than the continuous pumping rate required to prevent contaminant breakthrough. PMID:17350717

  16. Creating Small Gas Bubbles in Flowing Mercury Using Turbulence at an Orifice

    SciTech Connect

    Wendel, Mark W; Abdou, Ashraf A; Paquit, Vincent C; Felde, David K; Riemer, Bernie

    2010-01-01

    Pressure waves created in liquid mercury pulsed spallation targets have been shown to create cavitation damage to the target container. One way to mitigate such damage would be to absorb the pressure pulse energy into a dispersed population of small bubbles, however, creating such a population in mercury is difficult due to the high surface tension and particularly the non-wetting behavior of mercury on gas-injection hardware. If the larger injected gas bubbles can be broken down into small bubbles after they are introduced to the flow, then the material interface problem is avoided. Research at the Oak Ridge National Labarotory is underway to develop a technique that has shown potential to provide an adequate population of small-enough bubbles to a flowing spallation target. This technique involves gas injection at an orifice of a geometry that is optimized to the turbulence intensity and pressure distribution of the flow, while avoiding coalescence of gas at injection sites. The most successful geometry thus far can be described as a square-toothed orifice having a 2.5 bar pressure drop in the nominal flow of 12 L/s for one of the target inlet legs. High-speed video and high-resolution photography have been used to quantify the bubble population on the surface of the mercury downstream of the gas injection sight. Also, computational fluid dynamics has been used to optimize the dimensions of the toothed orifice based on a RANS computed mean flow including turbulent energies such that the turbulent dissipation and pressure field are best suited for turbulent break-up of the gas bubbles.

  17. Computer modeling of pulsed CO2 lasers for lidar applications

    NASA Technical Reports Server (NTRS)

    Spiers, Gary D.

    1993-01-01

    The object of this effort is to develop code to enable the accurate prediction of the performance of pulsed transversely excited (TE) CO2 lasers prior to their construction. This is of particular benefit to the NASA Laser Atmospheric Wind Sounder (LAWS) project. A benefit of the completed code is that although developed specifically for the pulsed CO2 laser much of the code can be modified to model other laser systems of interest to the lidar community. A Boltzmann equation solver has been developed which enables the electron excitation rates for the vibrational levels of CO2 and N2, together with the electron ionization and attachment coefficients to be determined for any CO2 laser gas mixture consisting of a combination of CO2, N2, CO, He and CO. The validity of the model has been verified by comparison with published material. The results from the Boltzmann equation solver have been used as input to the laser kinetics code which is currently under development. A numerical code to model the laser induced medium perturbation (LIMP) arising from the relaxation of the lower laser level has been developed and used to determine the effect of LIMP on the frequency spectrum of the LAWS laser output pulse. The enclosed figures show representative results for a laser operating at 0.5 atm. with a discharge cross-section of 4.5 cm to produce a 20 J pulse with aFWHM of 3.1 microns. The first four plots show the temporal evolution of the laser pulse power, energy evolution, LIMP frequency chirp and electric field magnitude. The electric field magnitude is taken by beating the calculated complex electric field and beating it with a local oscillator signal. The remaining two figures show the power spectrum and energy distribution in the pulse as a function of the varying pulse frequency. The LIMP theory has been compared with experimental data from the NOAA Windvan Lidar and has been found to be in good agreement.

  18. Practitioner's guide to laser pulse propagation models and simulation. Numerical implementation and practical usage of modern pulse propagation models

    NASA Astrophysics Data System (ADS)

    Couairon, A.; Brambilla, E.; Corti, T.; Majus, D.; de J. Ramírez-Góngora, O.; Kolesik, M.

    2011-11-01

    The purpose of this article is to provide practical introduction into numerical modeling of ultrashort optical pulses in extreme nonlinear regimes. The theoretic background section covers derivation of modern pulse propagation models starting from Maxwell's equations, and includes both envelope-based models and carrier-resolving propagation equations. We then continue with a detailed description of implementation in software of Nonlinear Envelope Equations as an example of a mixed approach which combines finite-difference and spectral techniques. Fully spectral numerical solution methods for the Unidirectional Pulse Propagation Equation are discussed next. The modeling part of this guide concludes with a brief introduction into efficient implementations of nonlinear medium responses. Finally, we include several worked-out simulation examples. These are mini-projects designed to highlight numerical and modeling issues, and to teach numerical-experiment practices. They are also meant to illustrate, first and foremost for a non-specialist, how tools discussed in this guide can be applied in practical numerical modeling.

  19. Numerical Modelling of Pulse Combustor Tail Pipe Heat Transfer.

    NASA Astrophysics Data System (ADS)

    Thyageswaran, Sridhar

    1994-01-01

    Computational fluid dynamics analysis was used to perform multi-dimensional simulations of flow in a pulse combustor tail pipe. The tail pipe flow is complicated by periodic reversals amid large rates of turbulent heat transfer. The primary objectives were to understand the mechanisms causing heat transfer enhancement under pulsing flow conditions, and to develop a flow-based model capable of predicting heat transfer rates over a broad range of operating conditions. The experiments of Dec et al. (Combustion and Flame, 77, 80 and 83), in a square cross-section tail pipe, were used as the reference. The research focussed on modelling the near-wall turbulence transport, by treating the tail pipe as a two-dimensional channel. An experimental baseline pulsing case was simulated using the wall-function model, and an alternative near -wall turbulence model known as the Boundary Layer Wall Model. The latter uses an algebraically prescribed wall layer turbulence length scale, and allows much greater phase resolution between the near-wall and the bulk flow. Heat transfer predictions from these quasi-steady models compare poorly with the time-resolved measurements, and fail to match the observed increase in the instantaneous heat transfer during times of flow reversal. An unsteady wall layer model, with a robust prescription for the length scale damping factor, A^ {+}, was developed. Allowing A ^{+} to vary with the wall layer parameter, u^{+}p ^{+}, helps to model the effects of adverse and favourable pressure gradients on the wall layer turbulence during a pulsation cycle. A sequence of lag equations is also used, to incorporate the delayed response of the wall layer turbulence to the time-varying pressure gradient. Simulations of many operating conditions, spanning a range of pulsation frequencies, amplitudes and mean flow Reynolds numbers, indicate that the improved model is capable of capturing the essential trends observed by Dec et al.

  20. Computer modeling of pulsed CO2 lasers for lidar applications

    NASA Technical Reports Server (NTRS)

    Spiers, Gary D.; Smithers, Martin E.; Murty, Rom

    1991-01-01

    The experimental results will enable a comparison of the numerical code output with experimental data. This will ensure verification of the validity of the code. The measurements were made on a modified commercial CO2 laser. Results are listed as following. (1) The pulse shape and energy dependence on gas pressure were measured. (2) The intrapulse frequency chirp due to plasma and laser induced medium perturbation effects were determined. A simple numerical model showed quantitative agreement with these measurements. The pulse to pulse frequency stability was also determined. (3) The dependence was measured of the laser transverse mode stability on cavity length. A simple analysis of this dependence in terms of changes to the equivalent fresnel number and the cavity magnification was performed. (4) An analysis was made of the discharge pulse shape which enabled the low efficiency of the laser to be explained in terms of poor coupling of the electrical energy into the vibrational levels. And (5) the existing laser resonator code was changed to allow it to run on the Cray XMP under the new operating system.

  1. Modeling of Multi-Tube Pulse Detonation Engine Operation

    NASA Technical Reports Server (NTRS)

    Ebrahimi, Houshang B.; Mohanraj, Rajendran; Merkle, Charles L.

    2001-01-01

    The present paper explores some preliminary issues concerning the operational characteristics of multiple-tube pulsed detonation engines (PDEs). The study is based on a two-dimensional analysis of the first-pulse operation of two detonation tubes exhausting through a common nozzle. Computations are first performed to assess isolated tube behavior followed by results for multi-tube flow phenomena. The computations are based on an eight-species, finite-rate transient flow-field model. The results serve as an important precursor to understanding appropriate propellant fill procedures and shock wave propagation in multi-tube, multi-dimensional simulations. Differences in behavior between single and multi-tube PDE models are discussed, The influence of multi-tube geometry and the preferred times for injecting the fresh propellant mixture during multi-tube PDE operation are studied.

  2. Transient analysis of single stage GM type double inlet pulse tube cryocooler

    NASA Astrophysics Data System (ADS)

    Gujarati, P. B.; Desai, K. P.; Naik, H. B.; Atrey, M. D.

    2015-12-01

    Transient analysis of single stage GM type double inlet pulse tube cryocooler is carried out using a one dimensional numerical model based on real gas properties of helium. The model solves continuity, momentum and energy equation for gas and solid to analyse the physical process occurring inside of the pulse tube cryocooler. Finite volume method is applied to discretize the governing equations with realistic initial and boundary conditions. Input data required for solving the model are the design data and operating parameters viz. pressure waveform from the compressor, regenerator matrix data, and system geometry including pulse tube, regenerator size and operating frequency for pulse tube cryocooler. The model investigates the effect of orifice opening, double inlet opening, pressure ratio, system geometry on no load temperature and refrigeration power at various temperatures for different charging pressure. The results are compared with experimental data and reasonable agreement is observed. The model can further be extended for designing two stage pulse tube cryocooler.

  3. Modeling of Pulses in Terrestrial Gamma-ray Flashes

    NASA Astrophysics Data System (ADS)

    Xu, Wei; Celestin, Sebastien; Pasko, Victor

    2015-04-01

    Terrestrial Gamma-ray Flashes (TGFs) are high-energy photon bursts originating from the Earth's atmosphere that are associated with lightning activities. After their discovery in 1994 by the Burst and Transient Source Experiment (BATSE) detector aboard the Compton Gamma-Ray Observatory [Fishman et al., Science, 264, 1313, 1994], this phenomenon has been further observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) [Smith et al., Science, 307, 1085, 2005], the Fermi Gamma-ray Space Telescope [Briggs et al., JGR, 115, A07323, 2010] and the Astrorivelatore Gamma a Immagini Leggero (AGILE) satellite [Marisaldi et al., JGR, 115, A00E13, 2010]. Photon spectra corresponding to the mechanism of relativistic runaway electron avalanches (RREAs) usually provide a very good agreement with satellite observations [Dwyer and Smith, GRL, 32, L22804, 2005]. On the other hand, Celestin and Pasko [JGR, 116, A03315, 2011] have shown theoretically that the large flux of thermal runaway electrons generated by streamers during the negative corona flash stage of stepping lightning leaders in intracloud lightning flashes could be responsible for TGFs. Recently, based on analysis of the temporal profiles of 278 TGF events observed by the Fermi Gamma-Ray Burst Monitor, Foley et al. [JGR, 119, 5931, 2014] have suggested that 67% of TGF pulses detected are asymmetric and these asymmetric pulses are consistent with the production mechanism of TGFs by relativistic feedback discharges. In the present work, we employ a Monte Carlo model to study the temporal distribution of photons at low-orbit satellite altitudes during TGF events. Using the pulse fitting method described in [Foley et al., 2014], we further investigate the characteristics of TGF pulses. We mainly focus on the effects of Compton scattering on the symmetry properties and the rise and fall times of TGF pulses.

  4. Process for depositing hard coating in a nozzle orifice

    DOEpatents

    Flynn, P.L.; Giammarise, A.W.

    1991-10-29

    The present invention is directed to a process for coating the interior surfaces of an orifice in a substrate that forms a slurry fuel injection nozzle. In a specific embodiment, the nozzle is part of a fuel injection system for metering a coal-water slurry into a large, medium-speed, multi-cylinder diesel engine. In order to retard erosion of the orifice, the substrate is placed in a chemical vapor deposition (CVD) reaction chamber. A reaction gas is passed into the chamber at a gas temperature below its reaction temperature and is directed through the orifice in the substrate. The gas reaction temperature is a temperature at and above which the reaction gas deposits as a coating, and the reaction gas is of a composition whereby improved resistance to erosion by flow of the particulates in the slurry fuel is imparted by the deposited coating. Only the portion of the substrate in proximity to the orifice to be coated is selectively heated to at least the gas reaction temperature for effecting coating of the orifice's interior surfaces by the vapor deposited coating formed from the reaction gas. 2 figures.

  5. Apparatus for depositing hard coating in a nozzle orifice

    DOEpatents

    Flynn, Paul L.; Giammarise, Anthony W.

    1995-01-01

    The present invention is directed to a process for coating the interior surfaces of an orifice in a substrate that forms a slurry fuel injection nozzle. In a specific embodiment, the nozzle is part of a fuel injection system for metering a coal-water slurry into a large, medium-speed, multi-cylinder diesel engine. In order to retard erosion of the orifice, the substrate is placed in a chemical vapor deposition (CVD) reaction chamber. A reaction gas is passed into the chamber at a gas temperature below its reaction temperature and is directed through the orifice in the substrate. The gas reaction temperature is a temperature at and above which the reaction gas deposits as a coating, and the reaction gas is of a composition whereby improved resistance to erosion by flow of the particulates in the slurry fuel is imparted by the deposited coating. Only the portion of the substrate in proximity to the orifice to be coated is selectively heated to at least the gas reaction temperature for effecting coating of the orifice's interior surfaces by the vapor deposited coating formed from the reaction gas.

  6. Process for depositing hard coating in a nozzle orifice

    DOEpatents

    Flynn, Paul L.; Giammarise, Anthony W.

    1991-01-01

    The present invention is directed to a process for coating the interior surfaces of an orifice in a substrate that forms a slurry fuel injection nozzle. In a specific embodiment, the nozzle is part of a fuel injection system for metering a coal-water slurry into a large, medium-speed, multi-cylinder diesel engine. In order to retard erosion of the orifice, the substrate is placed in a chemical vapor deposition (CVD) reaction chamber. A reaction gas is passed into the chamber at a gas temperature below its reaction temperature and is directed through the orifice in the substrate. The gas reaction temperature is a temperature at and above which the reaction gas deposits as a coating, and the reaction gas is of a composition whereby improved resistance toerosion by flow of the particulates in the slurry fuel is imparted by the deposited coating. Only the portion of the substrate in proximity to the orifice to be coated is selectively heated to at least the gas reaction temperature for effecting coating of the orifice's interior surfaces by the vapor deposited coating formed from the reaction gas.

  7. The effect of mitral orifice eccentricity on the left ventricular hemodynamics

    NASA Astrophysics Data System (ADS)

    Le, Trung; Sotiropoulos, Fotis

    2011-11-01

    We investigate the left ventricular hemodynamics using high resolution Direct Numerical Simulation. The LV geometry is reconstructed from Magnetic Resonance Imaging (MRI) data of a healthy volunteer. The diastolic kinematics of the LV wall is modelled using a cell-based electrical activation methodology, which yields global left-heart motion parameters well within the physiologic range of an adult. By prescribing the kinematics and the physiologic mitral valve waveform, numerical simulations are carried out to investigate the intraventricular flow patterns during the diastolic filling. The results show that the intraventricular flow is dominated by the formation and breakdown of a vortex ring originating from the mitral orifice. The eccentricity of the mitral orifice is found to be the determining factor controlling the dynamics of vortex formation and rotational flow patterns at the end of diastole. This work was supported by NIH Grant RO1-HL-07262 and the Minnesota Supercomputing Institute.

  8. Study of subcritical flow through multiple-orifice valves

    SciTech Connect

    Surbey, D.W.; Kelkar, B.G.; Brill, J.P.

    1988-02-01

    Increased oil and gas production from offshore areas and hostile environments has led to a greater use of multiple-orifice-valve (MOV) wellhead chokes. Unlike conventional wellhead chokes, MOV's can be adjusted to any given choke area while under pressure, allowing wells in remote locations to be controlled from a central site. Data on the behavior of multiphase flow through MOV chokes have not been available in the past. This study investigated high-pressure (400 to 800 psia (2.8 to 5.5 MPa)), two-phase air/water flow through a 2-in. (5.1-cm) MOV choke. Single-phase air and water data were obtained to determine the valve-sizing coefficient, C/sub v/. A correlating parameter was determined with two-phase data to predict the subcritical two-phase pressure drop. This parameter was found to be a function of the gas/liquid ratio, upstream pressure, and choke opening. A mathematical model based on experimental observations was developed to predict the subcritical pressure drop across the choke for single-phase liquid flow.

  9. An analysis of Freedman's "image pulse" model in air.

    PubMed

    Tsakiris, J; McKerrow, P

    2000-10-01

    The "image pulse" model developed by Freedman calculates the echoes generated from convex objects in an underwater environment after insonification with a narrow-band transient signal. The model uses the source radiation and the solid angle subtended at the transducer by the scattering body to determine the echo structure. Work has been completed in adapting this model for use in an air environment using noncoincident transmitters and receivers. Experiments were conducted to measure the amplitudes of the echoes off a range of convex objects, at distances up to 1.4 m, after insonification with a Polaroid transducer. These measured amplitudes were compared to those predicted by the model, with the results for cones highlighting the limitations of the model. Spheres, however, performed significantly better, with an average error of under 5%, indicating that the model should be reasonably accurate at calculating the echoes off convex objects with a smoothly varying surface. PMID:11051488

  10. Impact of the QPO models on the pulse profile

    NASA Astrophysics Data System (ADS)

    Varniere, P.; Vincent, F. H.

    2015-12-01

    Quasi-periodic oscillations (QPO) are an important probe of the timing properties of black-hole binaries. Many models are proposed in order to account for these features and it is difficult to differentiate them with current data. Here we aim to look at the actual pulse profile from each model in order to see how they could be differentiated and what kind of sources are the best targets for such a test. We consider three classes of simple models: elongated hot spots, tori and spirals. We perturb the equilibrium temperature of a thin disk to create these structures. The perturbed disk is supposed to emit blackbody radiation at the local temperature. Radiation is ray-traced in the Schwarzschild metric to a distant observer. We study the dependency with the source inclination of the pulse profile for different frequencies for these three models. The departure from a pure sinusoid of certain models at high inclination will be visible in the power density spectra by a higher presence of harmonics. In particular, hot spots and spirals lead to a (complete or partial) harmonic series which is lacking for a radially oscillating tori. We conclude that analyzing the first harmonics of the dominant power density spectrum peak for high-inclination sources is an interesting probe and it might make it possible to differentiate between axisymmetric (tori) and non-axisymmetric (hotspots and spirals) models.

  11. Numerical study of liquid-hydrogen droplet generation from a vibrating orifice

    NASA Astrophysics Data System (ADS)

    Xu, J.; Celik, D.; Hussaini, M. Y.; Van Sciver, S. W.

    2005-08-01

    Atomic hydrogen propellant feed systems for far-future spacecraft may utilize solid-hydrogen particle carriers for atomic species that undergo recombination to create hot rocket exhaust. Such technology will require the development of particle generation techniques. One such technique could involve the production of hydrogen droplets from a vibrating orifice that would then freeze in cryogenic helium vapor. Among other quantities, the shape and size of the droplet are of particular interest. The present paper addresses this problem within the framework of the incompressible Navier-Stokes equations for multiphase flows, in order to unravel the basic mechanisms of droplet formation with a view to control them. Surface tension, one of the most important mechanisms to determine droplet shape, is modeled as the source term in the momentum equation. Droplet shape is tracked using a volume-of-fluid approach. A dynamic meshing technique is employed to accommodate the vibration of the generator orifice. Numerically predicted droplet shapes show satisfactory agreement with photographs of droplets generated in experiments. A parametric study is carried out to understand the influence of injection velocity, nozzle vibrational frequency, and amplitude on the droplet shape and size. The computational model provides a definitive qualitative picture of the evolution of droplet shape as a function of the operating parameters. It is observed that, primarily, the orifice vibrational frequency affects the shape, the vibrational amplitude affects the time until droplet detachment from the orifice, and the injection velocity affects the size. However, it does not mean that, for example, there is no secondary effect of amplitude on shape or size.

  12. Modeling of High-Energy Pulsed Laser Interactions with Coupons

    SciTech Connect

    Boley, C D; Rubenchik, A M

    2003-02-06

    We describe a computational model of laser-materials interactions in the regime accessed by the solid state heat capacity lasers (SSHCLs) built at LLNL. We show that its predictions compare quite favorably with coupon experiments by the 10 kW SSHCL at LLNL. The body of this paper describes the following topics, listed by section number: (2) model in quiescent air, (3) comparison with experiments in quiescent air, (4) effects of air flow, (5) comparison with experiments involving air flow, (6) importance of material properties, (7) advantage of pulsed lasers over CW lasers, and (8) conclusions and recommendations.

  13. Model of pulse extraction from a copper laser amplifier

    SciTech Connect

    Boley, C.D.; Warner, B.E.

    1997-03-01

    A computational model of pulse propagation through a copper laser amplifier has been developed. The model contains a system of 1-D (in the axial direction), time-dependent equations for the laser intensity and amplified spontaneous emission (ASE), coupled to rate equations for the atomic levels. Detailed calculations are presented for a high-power amplifier at Lawrence Livermore National Laboratory. The extracted power agrees with experiment near saturation. At lower input power the calculation overestimates experiment, probably because of increased ASE effects. 6 refs., 6 figs.

  14. Static pressure orifice system testing method and apparatus

    NASA Technical Reports Server (NTRS)

    Culotta, R. F.; Posey, D. L. (Inventor)

    1980-01-01

    A method and apparatus are presented for pressure testing the static pressure orifices and associated connections used in wind tunnels. A cylindrical module, having in one end an open hemispherical calibration pressure chamber separated from and surrounded by an annular vacuum chamber is placed over the orifice of the system to be tested. O-rings ensure seating and a vacuum seal between the chambered end of the module and the surface around the orifice: one O-ring separates the outer chamber from the outside environment. Ports lead from each of the chambers out the other end of the module to tubes connected to a control box consisting of calibration pressure and vacuum supply lines, bleeder valves, and gauges.

  15. Effect of nonsymmetrical flow resistance upon orifice impedance resistance

    NASA Technical Reports Server (NTRS)

    Posey, J. W.; Compton, K. J.

    1974-01-01

    A nonreactive orifice in an infinite baffle is analyzed. The pressure difference delta across the orifice varies sinusoidally with amplitude 1.0 and average value -P. The orifice resistance, delta p is discontinuous at zero velocity and exhibits the constant values R sub + and R sub - for u 0 and u 0, respectively. The resultant velocity has power in all harmonics of the excitation frequency. A quasi-linear resistance is defined and found to be relatively insensitive to the presence or absence of a resonant backing cavity; however, it does vary from 1.33 R sub + to 0.67 R sub + for a resistance ratio R sub +/R sub - between 0.5 and 2.0.

  16. Discharging Through an Orifice Determines Steam-Water Enthalpy

    SciTech Connect

    James, Russell

    1987-01-20

    A wide range of steam-water mixtures was discharged to the atmosphere through a 10.7 mm diameter orifice which was sharp-edged with a minuscule throat pressure tapping. The ratio of throat pressure to up-stream pressure was found sensitive to dryness fraction over the whole range studied from 0.03 to 1.0. The technique (employing large orifices) has the potential of identifying the unknown enthalpy of geothermal wells discharging large flows. Contrariwise, a nozzle (rounded entry orifice) was found remarkably _insensitive_ over most of the dryness range and hence is useless for such determinations; however, it can be used to measure the flow-rate when enthalpy is known. 2 figs., 7 refs.

  17. Theoretical transport modeling of Ohmic cold pulse experiments

    NASA Astrophysics Data System (ADS)

    Kinsey, J. E.; Waltz, R. E.; St. John, H. E.

    1998-11-01

    The response of several theory-based transport models in Ohmically heated tokamak discharges to rapid edge cooling due to trace impurity injection is studied. Results are presented for the Institute for Fusion Studies—Princeton Plasma Physics Laboratory (IFS/PPPL), gyro-Landau-fluid (GLF23), Multi-mode (MM), and the Itoh-Itoh-Fukuyama (IIF) transport models with an emphasis on results from the Texas Experimental Tokamak (TEXT) [K. W. Gentle, Nucl. Technol./Fusion 1, 479 (1981)]. It is found that critical gradient models containing a strong ion and electron temperature ratio dependence can exhibit behavior that is qualitatively consistent with experimental observation while depending solely on local parameters. The IFS/PPPL model yields the strongest response and demonstrates both rapid radial pulse propagation and a noticeable increase in the central electron temperature following a cold edge temperature pulse (amplitude reversal). Furthermore, the amplitude reversal effect is predicted to diminish with increasing electron density and auxiliary heating in agreement with experimental data. An Ohmic pulse heating effect due to rearrangement of the current profile is shown to contribute to the rise in the core electron temperature in TEXT, but not in the Joint European Tokamak (JET) [A. Tanga and the JET Team, in Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 65] and the Tokamak Fusion Test Reactor (TFTR) [R. J. Hawryluk, V. Arunsalam, M. G. Bell et al., in Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 51]. While this phenomenon is not necessarily a unique signature of a critical gradient, there is sufficient evidence suggesting that the apparent plasma response to edge cooling may not require any underlying nonlocal mechanism and may be explained within the context of the intrinsic properties of electrostatic drift

  18. Extension of an exponential light-curve gamma-ray burst pulse model across energy bands

    NASA Astrophysics Data System (ADS)

    Nemiroff, Robert J.

    2012-01-01

    A simple mathematical model of gamma-ray burst(GRB) pulses in time, suggested by Norris et al., is extended across energy. For a class of isolated pulses, two fit parameters appear to be effectively independent of energy. Specifically, statistical fits indicate that pulse amplitude A and pulse width τ are energy dependent, while pulse start time and pulse shape are effectively energy independent. These results bolster the pulse start and pulse scale conjectures of Nemiroff and add a new pulse shape conjecture which states that a class of pulses all have the same shape. The simple resulting pulse counts model is P(t, E) =A(E) exp[ -t/τ(E) -τ(E)/t], where t is the time since the start of the pulse. This pulse model is found to be an acceptable statistical fit to many of the fluent separable Burst and Transient Source Experiment (BATSE) pulses listed by Norris et al. Even without theoretical interpretation, this cross-energy extension may be immediately useful for fitting prompt emission from GRB pulses across energy channels with a minimal number of free parameters.

  19. Traveling Pulses for a Two-Species Chemotaxis Model.

    PubMed

    Emako, Casimir; Gayrard, Charlène; Buguin, Axel; Neves de Almeida, Luís; Vauchelet, Nicolas

    2016-04-01

    Mathematical models have been widely used to describe the collective movement of bacteria by chemotaxis. In particular, bacterial concentration waves traveling in a narrow channel have been experimentally observed and can be precisely described thanks to a mathematical model at the macroscopic scale. Such model was derived in [1] using a kinetic model based on an accurate description of the mesoscopic run-and-tumble process. We extend this approach to study the behavior of the interaction between two populations of E. Coli. Separately, each population travels with its own speed in the channel. When put together, a synchronization of the speed of the traveling pulses can be observed. We show that this synchronization depends on the fraction of the fast population. Our approach is based on mathematical analysis of a macroscopic model of partial differential equations. Numerical simulations in comparison with experimental observations show qualitative agreement. PMID:27071058

  20. Traveling Pulses for a Two-Species Chemotaxis Model

    PubMed Central

    Emako, Casimir; Gayrard, Charlène; Buguin, Axel; Neves de Almeida, Luís; Vauchelet, Nicolas

    2016-01-01

    Mathematical models have been widely used to describe the collective movement of bacteria by chemotaxis. In particular, bacterial concentration waves traveling in a narrow channel have been experimentally observed and can be precisely described thanks to a mathematical model at the macroscopic scale. Such model was derived in [1] using a kinetic model based on an accurate description of the mesoscopic run-and-tumble process. We extend this approach to study the behavior of the interaction between two populations of E. Coli. Separately, each population travels with its own speed in the channel. When put together, a synchronization of the speed of the traveling pulses can be observed. We show that this synchronization depends on the fraction of the fast population. Our approach is based on mathematical analysis of a macroscopic model of partial differential equations. Numerical simulations in comparison with experimental observations show qualitative agreement. PMID:27071058

  1. Acoustic response of a rectangular levitator with orifices

    NASA Technical Reports Server (NTRS)

    El-Raheb, Michael; Wagner, Paul

    1990-01-01

    The acoustic response of a rectangular cavity to speaker-generated excitation through waveguides terminating at orifices in the cavity walls is analyzed. To find the effects of orifices, acoustic pressure is expressed by eigenfunctions satisfying Neumann boundary conditions as well as by those satisfying Dirichlet ones. Some of the excess unknowns can be eliminated by point constraints set over the boundary, by appeal to Lagrange undetermined multipliers. The resulting transfer matrix must be further reduced by partial condensation to the order of a matrix describing unmixed boundary conditions. If the cavity is subjected to an axial temperature dependence, the transfer matrix is determined numerically.

  2. Phenomenological Model of Current Sheet Canting in Pulsed Electromagnetic Accelerators

    NASA Technical Reports Server (NTRS)

    Markusic, Thomas; Choueiri, E. Y.

    2003-01-01

    The phenomenon of current sheet canting in pulsed electromagnetic accelerators is the departure of the plasma sheet (that carries the current) from a plane that is perpendicular to the electrodes to one that is skewed, or tipped. Review of pulsed electromagnetic accelerator literature reveals that current sheet canting is a ubiquitous phenomenon - occurring in all of the standard accelerator geometries. Developing an understanding of current sheet canting is important because it can detract from the propellant sweeping capabilities of current sheets and, hence, negatively impact the overall efficiency of pulsed electromagnetic accelerators. In the present study, it is postulated that depletion of plasma near the anode, which results from axial density gradient induced diamagnetic drift, occurs during the early stages of the discharge, creating a density gradient normal to the anode, with a characteristic length on the order of the ion skin depth. Rapid penetration of the magnetic field through this region ensues, due to the Hall effect, leading to a canted current front ahead of the initial current conduction channel. In this model, once the current sheet reaches appreciable speeds, entrainment of stationary propellant replenishes plasma in the anode region, inhibiting further Hall-convective transport of the magnetic field; however, the previously established tilted current sheet remains at a fairly constant canting angle for the remainder of the discharge cycle, exerting a transverse J x B force which drives plasma toward the cathode and accumulates it there. This proposed sequence of events has been incorporated into a phenomenological model. The model predicts that canting can be reduced by using low atomic mass propellants with high propellant loading number density; the model results are shown to give qualitative agreement with experimentally measured canting angle mass dependence trends.

  3. Effect of nozzle orifice geometry on spray, combustion, and emission characteristics under diesel engine conditions.

    SciTech Connect

    Som, S.; Longman, D. E; Ramirez, A. I.; Aggarwal, S. K.

    2011-03-01

    Diesel engine performance and emissions are strongly coupled with fuel atomization and spray processes, which in turn are strongly influenced by injector flow dynamics. Modern engines employ micro-orifices with different orifice designs. It is critical to characterize the effects of various designs on engine performance and emissions. In this study, a recently developed primary breakup model (KH-ACT), which accounts for the effects of cavitation and turbulence generated inside the injector nozzle is incorporated into a CFD software CONVERGE for comprehensive engine simulations. The effects of orifice geometry on inner nozzle flow, spray, and combustion processes are examined by coupling the injector flow and spray simulations. Results indicate that conicity and hydrogrinding reduce cavitation and turbulence inside the nozzle orifice, which slows down primary breakup, increasing spray penetration, and reducing dispersion. Consequently, with conical and hydroground nozzles, the vaporization rate and fuel air mixing are reduced, and ignition occurs further downstream. The flame lift-off lengths are the highest and lowest for the hydroground and conical nozzles, respectively. This can be related to the rate of fuel injection, which is higher for the hydroground nozzle, leading to richer mixtures and lower flame base speeds. A modified flame index is employed to resolve the flame structure, which indicates a dual combustion mode. For the conical nozzle, the relative role of rich premixed combustion is enhanced and that of diffusion combustion reduced compared to the other two nozzles. In contrast, for the hydroground nozzle, the role of rich premixed combustion is reduced and that of non-premixed combustion is enhanced. Consequently, the amount of soot produced is the highest for the conical nozzle, while the amount of NOx produced is the highest for the hydroground nozzle, indicating the classical tradeoff between them.

  4. A neuron model of stochastic resonance using rectangular pulse trains.

    PubMed

    Danziger, Zachary; Grill, Warren M

    2015-02-01

    Stochastic resonance (SR) is the enhanced representation of a weak input signal by the addition of an optimal level of broadband noise to a nonlinear (threshold) system. Since its discovery in the 1980s the domain of input signals shown to be applicable to SR has greatly expanded, from strictly periodic inputs to now nearly any aperiodic forcing function. The perturbations (noise) used to generate SR have also expanded, from white noise to now colored noise or vibrational forcing. This study demonstrates that a new class of perturbations can achieve SR, namely, series of stochastically generated biphasic pulse trains. Using these pulse trains as 'noise' we show that a Hodgkin Huxley model neuron exhibits SR behavior when detecting weak input signals. This result is of particular interest to neuroscience because nearly all artificial neural stimulation is implemented with square current or voltage pulses rather than broadband noise, and this new method may facilitate the translation of the performance gains achievable through SR to neural prosthetics. PMID:25186655

  5. Numerically Modeling Pulsed-Current, Kinked Wire Experiments

    NASA Astrophysics Data System (ADS)

    Filbey, Gordon; Kingman, Pat

    1999-06-01

    The U.S. Army Research Laboratory (ARL) has embarked on a program to provide far-term land fighting vehicles with electromagnetic armor protection. Part of this work seeks to establish robust simulations of magneto-solid-mechanics phenomena. Whether describing violent rupture of a fuse link resulting from a large current pulse or the complete disruption of a copper shaped-charge jet subjected to high current densities, the simulations must include effects of intense Lorentz body forces and rapid Ohmic heating. Material models are required that describe plasticity, flow and fracture, conductivity, and equation of state (EOS) parameters for media in solid, liquid, and vapor phases. An extended version of the Eulerian wave code CTH has been used to predict the apex motion of a V-shaped (``kinked'') copper wire 3mm in diameter during a 400 kilo-amp pulse. These predictions, utilizing available material, EOS, and conductivity data for copper and the known characteristics of an existing capacitor-bank pulsed power supply, were then used to configure an experiment. The experiments were in excellent agreement with the prior simulations. Both computational and experimental results (including electrical data and flash X-rays) will be presented.

  6. A Neuron Model of Stochastic Resonance Using Rectangular Pulse Trains

    PubMed Central

    Danziger, Zachary; Grill, Warren M

    2014-01-01

    Stochastic resonance (SR) is the enhanced representation of a weak input signal by the addition of an optimal level of broadband noise to a nonlinear (threshold) system. Since its discovery in the 1980s the domain of input signals shown to be applicable to SR has greatly expanded, from strictly periodic inputs to now nearly any aperiodic forcing function. The perturbations (noise) used to generate SR have also expanded, from white noise to now colored noise or vibrational forcing. This study demonstrates that a new class of perturbations can achieve SR, namely, series of stochastically generated biphasic pulse trains. Using these pulse trains as ‘noise’ we show that a Hodgkin Huxley model neuron exhibits SR behavior when detecting weak input signals. This result is of particular interest to neuroscience because nearly all artificial neural stimulation is implemented with square current or voltage pulses rather than broadband noise, and this new method may facilitate the translation of the performance gains achievable through SR to neural prosthetics. PMID:25186655

  7. 2-D Magnetohydrodynamic Modeling of A Pulsed Plasma Thruster

    NASA Technical Reports Server (NTRS)

    Thio, Y. C. Francis; Cassibry, J. T.; Wu, S. T.; Rodgers, Stephen L. (Technical Monitor)

    2002-01-01

    Experiments are being performed on the NASA Marshall Space Flight Center (MSFC) MK-1 pulsed plasma thruster. Data produced from the experiments provide an opportunity to further understand the plasma dynamics in these thrusters via detailed computational modeling. The detailed and accurate understanding of the plasma dynamics in these devices holds the key towards extending their capabilities in a number of applications, including their applications as high power (greater than 1 MW) thrusters, and their use for producing high-velocity, uniform plasma jets for experimental purposes. For this study, the 2-D MHD modeling code, MACH2, is used to provide detailed interpretation of the experimental data. At the same time, a 0-D physics model of the plasma initial phase is developed to guide our 2-D modeling studies.

  8. Experimental Investigation of Cavitation Induced Feedline Instability from an Orifice

    NASA Technical Reports Server (NTRS)

    Hitt, Matthew A.; Lineberry, David M.; Ahuja, Vineet; Frederick, Robert A,

    2012-01-01

    This paper details the results of an experimental investigation into the cavitation instabilities created by a circular orifice conducted at the University of Alabama in Huntsville Propulsion Research Center. This experiment was conducted in concert with a computational simulation to serve as a reference point for the simulation. Testing was conducted using liquid nitrogen as a cryogenic propellant simulant. A 1.06 cm diameter thin orifice with a rounded inlet was tested in an approximately 1.25 kg/s flow with inlet pressures ranging from 504.1 kPa to 829.3 kPa. Pressure fluctuations generated by the orifice were measured using a high frequency pressure sensor located 0.64 tube diameters downstream of the orifice. Fast Fourier Transforms were performed on the high frequency data to determine the instability frequency. Shedding resulted in a primary frequency with a cavitation related subharmonic frequency. For this experiment, the cavitation instability ranged from 153 Hz to 275 Hz. Additionally, the strength of the cavitation occur red as a function of cavitation number. At lower cavitation numbers, the strength of the cavitation instability ranged from 2.4 % to 7 % of the inlet pressure. However, at higher cavitation numbers, the strength of the cavitation instability ranged from 0.6 % to 1 % of the inlet pressure.

  9. 49 CFR 230.71 - Orifice testing of compressors.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 4 2013-10-01 2013-10-01 false Orifice testing of compressors. 230.71 Section 230.71 Transportation Other Regulations Relating to Transportation (Continued) FEDERAL RAILROAD ADMINISTRATION, DEPARTMENT OF TRANSPORTATION STEAM LOCOMOTIVE INSPECTION AND MAINTENANCE STANDARDS...

  10. 49 CFR 230.71 - Orifice testing of compressors.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 4 2014-10-01 2014-10-01 false Orifice testing of compressors. 230.71 Section 230.71 Transportation Other Regulations Relating to Transportation (Continued) FEDERAL RAILROAD ADMINISTRATION, DEPARTMENT OF TRANSPORTATION STEAM LOCOMOTIVE INSPECTION AND MAINTENANCE STANDARDS...

  11. 49 CFR 230.71 - Orifice testing of compressors.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 4 2010-10-01 2010-10-01 false Orifice testing of compressors. 230.71 Section 230.71 Transportation Other Regulations Relating to Transportation (Continued) FEDERAL RAILROAD ADMINISTRATION, DEPARTMENT OF TRANSPORTATION STEAM LOCOMOTIVE INSPECTION AND MAINTENANCE STANDARDS...

  12. Sound generation by steady flow through glottis-shaped orifices

    NASA Astrophysics Data System (ADS)

    Zhang, Zhaoyan; Mongeau, Luc; Frankel, Steven H.; Thomson, Scott; Park, Jong Beom

    2004-09-01

    Although the signature of human voice is mostly tonal, it also includes a significant broadband component. Quadrupolelike sources due to turbulence in the region downstream of the glottis, and dipolelike sources due to the force applied by the vocal folds onto the surrounding fluid are the two primary broadband sound generating mechanisms. In this study, experiments were conducted to characterize the broadband sound emissions of confined stationary jets through rubber orifices formed to imitate the approximate shape of the human glottis at different stages during one cycle of vocal fold vibrations. The radiated sound pressure spectra downstream of the orifices were measured for varying flow rates, orifice shapes, and gas mixtures. The nondimensional sound pressure spectra were decomposed into the product of three functions: a source function F, a radiation efficiency function M, and an acoustic response function G. The results show that, as for circular jets, the quadrupole source contributions dominated for straight and convergent orifices. For divergent jets, whistling tonal sounds were emitted at low flow rates. At high flow rates for the same geometry, dipole contributions dominated the sound radiated by free jets. However, possible source-load acoustic feedback may have hampered accurate source identification in confined flows.

  13. Sound generation by steady flow through glottis-shaped orifices.

    PubMed

    Zhang, Zhaoyan; Mongeau, Luc; Frankel, Steven H; Thomson, Scott; Park, Jong Beom

    2004-09-01

    Although the signature of human voice is mostly tonal, it also includes a significant broadband component. Quadrupolelike sources due to turbulence in the region downstream of the glottis, and dipolelike sources due to the force applied by the vocal folds onto the surrounding fluid are the two primary broadband sound generating mechanisms. In this study, experiments were conducted to characterize the broadband sound emissions of confined stationary jets through rubber orifices formed to imitate the approximate shape of the human glottis at different stages during one cycle of vocal fold vibrations. The radiated sound pressure spectra downstream of the orifices were measured for varying flow rates, orifice shapes, and gas mixtures. The nondimensional sound pressure spectra were decomposed into the product of three functions: a source function F, a radiation efficiency function M, and an acoustic response function G. The results show that, as for circular jets, the quadrupole source contributions dominated for straight and convergent orifices. For divergent jets, whistling tonal sounds were emitted at low flow rates. At high flow rates for the same geometry, dipole contributions dominated the sound radiated by free jets. However, possible source-load acoustic feedback may have hampered accurate source identification in confined flows. PMID:15478439

  14. In-flight investigation of shuttle tile pressure orifice installations

    NASA Astrophysics Data System (ADS)

    Moes, Timothy R.; Meyer, Robert R., Jr.

    1990-09-01

    To determine shuttle orbiter wing loads during ascent, wing load instrumentation was added to Columbia (OV-102). This instrumentation included strain gages and pressure orifices on the wing. The loads derived from wing pressure measurements taken during STS 61-C did not agree with those derived from strain gage measurements or with the loads predicted from the aerodynamic database. Anomalies in the surface immediately surrounding the pressure orifices in the thermal protection system (TPS) tiles were one possible cause of errors in the loads derived from wing pressure measurements. These surface anomalies were caused by a ceramic filler material which was installed around the pressure tubing. The filler material allowed slight movement of the TPS tile and pressure tube as the airframe flexed and bent under aerodynamic loads during ascent and descent. Postflight inspection revealed that this filler material had protruded from or receeded beneath the surface, causing the orifice to lose its flushness. Flight tests were conducted at NASA Ames Research Center Dryden Flight Research Facility to determine the effects of any anomaly in surface flushness of the orifice installation on the measured pressures at Mach numbers between 0.6 and 1.4. An F-104 aircraft with a flight test fixture mounted beneath the fuselage was used for these flights. Surface flushness anomalies typical of those on the orbiter after flight (STA 61-C) were tested. Also, cases with excessive protrusion and recession of the filler material were tested. This report shows that the anomalies in STS 61-C orifice installations adversely affected the pressure measurements. But the magnitude of the affect was not great enough to account for the discrepancies with the strain gage measurements and the aerodynamic predictions.

  15. In-flight investigation of shuttle tile pressure orifice installations

    NASA Technical Reports Server (NTRS)

    Moes, Timothy R.; Meyer, Robert R., Jr.

    1990-01-01

    To determine shuttle orbiter wing loads during ascent, wing load instrumentation was added to Columbia (OV-102). This instrumentation included strain gages and pressure orifices on the wing. The loads derived from wing pressure measurements taken during STS 61-C did not agree with those derived from strain gage measurements or with the loads predicted from the aerodynamic database. Anomalies in the surface immediately surrounding the pressure orifices in the thermal protection system (TPS) tiles were one possible cause of errors in the loads derived from wing pressure measurements. These surface anomalies were caused by a ceramic filler material which was installed around the pressure tubing. The filler material allowed slight movement of the TPS tile and pressure tube as the airframe flexed and bent under aerodynamic loads during ascent and descent. Postflight inspection revealed that this filler material had protruded from or receeded beneath the surface, causing the orifice to lose its flushness. Flight tests were conducted at NASA Ames Research Center Dryden Flight Research Facility to determine the effects of any anomaly in surface flushness of the orifice installation on the measured pressures at Mach numbers between 0.6 and 1.4. An F-104 aircraft with a flight test fixture mounted beneath the fuselage was used for these flights. Surface flushness anomalies typical of those on the orbiter after flight (STA 61-C) were tested. Also, cases with excessive protrusion and recession of the filler material were tested. This report shows that the anomalies in STS 61-C orifice installations adversely affected the pressure measurements. But the magnitude of the affect was not great enough to account for the discrepancies with the strain gage measurements and the aerodynamic predictions.

  16. Axisymmetric Numerical Modeling of Pulse Detonation Rocket Engines

    NASA Technical Reports Server (NTRS)

    Morris, Christopher I.

    2005-01-01

    Pulse detonation rocket engines (PDREs) have generated research interest in recent years as a chemical propulsion system potentially offering improved performance and reduced complexity compared to conventional rocket engines. The detonative mode of combustion employed by these devices offers a thermodynamic advantage over the constant-pressure deflagrative combustion mode used in conventional rocket engines and gas turbines. However, while this theoretical advantage has spurred considerable interest in building PDRE devices, the unsteady blowdown process intrinsic to the PDRE has made realistic estimates of the actual propulsive performance problematic. The recent review article by Kailasanath highlights some of the progress that has been made in comparing the available experimental measurements with analytical and numerical models. In recent work by the author, a quasi-one-dimensional, finite rate chemistry CFD model was utilized to study the gasdynamics and performance characteristics of PDREs over a range of blowdown pressure ratios from 1-1000. Models of this type are computationally inexpensive, and enable first-order parametric studies of the effect of several nozzle and extension geometries on PDRE performance over a wide range of conditions. However, the quasi-one-dimensional approach is limited in that it cannot properly capture the multidimensional blast wave and flow expansion downstream of the PDRE, nor can it resolve nozzle flow separation if present. Moreover, the previous work was limited to single-pulse calculations. In this paper, an axisymmetric finite rate chemistry model is described and utilized to study these issues in greater detail. Example Mach number contour plots showing the multidimensional blast wave and nozzle exhaust plume are shown. The performance results are compared with the quasi-one-dimensional results from the previous paper. Both Euler and Navier-Stokes solutions are calculated in order to determine the effect of viscous

  17. Modelling hot electron generation in short pulse target heating experiments

    NASA Astrophysics Data System (ADS)

    Sircombe, N. J.; Hughes, S. J.

    2013-11-01

    Target heating experiments planned for the Orion laser facility, and electron beam driven fast ignition schemes, rely on the interaction of a short pulse high intensity laser with dense material to generate a flux of energetic electrons. It is essential that the characteristics of this electron source are well known in order to inform transport models in radiation hydrodynamics codes and allow effective evaluation of experimental results and forward modelling of future campaigns. We present results obtained with the particle in cell (PIC) code EPOCH for realistic target and laser parameters, including first and second harmonic light. The hot electron distributions are characterised and their implications for onward transport and target heating are considered with the aid of the Monte-Carlo transport code THOR.

  18. Numerical Modeling of Pulse Detonation Rocket Engine Gasdynamics and Performance

    NASA Technical Reports Server (NTRS)

    2003-01-01

    This paper presents viewgraphs on the numerical modeling of pulse detonation rocket engines (PDRE), with an emphasis on the Gasdynamics and performance analysis of these engines. The topics include: 1) Performance Analysis of PDREs; 2) Simplified PDRE Cycle; 3) Comparison of PDRE and Steady-State Rocket Engines (SSRE) Performance; 4) Numerical Modeling of Quasi 1-D Rocket Flows; 5) Specific PDRE Geometries Studied; 6) Time-Accurate Thrust Calculations; 7) PDRE Performance (Geometries A B C and D); 8) PDRE Blowdown Gasdynamics (Geom. A B C and D); 9) PDRE Geometry Performance Comparison; 10) PDRE Blowdown Time (Geom. A B C and D); 11) Specific SSRE Geometry Studied; 12) Effect of F-R Chemistry on SSRE Performance; 13) PDRE/SSRE Performance Comparison; 14) PDRE Performance Study; 15) Grid Resolution Study; and 16) Effect of F-R Chemistry on SSRE Exit Species Mole Fractions.

  19. Modelling of pulsed and steady-state DEMO scenarios

    NASA Astrophysics Data System (ADS)

    Giruzzi, G.; Artaud, J. F.; Baruzzo, M.; Bolzonella, T.; Fable, E.; Garzotti, L.; Ivanova-Stanik, I.; Kemp, R.; King, D. B.; Schneider, M.; Stankiewicz, R.; Stępniewski, W.; Vincenzi, P.; Ward, D.; Zagórski, R.

    2015-07-01

    Scenario modelling for the demonstration fusion reactor (DEMO) has been carried out using a variety of simulation codes. Two DEMO concepts have been analysed: a pulsed tokamak, characterized by rather conventional physics and technology assumptions (DEMO1) and a steady-state tokamak, with moderately advanced physics and technology assumptions (DEMO2). Sensitivity to impurity concentrations, radiation, and heat transport models has been investigated. For DEMO2, the impact of current driven non-inductively by neutral beams has been studied by full Monte Carlo simulations of the fast ion distribution. The results obtained are a part of a more extensive research and development (R&D) effort carried out in the EU in order to develop a viable option for a DEMO reactor, to be adopted after ITER for fusion energy research.

  20. A stochastic model for DNA electrotransfer with finite pulses

    NASA Astrophysics Data System (ADS)

    Yu, Miao; Lin, Hao

    2011-11-01

    Gene electrotransfer is a non-viral method to introduce foreign DNA into cells using electric fields. The fundamental mechanism for DNA transfer is unknown and under debate. While previous research investigated the role of DNA-membrane interaction and endocytosis, we here explore electrophoresis as a possible mechanism to assist translocation. In this model, DNA strands are treated as long-chain polymers driven through pores on the cell membrane by applied electric fields. A stochastic model is constructed, and solved numerically to parametrically study the time process of DNA translocation. Numerical results indicate that there exists an optimal pulse length beyond which DNA delivery probability no longer increases. The optimal length correlates inversely with applied field strength, and increases nonlinearly with DNA length. The results show good agreement with data from both solid-state nano-pore and electroporation experiments, and suggest that electrophoresis may play a key role in electroporation-mediated gene delivery.

  1. Using Cox cluster processes to model latent pulse location patterns in hormone concentration data.

    PubMed

    Carlson, Nichole E; Grunwald, Gary K; Johnson, Timothy D

    2016-04-01

    Many hormones, including stress hormones, are intermittently secreted as pulses. The pulsatile location process, describing times when pulses occur, is a regulator of the entire stress system. Characterizing the pulse location process is particularly difficult because the pulse locations are latent; only hormone concentration at sampled times is observed. In addition, for stress hormones the process may change both over the day and relative to common external stimuli. This potentially results in clustering in pulse locations across subjects. Current approaches to characterizing the pulse location process do not capture subject-to-subject clustering in locations. Here we show how a Bayesian Cox cluster process may be adapted as a model of the pulse location process. We show that this novel model of pulse locations is capable of detecting circadian rhythms in pulse locations, clustering of pulse locations between subjects, and identifying exogenous controllers of pulse events. We integrate our pulse location process into a model of hormone concentration, the observed data. A spatial birth-and-death Markov chain Monte Carlo algorithm is used for estimation. We exhibit the strengths of this model on simulated data and adrenocorticotropic and cortisol data collected to study the stress axis in depressed and non-depressed women. PMID:26553914

  2. ARTICLES: Thermohydrodynamic models of the interaction of pulse-periodic radiation with matter

    NASA Astrophysics Data System (ADS)

    Arutyunyan, R. V.; Baranov, V. Yu; Bol'shov, Leonid A.; Malyuta, D. D.; Mezhevov, V. S.; Pis'mennyĭ, V. D.

    1987-02-01

    Experimental and theoretical investigations were made of the processes of drilling and deep melting of metals by pulsed and pulse-periodic laser radiation. Direct photography of the surface revealed molten metal splashing due to interaction with single CO2 laser pulses. A proposed thermohydrodynamic model was used to account for the experimental results and to calculate the optimal parameters of pulse-periodic radiation needed for deep melting. The melt splashing processes were simulated numerically.

  3. Laboratory modeling of pulsed regimes of electron cyclotron instabilities

    NASA Astrophysics Data System (ADS)

    Golubev, S. V.; Mansfeld, D. A.; Viktorov, M. E.; Izotov, I. V.; Vodopyanov, A. V.; Demekhov, A. G.; Shalashov, A. G.

    2012-04-01

    propagating in the rarefied plasma across the external magnetic field. We have been able to explain the generation mechanism of the sequences of pulsed precipitations at the nonlinear instability growth phase in terms of a cyclotron maser model in which the instability threshold is exceeded through a reduction in electromagnetic energy losses characteristic of the plasma decay. The conditions in the decaying plasma resemble those in auroral plasma cavities and similar systems, and in this case electromagnetic waves with quasi-perpendicular propagation direction are excited.

  4. Order of Orifices: Sequence of Condom Use and Ejaculation by Orifice during Anal Intercourse among Women, Implications for HIV Transmission

    PubMed Central

    Gorbach, Pamina M.; Pines, Heather; Javanbakht, Marjan; Weiss, Robert E.; Jeffries, Robin; Cranston, Ross D.; Fuchs, Edward J; Hezerah, Marjan; Brown, Stephen; Voskanian, Alen; Anton, Peter

    2014-01-01

    Background For women the order of penile insertion, condom use, and ejaculation by orifice during sexual events affects the probability of HIV transmission and design of HIV prevention methods. Methods From October 2006-June 2009, 431 women in Los Angeles and Baltimore in a rectal health study reported the sequence of penile insertion, condom use, and ejaculation by orifice location by computer assisted self-interview. Multinomial logistic regression identified predictors of condom use by orifice among women who reported vaginal intercourse (VI) during their last anal intercourse (AI) event. Results Of the 192 reporting on a last AI event, 96.3% (180/187) reported VI. Of these, 83.1% had VI before AI; 66.1% reported ejaculation during VI and 45.2% during AI. Only one third used a condom for both VI and AI, less than 10% for VI only or AI only; and half used no condoms. After adjusting for race, partner type, and substance use, compared to women who used condoms for both VI and AI at last AI, being older (units=5 years) (adjusted odds ratio [AOR]=0.76, 95% confidence interval [CI]: 0.60, 0.96), with serodiscordant partners (AOR=0.22, 95% CI: 0.08, 0.61) and HIV-positive with seroconcordant partners (AOR = 0.15; 95% CI: 0.04, 0.54) were inversely associated with non-condom use. Conclusions For most of the women in our study VI accompanied AI, with AI usually occurring after VI. This evidence for use of multiple orifices during the same sexual encounter and low use of condoms across orifices supports the need for a multi-compartment HIV prevention strategy. PMID:25356778

  5. Modeling pulsed-laser melting of embedded semiconductor nanoparticles

    SciTech Connect

    Sawyer, C.A.; Guzman, J.; Boswell-Koller, C.N.; Sherburne, M.P.; Mastandrea, J.P.; Bustillo, K.C.; Ager III, J.W.; Haller, E.E.; Chrzan, D.C.

    2011-05-18

    Pulsed-laser melting (PLM) is commonly used to achieve a fast quench rate in both thin films and nanoparticles. A model for the size evolution during PLM of nanoparticles confined in a transparent matrix, such as those created by ion-beam synthesis, is presented. A self-consistent mean-field rate equations approach that has been used successfully to model ion beam synthesis of germanium nanoparticles in silica is extended to include the PLM process. The PLM model includes classical optical absorption, multiscale heat transport by both analytical and finite difference methods, and melting kinetics for confined nanoparticles. The treatment of nucleation and coarsening behavior developed for the ion beam synthesis model is modified to allow for a non-uniform temperature gradient and for interacting liquid and solid particles with different properties. The model allows prediction of the particle size distribution after PLM under various laser fluences, starting from any particle size distribution including as-implanted or annealed simulated samples. A route for narrowing the size distribution of embedded nanoparticles is suggested, with simulated distribution widths as low as 15% of the average size.

  6. Hydrodynamical modeling of laser drilling with short and ultrashort pulses

    NASA Astrophysics Data System (ADS)

    Ruf, Andreas; Breitling, Detlef; Berger, Peter; Dausinger, Friedrich; Huegel, Helmut

    2003-11-01

    This contribution examines the basic concepts and results of two laser ablation models based on commercially available hydrodynamical codes. In both cases the different material phases are described continuously by a single numerical algorithm. The first approach uses a finite-element model for the simultaneous description of solid and melt. It is thereby particularly suited for the description of melt formation and ejection. The results indicate a slow acceleration of the melt during the laser pulse up to velocities of some 10m/s followed by a rather steady-going ejection which is finally cut off by the resolidification. Although it was possible to examine this expulsion process, the model showed considerable numerical stability problems for higher intensities and the ultrasonic vapor expansion cannot be included. To overcome these shortages another model is proposed which is based on an equation of state for the target material in combination with a special pressure-based solver. Besides the continuous description of the material states, it also includes a continuous treatment of the beam propagation and energy coupling by solving Maxwell's equations. Although the work on this model is still going on, some of its basic prospects and limitations can already be discussed.

  7. Vortex structures in turbulent channel flow behind an orifice

    NASA Astrophysics Data System (ADS)

    Makino, Soichiro; Iwamoto, Kaoru; Kawamura, Hiroshi

    2006-11-01

    Direct numerical simulation of a channel flow with an orifice has been performed for Reτ0=10 - 600, where uτ0 is the friction velocity calculated from the mean pressure gradient, δ the channel half width and ν the kinematic viscosity. In the wake region, the mean flow becomes asymmetric by the Coanda effect. The degree of asymmetry increases with increasing the Reynolds number for the laminar flow at Reτ0< 50. The degree decreases abruptly at Reτ0=50, where the transition from the laminar to the turbulent flow take places. Large-scale spanwise vortices generated at the orifice edges. They become deformed and break up into disordered small-scale structures in shear layer. The small-scale vortices are convected towards the channel center. The large-scale vortices have an important effect upon the reattachment locations and streamwise vortices near the wall in the wake region.

  8. Natural orifice transluminal endoscopic surgery (NOTES): implications for anesthesia.

    PubMed

    Schaefer, Michael

    2009-01-01

    Natural orifice transluminal endoscopic surgery (NOTES) has recently evolved as a novel approach for abdominal surgery with great potential to further improve the advantages of laparoscopy over laparotomy. The first patients undergoing NOTES cholecystectomy or appendectomy reported no or only minimal pain, required no narcotic analgesics, and were discharged early from the hospital and immediately resumed daily activities. If this is confirmed by randomized controlled clinical trials, what are the potential implications for anesthesia? PMID:20948698

  9. Inspection of Ureteral Orifices: The Pearl of Flexible Cystoscopy

    PubMed Central

    Matthews, Charmaine; Bushra, Hamid; Das, Sanjay; Pettersson, Bo

    2015-01-01

    Abstract Cystoscopy is most common diagnostic investigation. The examination technique and the findings, both normal and pathological, were well described described a hundred years ago. With technological advances, there has been over-emphasis on imaging modalities for diagnostic purposes. A basic maneuver of examining the ureteral orifices is sometimes rushed through when in fact careful examination can clinch the diagnosis. The importance is exemplified by two cases, one of which is a rare case of Xanthoma of the ureter.

  10. Standards for discharge measurement with standardized nozzles and orifices

    NASA Technical Reports Server (NTRS)

    1940-01-01

    The following standards give the standardized forms for two throttling devices, standard nozzles and standard orifices, and enable them to be used in circular pipes without calibration. The definition of the standards are applicable in principle to the calibration and use of nonstandardized throttling devices, such as the venturi tube. The standards are valid, likewise, as a basis for discharge measurements in the German acceptance standards.

  11. Experimental Visualization of Bubble Formation from an Orifice In Microgravity in the Presence of Electric Fields

    NASA Technical Reports Server (NTRS)

    Herman, C.; Iacona, E.; Foldes, I. B.; Suner, G.; Milburn, C.

    2002-01-01

    The formation of air bubbles injected into a stagnant, isothermal liquid in microgravity through an orifice was studied. The bubbles grew very large in microgravity. They attained a nearly spherical shape and showed pronounced affinity towards coalescence in the absence of electric fields and other perturbations. Under the influence of electric fields, periodic detachment was observed, with bubble sizes larger than in terrestrial conditions. The bubble shape was elongated. After detachment, the bubbles moved away from the electrode at which they formed without coalescing with other bubbles. Experimental data on bubble shape and size at detachment showed good agreement with models.

  12. Sonic injection through diamond orifices into a hypersonic flow

    NASA Astrophysics Data System (ADS)

    Fan, Huaiguo

    The objective for the present study was to experimentally characterize the performance of diamond shaped injectors for hypersonic flow applications. First, an extensive literature review was performed. Second, a small scale Mach 5.0 wind tunnel facility was installed. Third, a detailed experimental parametric investigation of sonic injection through a diamond orifice (five incidence angles and three momentum ratios) and a circular injector (three momentum ratios) into the Mach 5.0 freestream was performed. Also, the use of downstream plume vorticity control ramps was investigated. Fourth, a detailed analysis of the experimental data to characterize and model the flow for the present range of conditions was achieved. The experimental techniques include surface oil flow visualization, Mie-Scattering flow visualization, particle image velocimetry (PIV), shadowgraph photograph, and a five-hole mean flow probe. The results show that the diamond injectors have the potential to produce attached shock depending on the incidence angle and jet momentum ratio. For example, the incidence angles less than or equal to 45° at J = 0.43 generated attached interaction shocks. The attached shock produced reduced total pressure loss (drag for scramjet) and eliminated potential hot spots, associated with the upstream flow separation. The jet interaction shock angle increased with jet incidence angle and momentum ratio due to increased penetration and flow disturbances. The plume penetration and cross-sectional area increased with incidence angle and momentum ratio. The increased jet interaction shock angle and strength produced increased total pressure loss, jet interaction force and total normal force. The characteristic kidney bean shaped plume was not discernable from the diamond injectors indicating increased effectiveness for film cooling applications. A vorticity generation ramp increased the penetration of the plume and the plume shape was indicative of higher levels of

  13. Maximizing the rigidity of a large planar orifice air bearing.

    PubMed

    Mullen, Michael; Broadhurst, John

    2014-08-01

    A rotating support for a large astronomical mirror has been implemented using an opposed surface planar orifice air bearing. This bearing needs to provide rotation as free as possible of static and dynamic friction, as well as maximizing the resistance to sudden angular deviations produced by wind gusts. Information on the design of traditional bearings, namely, a cavity supplied with air under pressure through an orifice or diffuser flow restriction and closed by the moving member, has been published in detail. These traditional bearings are not suitable for the application described, due to their slow speed of response to transient changes in forces, a considerable volume of air being needed to change the pressure in the cavity. The air bearing used in this application has no cavity but consists of two flat surfaces in close proximity with air under pressure introduced at the center of one of the surfaces. The volume of air in the bearing is therefore minimized, improving the response to load change transients. The load capacity of this type bearing is reduced as the air between the bearing surfaces is not at constant pressure, but is expanding from the center point of injection to its escape at the edges. This paper indicates a quantitative method of determining the size of the air supply orifices to achieve the maximum rigidity orthogonal to the direction of motion. The approach described can also be applied to optimizing the geometry of other non-cavity air bearings. PMID:25173317

  14. Numerical Modeling of Pulse Detonation Rocket Engine Gasdynamics And Performance

    NASA Technical Reports Server (NTRS)

    Morris, Christopher I.

    2004-01-01

    Pulse detonation rocket engines (PDREs) offer potential performance improvements over conventional designs, but represent a challenging modeling task. A quasi-1-D, finite-rate chemistry computational fluid dynamics model for PDREs is described and implemented. Four different PDRE geometries are evaluated in this work: a baseline detonation tube, a detonation tube with a straight extension, and a detonation tube with two types of converging-diverging (C-D) nozzles. The effect of extension length and C-D nozzle area ratio on the single-shot gasdynamics and performance of a PDRE is studied over a wide range of blowdown pressure ratios (1-1000). The results indicate that a C-D nozzle is generally more effective than a straight extension in improving PDRE performance, particularly at higher pressure ratios. Additionally, the results show that the blowdown process of the C-D nozzle systems could be beneficially cut off well before the pressure at the end-wall reaches the ambient value. The performance results are also compared to a steady-state rocket system using similar modeling assumptions.

  15. High energy pulsed inductive thruster modeling operating with ammonia propellant

    SciTech Connect

    Mikellides, Pavlos G.; Villarreal, James K.

    2007-11-15

    Numerical modeling of the pulsed inductive thruster operating with ammonia propellant at high energy levels, utilized a time-dependent, two-dimensional, and axisymmetric magnetohydrodynamics code to provide bilateral validation of experiment and theory and offer performance insights for improved designs. The power circuit model was augmented by a plasma voltage algorithm that accounts for the propellant's time-dependent resistance and inductance to properly account for plasma dynamics and was verified using available analytic solutions of two idealized plasma problems. Comparisons of the predicted current waveforms to experimental data exhibited excellent agreement for the initial half-period, essentially capturing the dominant acceleration phase. Further validation proceeded by comparisons of the impulse for three different energy levels, 2592, 4050, and 4608 J and a wide range of propellant mass values. Predicted impulse captured both trends and magnitudes measured experimentally for nominal operation. Interpretation of the modeling results in conjunction to experimental observations further confirm the critical mass phenomenon beyond which efficiency degrades due to elevated internal energy mode deposition and anomalous operation.

  16. Observational Study On Thermal Flow And Condensation Of Injecting Steam From Various Submerged Orifices

    NASA Astrophysics Data System (ADS)

    Kamei, Shuya; Hirata, Masaru

    1983-03-01

    It has been recognized that the steam accumulator plays an important role as one of thermal energy storage system and was used at hospitals, hotels and food factories in recent years. Experiments have been carried out to investigate direct contact condensation of saturated steam into a quiescent subcooled water environment. They were performed for subcooling from 20 - 70°C, for atmospheric pressure, and for various type of orifice ( single-orifice, multi-orifice and porous-disc-orifice ). The phenomena were observed by means of high speed shadowgraphy using a rotating prism camera. The phenomena were also visualized by techniques of liquid crystal using a still camera. The effect of bulk temperature in a water tank and the difference among a single-orifice, a multi-orifice and porous-disc-orifice were discussed and good predictive results for the visualization of thermal flow in a quiescent subcooled water environment were obtained.

  17. Stimulated LIF studied using pulsed digital holography and modelling

    NASA Astrophysics Data System (ADS)

    Amer, Eynas; Stenvall, Jonas; Gren, Per; Sjödahl, Mikael

    2013-04-01

    A frequency tripled Q-switched Nd-YAG laser (wavelength 355 nm, pulse duration 12 ns) has been used to pump Coumarin 153 dye solved in ethanol. The laser induced fluorescence (LIF) spectrum has been recorded using a spectrometer at different dye concentrations. The frequency doubled 532 nm beam from the same laser is used as a probe beam to pass through the excited volume of the dye. Because of stimulated emission an increase of the probe (532 nm) beam energy is recorded and a reduction of the spontaneous fluorescence spectrum intensity is observed. A model was developed that approaches the trend of the gain as a function of the probe beam energy at low dye concentrations (less than 0.08 g/L). The stimulated LIF is further recorded using digital holography. Digital holograms were recorded for different dye concentrations using collimated laser light (532 nm) passed through the dye volume. Two holograms without and with the UV laser beam were recorded. Intensity maps were calculated from the recorded digital holograms and are used to calculate the gain of the green laser beam due to the stimulated fluorescence emission which is coupled to the dye concentration. The gain of the coherent 532 nm beam is seen in the intensity maps and its value is about 40% for a dye concentration of 0.32 g/L and decreases with the decrease of the dye concentration. The results show that pulsed digital holography can be coupled to the stimulated LIF effect for imaging fluorescent species.

  18. Magnetized plasma flow through a small orifice

    NASA Astrophysics Data System (ADS)

    Gunn, J. P.

    2001-03-01

    Deuterium plasma flow through a circular hole in a flat conducting plate is simulated by the two-dimensional object-oriented particle-in-cell code (XOOPIC) [J. P. Verboncoeur, A. B. Langdon, and N. T. Gladd, Comp. Phys. Comm. 87, 199 (1995)]. A constant magnetic field is oriented perpendicular to the plate surface, and parallel to the cylindrical axis of the hole. Charge neutralization on the interior surface of the hole leads to attenuation of the ion current throughput. The attenuation is stronger than would be expected from a finite Larmor radius model, due to acceleration of ions by the self-consistent radial electric field. The current attenuation has been measured by comparing two Langmuir probes that were operated simultaneously under a wide range of plasma conditions in Tore Supra [Equipe Tore Supra, IAEA-CN-64/02-2, International Atomic Energy Agency, Vienna, p. I-41 (1996)]. One probe was exposed directly to the plasma and the other was hidden behind a graphite shield pierced with either 3 or 4 mm diameter holes. Both the ion current attenuation and the floating potential drop are in reasonable agreement with the simulation results.

  19. Computational modeling of laser-plasma interactions: pulse self-modulation and energy transfer between intersecting laser pulses.

    PubMed

    Kupfer, Rotem; Barmashenko, Boris; Bar, Ilana

    2013-07-01

    The nonlinear interaction of intense femtosecond laser pulses with a self-induced plasma channel in air and the energy transfer between two intersecting laser pulses were simulated using the finite-difference time-domain particle-in-cell method. Implementation of a simple numerical code enabled modeling of various phenomena, including pulse self-modulation in the spatiotemporal and spectral domains, conical emission, and energy transfer between two intersecting laser beams. The mechanism for energy transfer was found to be related to a plasma waveguide array induced by Moiré patterns of the interfering electric fields. The simulation results provide a persuasive replication and explanation of previous experimental results, when carried out under comparable physical conditions, and lead to prediction of others. This approach allows us to further examine the effect of the laser and plasma parameters on the simulation results and to investigate the underlying physics. PMID:23944583

  20. Computational modeling of laser-plasma interactions: Pulse self-modulation and energy transfer between intersecting laser pulses

    NASA Astrophysics Data System (ADS)

    Kupfer, Rotem; Barmashenko, Boris; Bar, Ilana

    2013-07-01

    The nonlinear interaction of intense femtosecond laser pulses with a self-induced plasma channel in air and the energy transfer between two intersecting laser pulses were simulated using the finite-difference time-domain particle-in-cell method. Implementation of a simple numerical code enabled modeling of various phenomena, including pulse self-modulation in the spatiotemporal and spectral domains, conical emission, and energy transfer between two intersecting laser beams. The mechanism for energy transfer was found to be related to a plasma waveguide array induced by Moiré patterns of the interfering electric fields. The simulation results provide a persuasive replication and explanation of previous experimental results, when carried out under comparable physical conditions, and lead to prediction of others. This approach allows us to further examine the effect of the laser and plasma parameters on the simulation results and to investigate the underlying physics.

  1. Comparison of model fitting and gated integration for pulse shape discrimination and spectral estimation of digitized lanthanum halide scintillator pulses

    NASA Astrophysics Data System (ADS)

    McFee, J. E.; Mosquera, C. M.; Faust, A. A.

    2016-08-01

    An analysis of digitized pulse waveforms from experiments with LaBr3(Ce) and LaCl3(Ce) detectors is presented. Pulse waveforms from both scintillator types were captured in the presence of 22Na and 60Co sources and also background alone. Two methods to extract pulse shape discrimination (PSD) parameters and estimate energy spectra were compared. The first involved least squares fitting of the pulse waveforms to a physics-based model of one or two exponentially modified Gaussian functions. The second was the conventional gated integration method. The model fitting method produced better PSD than gated integration for LaCl3(Ce) and higher resolution energy spectra for both scintillator types. A disadvantage to the model fitting approach is that it is more computationally complex and about 5 times slower. LaBr3(Ce) waveforms had a single decay component and showed no ability for alpha/electron PSD. LaCl3(Ce) was observed to have short and long decay components and alpha/electron discrimination was observed.

  2. High Amplitude Acoustic Behavior of a Slit-Orifice Backed by a Cavity

    NASA Technical Reports Server (NTRS)

    Ahuja, K. K.; Gaeta, R. J., Jr.; DAgostino, M.

    2000-01-01

    The objective of this study was to acquire detailed acoustic data and limited flow visualization data for numerical validation of a new model of sound absorption by a very narrow rectangular slit backed by a cavity. The sound absorption model is that being developed by Dr. C. K. W. Tam of Florida State University. This report documents normal incidence impedance measurements of a singular rectangular slit orifice with no mean flow. All impedance measurements are made within a 1.12 inch (28.5 mm) diameter impedance tube using the two-microphone method for several frequencies in the range 1000 - 6000Hz and incident sound pressure levels in the range 130 - 150 dB. In the interest of leaving the analysis of the data to the developers of more advanced Analytical and computational models of sound absorption by narrow slits, we authors have refrained from giving our own explanations of the observed results, although many of the observed results can be explained using the classical understanding of sound absorption by orifices.

  3. High Amplitude Acoustic Behavior of a Slit-Orifice Backed by a Cavity

    NASA Technical Reports Server (NTRS)

    Ahuja, K. K.; Gaeta, R. J., Jr.; DAgostino, M.; Jones, Mike (Technical Monitor)

    2000-01-01

    The objective of the study reported here was to acquire detailed acoustic data and limited and flow visualization data for numerical validation a new model of sound absorption by a very narrow rectangular slit backed by a cavity. The sound absorption model is being developed by Dr. C. K. W. Tam of Florida State University. This report documents normal incidence impedance measurements of a singular rectangular slit orifice with no mean flow. All impedance measurements are made within a 1.12 inch (28.5 mm) diameter impedance tube using the two-microphone method for several frequencies in the range 1000-6000Hz and incident sound pressure levels in the range 130 - 150 dB. In the interest of leaving the analysis of the data to the developers of more advanced analytical and computational models of sound absorption by narrow slits, we have refrained from giving our own explanations of the observed results, although many of the observed results can be explained using the classical explanations of sound absorption by orifices.

  4. Modeling of High Efficiency Solar Cells Under Laser Pulse for Power Beaming Applications

    NASA Technical Reports Server (NTRS)

    Jain, Raj K.; Landis, Geoffrey A.

    1994-01-01

    Solar cells may be used as receivers for laser power beaming. To understand the behavior of solar cells when illuminated by a pulsed laser, the time response of gallium arsenide and silicon solar cells to pulsed monochromatic input has been modeled using a finite element solar cell model.

  5. Modeling and laser-based sensing of pulsed detonation engines

    NASA Astrophysics Data System (ADS)

    Barbour, Ethan A.

    This work is concerned with two major aspects of pulse detonation engines (PDE) research: modeling and laser-based sensing. The modeling addresses both ideal and real considerations relevant to PDE design. First, an ideal nozzle model is developed which provides a tool for choosing area ratios for fixed-geometry converging, diverging, or converging-diverging nozzles. Next, losses associated with finite-rate chemistry are investigated. It was found that PDEs can experience up to 10% reduction in specific impulse from this effect if 02 is used as the oxidizer, whereas the losses are negligible for air-breathing applications. Next, heat transfer and friction losses were investigated and found to be greater than the losses from simple straight-tube PDEs. These losses are most pronounced (˜15%) when converging nozzles are used. The second portion of this work focuses on laser-based absorption sensing for PDEs. The mid-infrared was chosen as the best way to address the challenges of signal-to-noise ratio, sensitivity, robustness, and sensor bandwidth. A water vapor sensor was developed and applied to the PDE at the Naval Postgraduate School. This sensor provided improvements in temperature accuracy, and it revealed that water (generated by the vitiator) inhibited performance of the engine. Next, a JP-10 absorption sensor was developed and applied to the same engine. This sensor provided thermometry data at a higher temporal resolution than the water sensor. The sensor also provided crucial information on equivalence ratio and fuel arrival time which enabled the engine to be successfully operated on JP-10 and air for the first time.

  6. Individualization of the parameters of the three-elements Windkessel model using carotid pulse signal

    NASA Astrophysics Data System (ADS)

    Żyliński, Marek; Niewiadomski, Wiktor; Strasz, Anna; GÄ siorowska, Anna; Berka, Martin; Młyńczak, Marcel; Cybulski, Gerard

    2015-09-01

    The haemodynamics of the arterial system can be described by the three-elements Windkessel model. As it is a lumped model, it does not account for pulse wave propagation phenomena: pulse wave velocity, reflection, and pulse pressure profile changes during propagation. The Modelflowmethod uses this model to calculate stroke volume and total peripheral resistance (TPR) from pulse pressure obtained from finger; the reliability of this method is questioned. The model parameters are: aortic input impedance (Zo), TPR, and arterial compliance (Cw). They were obtained from studies of human aorta preparation. Individual adjustment is performed based on the subject's age and gender. As Cw is also affected by diseases, this may lead to inaccuracies. Moreover, the Modelflowmethod transforms the pulse pressure recording from the finger (Finapres©) into a remarkably different pulse pressure in the aorta using a predetermined transfer function — another source of error. In the present study, we indicate a way to include in the Windkessel model information obtained by adding carotid pulse recording to the finger pressure measurement. This information allows individualization of the values of Cw and Zo. It also seems reasonable to utilize carotid pulse, which better reflects aortic pressure, to individualize the transfer function. Despite its simplicity, the Windkessel model describes essential phenomena in the arterial system remarkably well; therefore, it seems worthwhile to check whether individualization of its parameters would increase the reliability of results obtained with this model.

  7. Photon kinetic modeling of laser pulse propagation in underdense plasma

    SciTech Connect

    Reitsma, A. J. W.; Trines, R. M. G. M.; Bingham, R.; Cairns, R. A.; Mendonca, J. T.; Jaroszynski, D. A.

    2006-11-15

    This paper discusses photon kinetic theory, which is a description of the electromagnetic field in terms of classical particles in coordinate and wave number phase space. Photon kinetic theory is applied to the interaction of laser pulses with underdense plasma and the transfer of energy and momentum between the laser pulse and the plasma is described in photon kinetic terms. A comparison is made between a one-dimensional full wave and a photon kinetic code for the same laser and plasma parameters. This shows that the photon kinetic simulations accurately reproduce the pulse envelope evolution for photon frequencies down to the plasma frequency.

  8. Lattice Boltzmann investigation of acoustic damping mechanism and performance of an in-duct circular orifice.

    PubMed

    Ji, Chenzhen; Zhao, Dan

    2014-06-01

    In this work, three-dimensional numerical simulations of acoustically excited flow through a millimeter-size circular orifice are conducted to assess its noise damping performance, with particular emphasis on applying the lattice Boltzmann method (LBM) as an alternative computational aeroacoustics tool. The model is intended to solve the discrete lattice Boltzmann equation (LBE) by using the pseudo-particle based technique. The LBE controls the particles associated with collision and propagation over a discrete lattice mesh. Flow variables such as pressure, density, momentum, and internal energy are determined by performing a local integration of the particle distribution at each time step. This is different from the conventional numerical investigation attempting to solve Navier-Stokes (NS) equations by using high order finite-difference or finite-volume methods. Compared with the conventional NS solvers, one of the main advantages of LBM may be a reduced computational cost. Unlike frequency domain simulations, the present investigation is conducted in time domain, and the orifice damping behavior is quantified over a broad frequency range at a time by forcing an oscillating flow with multiple tones. Comparing the numerical results with those obtained from the theoretical models, large eddy simulation, and experimental measurements, good agreement is observed. PMID:24907789

  9. Performance evaluation of a developed orifice type heater for thermal compensation control at J-PARC cryogenic hydrogen system

    NASA Astrophysics Data System (ADS)

    Tatsumoto, H.; Aso, T.; Ohtsu, K.; Kawakami, Y.

    2015-12-01

    Supercritical hydrogen with a temperature of less than 20 K and a pressure of 1.5 MPa is used as moderator material at J-PARC. Total nuclear heating of 3.75 kW is generated by three moderators for a 1-MW proton beam operation. We have developed an orifice-type high-power heater for thermal compensation to mitigate hydrogen pressure fluctuation caused by the abrupt huge heat load and to reduce the fluctuation in the temperature of the supply hydrogen to less than 0.25 K. Through a performance test, we confirmed that the developed orifice-type heater could be heated uniformly and showed fast response, as expected. Furthermore, a simulation model that can describe heater behaviors has been established on the basis of the experimental data. The heater control approach was studied using the aforementioned heater simulation model and a dynamic simulation code developed by the authors.

  10. A physics-based model of the electric field pulses occurring during the lightning initiation

    NASA Astrophysics Data System (ADS)

    Kaspar, Petr; Santolik, Ondrej; Kolmasova, Ivana

    2016-04-01

    We investigate properties of the electric field pulses observed during the lightning initiation using a generalization of electrostatic and transmission-line models. In the model, the initial leader has a finite conductivity, the current in the channel is inducted owing to an ambient field generated by charge structure inside a thundercloud, and the electric field is computed by a formula derived from exact solution of the Maxwell's equations for a given inducted current. We show how the shape of electric field waveform of individual pulses depends on various parameters of the model with an emphasis on the thundercloud charge structure. We generalize the model to include sequences of several electric field pulses. We show how the peak current pulse is related to the preliminary breakdown electric field peak pulse and we compare this estimation with observations.

  11. Atresia of the right atrioventricular orifice with atrioventricular concordance.

    PubMed Central

    Dickinson, D F; Wilkinson, J L; Smith, A; Anderson, R H

    1979-01-01

    Three hearts are described in which a fibrous membrane was interposed between the right atrium and a formed but hypoplastic right ventricle, which possessed recognisable inlet, trabecular, and infundibular components. In these hearts the distribution of the conducting tissue was as expected for concordant atrioventricular connections, and contrasts with that seen in the classical type of 'tricuspid atresia'. The distinctive morphological and histological features of these specimens lend further support to our view that the majority of cases of atresia of the right atrioventricular orifice should be regarded as coming within the designation of 'the univentricular heart'. Images PMID:475940

  12. Characterization of surface position in a liquid dispensing orifice

    SciTech Connect

    Farahi, R H; Passian, Ali; Thundat, Thomas George; Lereu, Aude L; Tetard, Laurene; Jones, Yolanda

    2009-01-01

    Precision microdispencing technology delivers picoliter amounts of fluid for printing, electronic, optical, chemical and biomedical applications. In particular, microjetting is capable of accurate, flexible, and non-contact coating with polymers, thus allowing the functionalization of delicate microsensors such as microcantilevers. Information on various phases of droplet formation are important to control volume, uniformity, velocity and rate. One such aspect is the ringing of the meniscus after droplet breakoff which can affect subsequent drop formation. We present analysis of an optical characterization technique and experimental results on the behaviour of menisus oscillations in an orifice of a piezoelectric microjet.

  13. Modeling of an actively stabilized regenerative amplifier for OMEGA pulse-shaping applications

    NASA Astrophysics Data System (ADS)

    Skeldon, Mark D.; Babushkin, Andrei; Zuegel, Jonathan D.; Keck, Robert L.; Okishev, Andrey V.; Seka, Wolf D.

    1997-12-01

    We have modeled the output of a feedback stabilized regenerative amplifier (regen). We solve the rate equations including upper- and lower-laser-level lifetimes explicitly. The complete regen dynamics including the losses due to the feedback stabilizer are modeled. We provide a prescription for determining the injection-pulse shape required to produce a given output-pulse shape from this region. The model shows excellent agreement to measured regen output. This model of the regen along with our code RAINBOW, completely describes the temporal dynamics of the OMEGA laser system allowing OMEGA users to specify on-target pulse shapes in advance.

  14. Fabrication and characterization of micro-orifices for diesel fuel injectors.

    SciTech Connect

    Fenske, G.; Woodford, J.; Wang, J.; El-Hannouny, E.; Schaefer, R.; Hamady, F.; National Vehicle and Fuel Emissions Lab.

    2007-04-01

    Stringent emission standards are driving the development of diesel-fuel injection concepts to mitigate in-cylinder formation of particulates. While research has demonstrated significant reduction in particulate formation using micro-orifice technology, implementation requires development of industrial processes to fabricate micro-orifices with diameters as low as 50 gmm and with large length-to-diameter ratios. This paper reviews the different processes being pursued to fabricate micro-orifices and the advanced techniques applied to characterize the performance of micro-orifices. The latter include the use of phase-contrast x-ray imaging of electroless nickel-plated, micro-orifices and laser imaging of fuel sprays at elevated pressures. The experimental results demonstrate an industrially viable process to create small uniform orifices that improve spray formation for fuel injection.

  15. Flow of granular matter in a silo with multiple exit orifices: jamming to mixing.

    PubMed

    Kamath, Sandesh; Kunte, Amit; Doshi, Pankaj; Orpe, Ashish V

    2014-12-01

    We investigate the mixing characteristics of dry granular material while draining down a silo with multiple exit orifices. The mixing in the silo, which otherwise consists of noninteracting stagnant and flowing regions, is observed to improve significantly when the flow through specific orifices is stopped intermittently. This momentary stoppage of flow through the orifice is either controlled manually or is chosen by the system itself when the orifice width is small enough to cause spontaneous jamming and unjamming. We observe that the overall mixing behavior shows a systematic dependence on the frequency of closing and opening of specific orifices. In particular, the silo configuration employing random jamming and unjamming of any of the orifices shows early evidence of chaotic mixing. When operated in a multipass mode, the system exhibits a practical and efficient way of mixing particles. PMID:25615084

  16. The Effect of Suppression of Vortex Generator Jets with Asymmetric Orifices on Flow Separation

    NASA Astrophysics Data System (ADS)

    Hasegawa, Hiroaki; Hayashi, Naoki

    In vortex generator jets (VGJs), the beneficial effect of separation control is obtained only if the jets are pitched to the lower wall and skewed with respect to the freestream direction. In particular, in the case of VGJs with circular orifices, the jets are pitched at an angle of 45 deg or less to the wall to achieve effective suppression, due to the generation of strong dominant vortices. On the other hand, it was confirmed that the vortices for the VGJs with the rectangular orifices are stronger and appear to provide more effective momentum transfer across the wall boundary layer, in contrast to the vortices for the VGJs with circular orifices in the previous study. In the present study, the suppression effect is investigated for VGJs with T-shaped orifices combined into two rectangular orifices in the case of a large pitch angle (60 deg). The VGJs with T-shaped orifices were practically applied to the flow separation control of a two-dimensional diffuser, and the suppression effect for the T-shaped orifices was compared to that for the circular orifices. The behavior and the decay of longitudinal vortices in the downstream direction are also described. The T-shaped orifices produce a counter-rotating vortex pair that has different strengths between positive and negative vortices, and longitudinal vortices exist near the lower wall. Therefore, the VGJs with T-shaped orifices provide more effective momentum transfer to the boundary layer and make the separation control effective, in contrast to the VGJs with circular orifices. The formation and behavior of the counter-rotating vortex pair produced by the interaction of the jets and the freestream in the downstream direction were strongly affected by the jet orifice shape.

  17. Model for electron detachment from negative ions by ultrashort half-cycle electric-field pulses

    NASA Astrophysics Data System (ADS)

    Grozdanov, T. P.; Jaćimović, J.

    2009-01-01

    We study a model for electron detachment from negative ions by ultrashort unipolar electric pulses. The electron-atom interaction is described by the zero-range potential and the temporal dependence of the electric field is approximated by the Dirac δ functions. The case of a single pulse can be treated semianalytically and explicit expressions are obtained for momentum and energy distributions of detached electrons as well as for the total detachment probability. The determination of angular distribution involves numerical evaluation of a one-dimensional integral. The case of two alternating electric pulses requires numerical evaluation of more complicated integrals but leads to interesting effects caused by the quantum interference of the electronic wave packets produced during the interactions with the first and the second pulses. The differential and integral detachment probabilities are calculated and discussed for a variety of pulse strengths and time delays between the pulses.

  18. Quasi-One-Dimensional Modeling of Pulse Detonation Rocket Engines

    NASA Technical Reports Server (NTRS)

    Morris, Christopher I.

    2002-01-01

    Pulsed detonation rocket engines (PDREs) have generated considerable research interest in recent years as a chemical propulsion system potentially offering improved performance and reduced complexity compared to conventional rocket engines. The detonative mode of combustion employed by these devices offers a thermodynamic advantage over the constant-pressure deflagrative combustion mode used in conventional rocket engines and gas turbines. However, while this theoretical advantage has spurred a great deal of interest in building PDRE devices, the unsteady blowdown process intrinsic to the PDRE has made realistic estimates of the actual propulsive performance problematic. The recent review article by Kailasanath highlights some of the difficulties in comparing the available experimental measurements with numerical models. In a previous paper by the author, parametric studies of the performance of a single, straight-tube PDRE were reported. A 1-D, unsteady method of characteristics code, employing a constant-gamma assumption behind the detonation front, was developed for that study. Models of this type are computationally inexpensive, and are particularly useful for parametric performance comparisons. For example, a plot showing the specific impulse of various PDRE and steady-state rocket engine (SSRE) configurations as a function of blowdown pressure ratio. The performance curves clearly indicate that a straight-tube PDRE is superior in specific impulse to a SSRE with a sonic nozzle over the entire range of pressure ratios. Note, however, that a straight-tube PDRE in general does not compare favorably to a SSRE fitted with an optimized de Laval supersonic nozzle, particularly at the high pressure ratios typical for boost or in-space rocket applications. However, the calculations also show that if a dynamically optimized, supersonic de Laval nozzle could be could be fitted to a PDRE, then the specific impulse of the device would exceed that of a comparable SSRE

  19. LANL Efforts on Neutron Coincidence Modeling of INL Pulsed Neutron Data

    SciTech Connect

    Stewart, Scott; Thron, Jonathan L.; Swinhoe, Martyn T.; Geist, William H.; Charlton, William S.

    2012-06-25

    Overview of this presentation is: (1) pulsed histogram analysis, (2) creation of SPNS, (3) use of SPNS for modeling pulsed neutron data, (4) creation of MUDI, (5) calculated accidentals correction using GUAM + MUDI, (6) background subtraction analysis, and (7) current/figure work with MCNP.

  20. Adjustable steam producing flexible orifice independent of fluid pressure

    NASA Technical Reports Server (NTRS)

    Morrison, Andrew D. (Inventor)

    1992-01-01

    A self-adjusting choke for a fluids nozzle includes a membrane constructed of a single piece of flexible or elastic material. This flexible material is shaped to fit into the outlet of a nozzle. The body of the membrane has at least two flow channels, from one face to the other, which directs two streams of water to cross at the opening of the nozzle or at some point beyond. The elasticity and thickness of the membrane is selected to match the range of expected pressures and fluid velocities. The choke may have more than two flow channels, as long as they are aligned adjacent to one another and directed towards each other at the exit face. In a three orifice embodiment, one is directed upward, one is directed downward, and the one in the middle is directed forward. In this embodiment all three fluid streams intersect at some point past the nozzle opening. Under increased pressure the membrane will deform causing the orifices to realign in a more forward direction, causing the streams to intersect at a smaller angle. This reduces the force with which the separate streams impact each other, still allowing the separate streams to unify into a single stable spiralling stream in spite of the increased pressure.

  1. Laparoscopic natural orifice specimen extraction-colectomy: A systematic review

    PubMed Central

    Wolthuis, Albert M; de Buck van Overstraeten, Anthony; D’Hoore, André

    2014-01-01

    Over the last 20 years, laparoscopic colorectal surgery has shown equal efficacy for benign and malignant colorectal diseases when compared to open surgery. However, a laparoscopic approach reduces postoperative morbidity and shortens hospital stay. In the quest to optimize outcomes after laparoscopic colorectal surgery, reduction of access trauma could be a way to improve recovery. To date, one method to reduce access trauma is natural orifice specimen extraction (NOSE). NOSE aims to reduce access trauma in laparoscopic colorectal surgery. The specimen is delivered via a natural orifice and the anastomosis is created intracorporeally. Different methods are used to extract the specimen and to create a bowel anastomosis. Currently, specimens are delivered transcolonically, transrectally, transanally, or transvaginally. Each of these NOSE-procedures raises specific issues with regard to operative technique and application. The presumed benefits of NOSE-procedures are less pain, lower analgesia requirements, faster recovery, shorter hospital stay, better cosmetic results, and lower incisional hernia rates. Avoidance of extraction site laparotomy is the most important characteristic of NOSE. Concerns associated with the NOSE-technique include bacterial contamination of the peritoneal cavity, inflammatory response, and postoperative outcomes, including postoperative pain and the functional and oncologic outcomes. These issues need to be studied in prospective randomized controlled trials. The aim of this systematic review is to describe the role of NOSE in minimally invasive colorectal surgery. PMID:25278692

  2. On the performance and flow characteristics of jet pumps with multiple orifices.

    PubMed

    Oosterhuis, Joris P; Timmer, Michael A G; Bühler, Simon; van der Meer, Theo H; Wilcox, Douglas

    2016-05-01

    The design of compact thermoacoustic devices requires compact jet pump geometries, which can be realized by employing jet pumps with multiple orifices. The oscillatory flow through the orifice(s) of a jet pump generates asymmetric hydrodynamic end effects, which result in a time-averaged pressure drop that can counteract Gedeon streaming in traveling wave thermoacoustic devices. In this study, the performance of jet pumps having 1-16 orifices is characterized experimentally in terms of the time-averaged pressure drop and acoustic power dissipation. Upon increasing the number of orifices, a significant decay in the jet pump performance is observed. Further analysis shows a relation between this performance decay and the diameter of the individual holes. Possible causes of this phenomenon are discussed. Flow visualization is used to study the differences in vortex ring interaction from adjacent jet pump orifices. The mutual orifice spacing is varied and the corresponding jet pump performance is measured. The orifice spacing is shown to have less effect on the jet pump performance compared to increasing the number of orifices. PMID:27250166

  3. Flow through a cylindrical pipe with a periodic array of fractal orifices

    NASA Astrophysics Data System (ADS)

    van Melick, P. A. J.; Geurts, B. J.

    2013-12-01

    We apply direct numerical simulation (DNS) of the incompressible Navier-Stokes equations to predict flow through a cylindrical pipe in which a periodic array of orifice plates with a fractal perimeter is mounted. The flow is simulated using a volume penalization immersed boundary method with which the geometric complexity of the orifice plate is represented. Adding a periodic array of orifice plates to a cylindrical pipe is shown to increase the mixing efficiency of the flow in the laminar regime. The average stretching rate is shown to increase by a factor of up to 5, comparing pipe flow without orifice plates to flow passing through an orifice plate derived from the Koch snowflake fractal. The dispersion rate is shown to increase by a factor of up to 4. In laminar flow, the viscous forces are most important close to the walls, causing orifice geometries with the largest perimeter to exhibit the largest axial velocities near the centerline of the pipe and the largest pressure drop to maintain the prescribed volumetric flow rate. The immersed boundary method is also applied to turbulent flow through a ‘fractal-orifices pipe’ at Re = 4300. It is shown that the pressure drop that is required to maintain the specified volumetric flow rate decreases by about 15% on comparing orifice plates with a circular opening to orifice plates with more complex shapes that contain several corners such as triangles, squares, stars and the Koch snowflake.

  4. Dynamics model of the IBR-2M pulsed reactor for analysis of fast transition processes

    NASA Astrophysics Data System (ADS)

    Pepelyshev, Yu. N.; Popov, A. K.; Sumkhuu, D.; Sangaa, D.

    2015-05-01

    A nonlinear model of the IBR-2M pulsed reactor dynamics relating values of variables at discreet instants of time (when power pulses appear) is developed on the basis of the MATLAB program system. The tests of the model by simulating calculated processes in the IBR-2M reactor proved the correctness of the model. A tentative estimate of the transfer coefficient for the linear part of the automatic regulator is obtained.

  5. Finite Element Modeling of Pulsed Eddy Current Signals from Aluminum Plates Having Defects

    NASA Astrophysics Data System (ADS)

    Babbar, V. K.; Harlley, D.; Krause, T. W.

    2010-02-01

    The pulsed eddy current technique is being developed for detection of flaws located at depth within conducting structures. The present work investigates the pulsed eddy current response from flat-plate conductors having defects by using finite element modeling. Modeling revealed the optimum probe position with respect to a multilayer defect geometry. Models were also produced to investigate the effect of changing some probe parameters on pickup signal and penetration depth.

  6. Modeling the Pulse Signal by Wave-Shape Function and Analyzing by Synchrosqueezing Transform.

    PubMed

    Wu, Hau-Tieng; Wu, Han-Kuei; Wang, Chun-Li; Yang, Yueh-Lung; Wu, Wen-Hsiang; Tsai, Tung-Hu; Chang, Hen-Hong

    2016-01-01

    We apply the recently developed adaptive non-harmonic model based on the wave-shape function, as well as the time-frequency analysis tool called synchrosqueezing transform (SST) to model and analyze oscillatory physiological signals. To demonstrate how the model and algorithm work, we apply them to study the pulse wave signal. By extracting features called the spectral pulse signature, and based on functional regression, we characterize the hemodynamics from the radial pulse wave signals recorded by the sphygmomanometer. Analysis results suggest the potential of the proposed signal processing approach to extract health-related hemodynamics features. PMID:27304979

  7. Modeling the Pulse Signal by Wave-Shape Function and Analyzing by Synchrosqueezing Transform

    PubMed Central

    Wang, Chun-Li; Yang, Yueh-Lung; Wu, Wen-Hsiang; Tsai, Tung-Hu; Chang, Hen-Hong

    2016-01-01

    We apply the recently developed adaptive non-harmonic model based on the wave-shape function, as well as the time-frequency analysis tool called synchrosqueezing transform (SST) to model and analyze oscillatory physiological signals. To demonstrate how the model and algorithm work, we apply them to study the pulse wave signal. By extracting features called the spectral pulse signature, and based on functional regression, we characterize the hemodynamics from the radial pulse wave signals recorded by the sphygmomanometer. Analysis results suggest the potential of the proposed signal processing approach to extract health-related hemodynamics features. PMID:27304979

  8. Understanding variation in ecosystem pulse responses to wetting: Benefits of data-model coupling

    NASA Astrophysics Data System (ADS)

    Jenerette, D.

    2011-12-01

    Metabolic pulses of activity are a common ecological response to intermittently available resources and in water-limited ecosystems these pulses often occur in response to wetting. Net ecosystem CO2 exchange (NEE) in response to episodic wetting events is hypothesized to have a complex trajectory reflecting the distinct responses, or "pulses", of respiration and photosynthesis. To help direct research activities a physiological-based model of whole ecosystem metabolic activity up- and down-regulation was developed to investigate ecosystem energy balance and gas exchange pulse responses following precipitation events. This model was to investigate pulse dynamics from a local network of sites in southern Arizona, a global network of eddy-covariance ecosystem monitoring sites, laboratory incubation studies, and field manipulations. Pulse responses were found to be ubiquitous across ecosystem types. These pulses had a highly variable influence on NEE following wetting, ranging from large net sinks to sources of CO2 to the atmosphere. Much of the variability in pulse responses of NEE could be described through a coupled up- and down-regulation pulse response model. Respiration pulses were hypothesized to occur through a reduction in whole ecosystem activation energy; this model was both useful and corroborated through laboratory incubation studies of soil respiration. Using the Fluxnet eddy-covariance measurement database event specific responses were combined with the pulse model into an event specific twenty-five day net flux calculation. Across all events observed a general net accumulation of CO2 following a precipitation event, with the largest net uptake within deciduous broadleaf forests and smallest within grasslands. NEE pulses favored greater uptake when pre-event ecosystem respiration rates and total precipitation were higher. While the latter was expected, the former adds to previous theory by suggesting a larger net uptake of CO2 when pre-event metabolic

  9. Natural orifice transluminal endoscopic surgery: new minimally invasive surgery come of age.

    PubMed

    Huang, Chen; Huang, Ren-Xiang; Qiu, Zheng-Jun

    2011-10-21

    Although in the past two decades, laparoscopic surgery, considered as a great revolution in the minimally invasive surgery field, has undergone major development worldwide, another dramatic surgical revolution has quietly appeared in recent years. Ever since Kalloo's first report on transgastric peritoneoscopy in a porcine model in 2004, interest in a new surgical procedure named natural orifice transluminal endoscopic surgery (NOTES) has blossomed worldwide. Considering that a NOTES procedure could theoretically avoid any abdominal incision, operation-related pain and scarring, many surgeons and endoscopists have been enthusiastic in their study of this new technique. In recent years, several NOTES studies have been carried out on porcine models and even on humans, including transvaginal cholecystectomy, transgastric appendectomy, transvaginal appendectomy, and transvesical peritoneoscopy. So what is the current situation of NOTES and how many challenges do we still face? This review discusses the current research progress in NOTES. PMID:22110263

  10. Quarter-wave pulse tube

    NASA Astrophysics Data System (ADS)

    Swift, G. W.; Gardner, D. L.; Backhaus, S. N.

    2011-10-01

    In high-power pulse-tube refrigerators, the pulse tube itself can be very long without too much dissipation of acoustic power on its walls. The pressure amplitude, the volume-flow-rate amplitude, and the time phase between them evolve significantly along a pulse tube that is about a quarter-wavelength long. Proper choice of length and area makes the oscillations at the ambient end of the long pulse tube optimal for driving a second, smaller pulse-tube refrigerator, thereby utilizing the acoustic power that would typically have been dissipated in the first pulse-tube refrigerator's orifice. Experiments show that little heat is carried from the ambient heat exchanger to the cold heat exchanger in such a long pulse tube, even though the oscillations are turbulent and even when the tube is compactly coiled.

  11. Emergency transvaginal hybrid natural orifice transluminal endoscopic surgery.

    PubMed

    Noguera, J F; Cuadrado, A; Sánchez-Margallo, F M; Dolz, C; Asencio, J M; Olea, J M; Morales, R; Lozano, L; Vicens, J C

    2011-05-01

    In a clinical series, 10 consecutive female patients with intra-abdominal infections were successfully treated with natural orifice transluminal endoscopic surgery (NOTES) performed transvaginally. The surgery, which consisted of a hybrid NOTES procedure using a transvaginal approach, was performed on an emergency basis by the surgical team on call. The indications for surgery were acute cholecystitis (n = 6), acute appendicitis (n = 2), and pelvic peritonitis (n = 2) with intra-abdominal infection. The procedure was successfully performed in all patients using a dual-channel endoscope and mini-laparoscopy assistance. This is the first clinical series in which NOTES has been performed on an emergency basis to treat intra-abdominal infections. Transvaginal surgery for intra-abdominal infection is a feasible procedure for groups experienced in the elective NOTES approach. PMID:21165824

  12. Effects of Pulsed Electromagnetic Fields on Osteoporosis Model

    NASA Astrophysics Data System (ADS)

    Xiaowei, Yang; Liming, Wang; Guan, Z. C.; Yaou, Zhang; Xiangpeng, Wang

    The purpose of this paper was to investigate the preventive effects and long term effects of extremely low frequency pulsed electromagnetic fields (PEMFs), generated by circular coils and pulsed electromagnetic fields stimulators, on osteoporosis in bilaterally ovariectomized rats. In preventive experiment, thirty three-month old female Sprague-Dawley rats were randomly divided into three different groups: sham (SHAM), ovariectomy (OVX), PEMFs stimulation (PEMFs). All rats were subjected to bilaterally ovariectomy except those in SHAM group. The PEMFs group was exposed to pulsed electromagnetic fields with frequency 15 Hz, peak magnetic induction density 2.2mT and exposure time 2 hours per day. The bone mineral density (BMD) of vertebra and left femur were measured by dual energy X-ray absorptiometry at eighth week, twelfth week and sixteenth week after surgery. In long term effects experiment, forty four rats were randomly divided into sham (14 rats, SHAM), ovariectomy group (10 rats, OVX), 15Hz PEMFs group(10 rats, 15Hz) and 30Hz PEMFs group(10 rats, 30Hz) at twenty-sixth week after surgery. Rats in PEMFs groups were stimulated sixteen weeks. In preventive experiment, the Corrected BMD of vertebra and femur was significantly higher than that of OVX group after 16 weeks (P<0.001, P<0.001 respectively). In long term effects experiment, the vertebral BMD of 15Hz PEMFs group and 30Hz PEMFs group was significantly higher than that of OVX groups (P<0.01, P<0.05 respectively). The experimental results demonstrated that extremely low intensity, low frequency, single pulsed electromagnetic fields significantly slowed down the loss of corrected vertebral and femoral BMD in bilaterally ovariectomized rats and suggest that PEMFs may be beneficial in the treatment of osteoporosis.

  13. Normal position of the ureteral orifice in infancy and childhood: a quantitative study.

    PubMed

    Cussen, L J

    1979-05-01

    Normal values for the distance between the vesicoureteral orifice and the internal urethral orifice are given for different ages, heights, weights, crown-to-rump lengths and surface areas of infants and children. A simple estimate of approximate mean values for these measurements also is included. PMID:571481

  14. Identification of whistling ability of a single hole orifice from an incompressible flow simulation

    SciTech Connect

    Lacombe, Romain; Moussou, Pierre

    2012-07-01

    Pure tone noise from orifices in pipe result from vortex shedding with lock-in. Acoustic amplification at the orifice is coupled to resonant condition to create self-sustained oscillations. One key feature of this phenomenon is hence the ability of an orifice to amplify acoustic waves in a given range of frequencies. Here a numerical investigation of the linear response of an orifice is undertaken, with the support of experimental data for validation. The study deals with a sharp edge orifice. Its diameter equals to 0.015 m and its thickness to 0.005 m. The pipe diameter is 0.030 m. An air flow with a Mach number 0.026 and a Reynolds number 18000 in the main pipe is present. At such a low Mach number; the fluid behavior can reasonably be described as locally incompressible. The incompressible Unsteady Reynolds Averaged Navier-Stokes (URANS) equations are solved with the help of a finite volume fluid mechanics software. The orifice is submitted to an average flow velocity, with superimposed small harmonic perturbations. The harmonic response of the orifice is the difference between the upstream and downstream pressures, and a straightforward calculation brings out the acoustic impedance of the orifice. Comparison with experiments shows that the main physical features of the whistling phenomenon are reasonably reproduced. (authors)

  15. An Acoustic Demonstration Model for CW and Pulsed Spectrosocopy Experiments

    NASA Astrophysics Data System (ADS)

    Starck, Torben; Mäder, Heinrich; Trueman, Trevor; Jäger, Wolfgang

    2009-06-01

    High school and undergraduate students have often difficulties if new concepts are introduced in their physics or chemistry lectures. Lecture demonstrations and references to more familiar analogues can be of great help to the students in such situations. We have developed an experimental setup to demonstrate the principles of cw absorption and pulsed excitation - emission spectroscopies, using acoustical analogues. Our radiation source is a speaker and the detector is a microphone, both controlled by a computer sound card. The acoustical setup is housed in a plexiglas box, which serves as a resonator. It turns out that beer glasses are suitable samples; this also helps to keep the students interested! The instrument is controlled by a LabView program. In a cw experiment, the sound frequency is swept through a certain frequency range and the microphone response is recorded simultaneously as function of frequency. A background signal without sample is recorded, and background subtraction yields the beer glass spectrum. In a pulsed experiment, a short sound pulse is generated and the microphone is used to record the resulting emission signal of the beer glass. A Fourier transformation of the time domain signal gives then the spectrum. We will discuss the experimental setup and show videos of the experiments.

  16. Modeling of dielectric barrier discharge plasma actuators driven by repetitive nanosecond pulses

    SciTech Connect

    Likhanskii, Alexandre V.; Shneider, Mikhail N.; Macheret, Sergey O.; Miles, Richard B.

    2007-07-15

    A detailed physical model for an asymmetric dielectric barrier discharge (DBD) in air driven by repetitive nanosecond voltage pulses is developed. In particular, modeling of DBD with high voltage repetitive negative and positive nanosecond pulses combined with positive dc bias is carried out. Operation at high voltage is compared with operation at low voltage, highlighting the advantage of high voltages, however the effect of backward-directed breakdown in the case of negative pulses results in a decrease of the integral momentum transferred to the gas. The use of positive repetitive pulses with dc bias is demonstrated to be promising for DBD performance improvement. The effects of the voltage waveform not only on force magnitude, but also on the spatial profile of the force, are shown. The crucial role of background photoionization in numerical modeling of ionization waves (streamers) in DBD plasmas is demonstrated.

  17. Pulse timing during irreversible electroporation achieves enhanced destruction in a hindlimb model of cancer.

    PubMed

    Jiang, Chunlan; Shao, Qi; Bischof, John

    2015-04-01

    The use of irreversible electroporation (IRE) for cancer treatment has increased during the past decade due to many advantages over other focal therapies. However, despite early success in pre-clinical and clinical IRE trials, in vivo studies have shown that IRE suffers from an inability to destroy large volumes of cancer tissue without repeating treatment and/or increasing the applied electrical dose to dangerous levels. The present work demonstrates a simple method whereby treatment volumes can be enhanced by changing pulse timing (delivering pulsing in three trains, 30 s apart), without changing the electrical dose (51 pulses at pulse strengths of 600 V, durations of 50 µs, and repetition rates of 10 Hz), during IRE in a 3D hindlimb tumor model. Results show that 3 weeks of tumor growth delay was achieved with pulse timing compared to 1 week in baseline IRE (200% increase). Furthermore, the pulse timing approach does not introduce any foreign molecules into the body and can easily be integrated into existing treatment or enhancement protocols of IRE. The enhanced injury may correlate to longer pore exposures, or time during which pores exist on the membrane during pulse timing. This in turn increases the likelihood of membrane failure, and/or death from secondary injury such as loss of critical ions, proteins and other cellular components. In summary this work demonstrates a simple translational approach to increase 3D IRE treatment volumes in vivo by using pulse timing. PMID:25269611

  18. Study of the diameter and number of the pulmonary veins orifices.

    PubMed

    Niculescu, M C; Niculescu, V; Sişu, Alina Maria; Ciobanu, Iulia Camelia; Dăescu, Ecaterina; Petrescu, Codruţa Ileana; Jianu, Adelina; Rusu, M C

    2006-01-01

    The present study was made in the anatomy laboratory on 100 heart specimens. It was studied the morphological parameters about diameter and number of the atrial orifices of the pulmonary veins. The number of the orifices and their diameter depends on the lungs weight. Generally (70% of the cases) the orifices number is four and rarely three or five. An increased number of orifices are more frequently in the right side and a decreased number especially in the left side. The orifices diameter is much larger at the male's veins than the female's ones, and much larger in the right than the left side and also much larger at the superiors than the inferior veins. PMID:17106520

  19. Modelling the effects of pulse exposure of several PSII inhibitors on two algae.

    PubMed

    Copin, Pierre-Jean; Chèvre, Nathalie

    2015-10-01

    Subsequent to crop application and during precipitation events, herbicides can reach surface waters in pulses of high concentrations. These pulses can exceed the Annual Average Environmental Quality Standards (AA-EQS), defined in the EU Water Framework Directive, which aims to protect the aquatic environment. A model was developed in a previous study to evaluate the effects of pulse exposure for the herbicide isoproturon on the alga Scenedesmus vacuolatus. In this study, the model was extended to other substances acting as photosystem II inhibitors and to other algae. The measured and predicted effects were equivalent when pulse exposure of atrazine and diuron were tested on S. vacuolatus. The results were consistent for isoproturon on the alga Pseudokirchneriella subcapitata. The model is thus suitable for the effect prediction of phenylureas and triazines and for the algae used: S. vacuolatus and P. subcapitata. The toxicity classification obtained from the dose-response curves (diuron>atrazine>isoproturon) was conserved for the pulse exposure scenarios modelled for S. vacuolatus. Toxicity was identical for isoproturon on the two algae when the dose-response curves were compared and also for the pulse exposure scenarios. Modelling the effects of any pulse scenario of photosystem II inhibitors on algae is therefore feasible and only requires the determination of the dose-response curves of the substance and growth rate of unexposed algae. It is crucial to detect the longest pulses when measurements of herbicide concentrations are performed in streams because the model showed that they principally affect the cell density inhibition of algae. PMID:26011414

  20. Effects of brief pulse and ultrabrief pulse electroconvulsive stimulation on rodent brain and behaviour in the corticosterone model of depression.

    PubMed

    O'Donovan, Sinead; Dalton, Victoria; Harkin, Andrew; McLoughlin, Declan M

    2014-09-01

    Brief pulse electroconvulsive therapy (BP ECT; pulse width 0.5-1.5 ms) is the most effective treatment available for severe depression. However, its use is associated with side-effects. The stimulus in ultrabrief pulse ECT (UBP ECT; pulse width 0.25-0.3 ms) is more physiological and has been reported to be associated with less cognitive side-effects, but its antidepressant effectiveness is not yet well established. Using electroconvulsive stimulation (ECS), the animal model of ECT, we previously reported UBP ECS to be significantly less effective than well-established BP ECS in eliciting behavioural, molecular and cellular antidepressant-related effects in naïve rats. We have now compared the effects of BP and UBP ECS in an animal model of depression related to exogenous supplementation with the stress-induced glucocorticoid hormone, corticosterone. Corticosterone administration resulted in an increase in immobility time in the forced swim test (FST) (p < 0.01) and decreases in the expression of brain-derived neurotrophic factor (BDNF) (p < 0.05) and glial fibrillary acidic protein (GFAP) (p < 0.001) in the hippocampus and frontal cortex. There was no significant difference in the duration or type of seizure induced by BP (0.5 ms) or UBP (0.3 ms) ECS. UBP ECS proved to be as effective as BP ECS at inducing a behavioural antidepressant response in the FST with a significant decrease (p < 0.001) in immobility seen following administration of ECS. Both forms of ECS also induced significant increases in BDNF protein (p < 0.01) expression in the hippocampus. BP ECS (p < 0.05) but not UBP ECS induced a significant increase in GFAP levels in the hippocampus and frontal cortex. Overall, UBP ECS effectively induced antidepressant-related behavioural and molecular responses in the corticosterone supplementation model, providing the first preclinical data on the potential role of this form of ECS to treat a depression phenotype related to elevated corticosterone. PMID

  1. Computation of Transverse Injection Into Supersonic Crossflow With Various Injector Orifice Geometries

    NASA Technical Reports Server (NTRS)

    Foster, Lancert; Engblom, William A.

    2003-01-01

    Computational results are presented for the performance and flow behavior of various injector geometries employed in transverse injection into a non-reacting Mach 1.2 flow. 3-D Reynolds-Averaged Navier Stokes (RANS) results are obtained for the various injector geometries using the Wind code with the Mentor s Shear Stress Transport turbulence model in both single and multi-species modes. Computed results for the injector mixing, penetration, and induced wall forces are presented. In the case of rectangular injectors, those longer in the direction of the freestream flow are predicted to generate the most mixing and penetration of the injector flow into the primary stream. These injectors are also predicted to provide the largest discharge coefficients and induced wall forces. Minor performance differences are indicated among diamond, circle, and square orifices. Grid sensitivity study results are presented which indicate consistent qualitative trends in the injector performance comparisons with increasing grid fineness.

  2. Optimization of orifice geometry for cross-flow mixing in a cylindrical duct

    NASA Technical Reports Server (NTRS)

    Sowa, W. A.; Kroll, J. T.; Samuelsen, G. S.; Holdeman, J. D.

    1994-01-01

    Mixing of gaseous jets in a cross-flow has significant applications in engineering, one example of which is the dilution zone of a gas turbine combustor. Despite years of study, the design of jet injection in combustors is largely based on practical experience. A series of experiments was undertaken to delineate the optimal mixer orifice geometry. A cross-flow to core-flow momentum-flux ratio of 40 and a mass flow ratio of 2.5 were selected as representative of an advanced design. An experimental test matrix was designed around three variables: the number of orifices, the orifice aspect ratio (long-to-short dimension), and the orifice angle. A regression analysis was performed on the data to arrive at an interpolating equation that predicted the mixing performance of orifice geometry combinations within the range of the test matrix parameters. Results indicate that mixture uniformity is a non-linear function of the number of orifices, the orifice aspect ratio, and the orifice angle. Optimum mixing occurs when the asymptotic mean jet trajectories are in the range of 0.35 less than r/R less than 0.5 (where r = 0 is at the mixer wall) at z/R = 1.0. At the optimum number of orifices, the difference between shallow-angled slots with large aspect ratios and round holes is minimal and either approach will lead to good mixing performance. At the optimum number of orifices, it appears possible to have two local optimums where one corresponds to an aspect ratio of 1.0 and the other to a high aspect ratio.

  3. Collection efficiency and interstage loss of nanoparticles in micro-orifice-based cascade impactors

    NASA Astrophysics Data System (ADS)

    Liu, Chun-Nan; Awasthi, Amit; Hung, Yi-Hung; Tsai, Chuen-Jinn

    2013-04-01

    In this study, two micro-orifice-based cascade impactors, including the micro-orifice uniform deposit impactor (MOUDI, MSP Model 110) and the NCTU micro-orifice cascade impactor (NMCI), were tested for the collection efficiency and interstage loss of nanoparticles. In the NMCI, new nozzle plates with smooth nozzle shape made by the LIGA (Lithography, Electroplating, and Molding) process were used to replace the 7th-10th stages in one of the MOUDI. Test results show that after adjusting proper S/W ratios (S: jet to plate distance, W: nozzle diameter) to 2.52, 3.01, 13.44, and 24.75 for the 7th, 8th, 9th and 10th stage of the NMCI, respectively, and 5.56, 11.18, 9.3, and 10.9 for the 7th, 8th, 9th and 10th stage of the MOUDI, respectively, the cutoff aerodynamic diameters (dpa50) are close to the nominal values given in Marple et al. (1991). Different S/W ratios are needed due to differences in the nozzle shape and nozzle diameter between two cascade impactors. Total interstage loss of nanoparticles from the inlet to the 6th-10th stage of the MOUDI exists due to the convection-diffusion mechanism, which increases with decreasing dpa. For the MOUDI, total loss is 2.9-15.3 % (dpa: 105.8 to 15.4 nm) for the inlet to the 6th stage and it increases to 20.1-26.1 % (dpa: 23 to 15.4 nm) for the inlet to the 10th stage, respectively. Similar but slightly lower loss also exists in the NMCI. Field comparison tests in the ambient air show that mass size distributions measured by the MOUDI agree well with those of the NMCI. Finally, nozzle clogging tests using high concentration incense smokes indicate that the NMCI has a much less tendency for particles to clog in the nozzles than the MODUI.

  4. Pulse Tube Refrigerator

    NASA Astrophysics Data System (ADS)

    Matsubara, Yoichi

    The pulse tube refrigerator is one of the regenerative cycle refrigerators such as Stirling cycle or Gifford-McMahon cycle which gives the cooling temperature below 150 K down to liquid helium temperature. In 1963, W. E. Gifford invented a simple refrigeration cycle which is composed of compressor, regenerator and simple tube named as pulse tube which gives a similar function of the expander in Stirling or Gifford-McMahon cycle. The thermodynamically performance of this pulse tube refrigerator is inferior to that of other regenerative cycles. In 1984, however, Mikulin and coworkers made a significant advance in pulse tube configuration called as orifice pulse tube. After this, several modifications of the pulse tube hot end configuration have been developed. With those modifications, the thermodynamic performance of the pulse tube refrigerator became the same order to that of Stirling and Gifford-McMahon refrigerator. This article reviews the brief history of the pulse tube refrigerator development in the view point of its thermodynamically efficiency. Simplified theories of the energy flow in the pulse tube have also been described.

  5. Modeling of coherent beam combining from multimillijoule chirped pulse tapered fiber amplifiers

    NASA Astrophysics Data System (ADS)

    Andrianov, A. V.; Kim, A. V.; Anashkina, E. A.; Meyerov, I. B.; Lebedev, S. A.; Sergeev, A. M.; Koenig, K.; Mourou, G.

    2015-10-01

    The amplification of high energy chirped pulses in Large Mode Area tapered fiber amplifiers and their coherent combining have been investigated numerically. We have developed a three-dimensional model of strongly chirped nanosecond pulse amplification and compression back to femtosecond duration fully taking into account transverse and longitudinal variations of refractive index profile and distribution of active ions in the fiber, wavelength dependence of emission and absorption cross sections, gain saturation and Kerr nonlinearity. Modeling of Yb-doped fiber amplifier shows that up to 3 mJ of output energy can be extracted in 1 ns pulse with single-mode beam quality. Finally, we have investigated numerically the capabilities of compression and coherent combining of up to 36 perturbed amplifying channels in which high-order modes were excited and have obtained more than 70% combining efficiency and 380 fs compressed pulse duration.

  6. Finite Element Modeling of Pulsed Eddy Current Signals from Conducting Cylinders and Plates

    NASA Astrophysics Data System (ADS)

    Babbar, V. K.; Kooten, P. V.; Cadeau, T. J.; Krause, T. W.

    2009-03-01

    Pulsed eddy current technique is being developed for detection of flaws located at depth within conducting structures. The present work investigates the pulsed eddy current response from cylindrical and flat-plate conductors by using finite element modeling employing COMSOL Multiphysics commercial package. The benchmark case of a driver/pick-up coil configuration encircling a solid conducting cylinder is used to model the transient electromagnetic response of cylinders of different diameters and lengths. A good comparison with experimental results validates the model. The work was extended to model a planar coil response to flat-plate aluminum structures.

  7. A review of pulse tube refrigeration

    NASA Technical Reports Server (NTRS)

    Radebaugh, Ray

    1990-01-01

    This paper reviews the development of the three types of pulse tube refrigerators: basic, resonant, and orifice types. The principles of operation are given. It is shown that the pulse tube refrigerator is a variation of the Stirling-cycle refrigerator, where the moving displacer is substituted by a heat transfer mechanism or by an orifice to bring about the proper phase shifts between pressure and mass flow rate. A harmonic analysis with phasors is described which gives reasonable results for the refrigeration power, yet is simple enough to make clear the processes which give rise to the refrigeration. The efficiency and refrigeration power are compared with those of other refrigeration cycles. A brief review is given of the research being done at various laboratories on both one- and two-stage pulse tubes. A preliminary assessment of the role of pulse tube refrigerators is discussed.

  8. An integrated model describing the toxic responses of Daphnia magna to pulsed exposures of three metals.

    PubMed

    Hoang, Tham C; Tomasso, Joseph R; Klaine, Stephen J

    2007-01-01

    Some toxicology research in which toxicant exposures are continual (pulsed) rather than continuous have been reported. A number of toxicity models have been developed for pulsed and continuous exposures. Most of these models were developed based on one- or two-compartment, first-order toxicokinetics and were calibrated with organic compounds. In the present study, the relationship between mortality (after 21 d) of Daphnia magna in response to pulsed and continuous exposures to Cu, Zn, and Se was used to develop a model that integrated the effects of single and multiple pulsed metal exposures based on first-order uptake and depuration kinetics. Mortality was a function of exposure concentration, duration, and recovery time between exposures. The model was successfully validated using an independent data set. It is applicable to risk assessment and, potentially, may be incorporated with other models (e.g., the biotic ligand model) to predict the toxicity of pulsed metal exposures under a range of environmental conditions. PMID:17269470

  9. Semi-empirical analysis of liquid fuel distribution downstream of a plain orifice injector under cross-stream air flow

    NASA Astrophysics Data System (ADS)

    Chin, J. S.; Jiang, H. K.; Cao, M. H.

    1981-07-01

    A simple, flat-fan spray model is proposed, which can with two empirical parameters predict both the value and the position of liquid fuel distribution curve maximums downstream of a plain orifice injector under high-velocity cross flow. It was found that the model is useful in the preliminary design of the fan air flow portion of a turbofan afterburner, due to its ability to predict the influence on liquid fuel distribution of (1) such flow parameters as air velocity and viscosity, pressure and temperature; (2) injector parameters such as diameter and injection velocity; and (3) liquid properties including viscosity, density, and surface tension.

  10. Choked-Flow Inlet Orifice Bubbler for Creating Small Bubbles in Mercury

    SciTech Connect

    Wendel, Mark W; Abdou, Ashraf A; Riemer, Bernie

    2013-01-01

    Pressure waves created in liquid mercury pulsed spallation targets like the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory, induce cavitation damage on the target container. The cavitation damage is thought to limit the lifetime of the target for power levels at and above 1 MW. One way to mitigate the damage would be to absorb the pressure pulse energy into a dispersed population of small bubbles, however, creating a bubble size distribution that is sufficiently large and disperse in mercury is challenging due to the high surface tension. Also, measuring the population is complicated by the opacity and the high level of turbulent mixing. Recent advances in bubble diagnostics by batch sampling the mercury made it possible to compare bubble populations for different techniques in a SNS-1/20th scale test loop. More than 10 bubblers were tested and the most productive bubblers were taken for in-beam testing at the Los Alamos Neutron Science Center (LANSCE) WNR user facility. One bubbler design, referred to as the inlet-orifice bubbler, that showed moderate success in creating populations also has an added advantage that it could easily be included in the existing SNS full-scale mercury target configuration. Improvements to the bubbler were planned including a reduction of the nozzle size to choke the gas injection, thus steadying the injected mass flow and allowing multiple nozzles to work off of a common plenum. For the first time, reliable bubble population data are available in the prototypical target geometry and can be compared with populations that mitigated cavitation damage. This paper presents those experimental results.

  11. AxBAxB… pulsed atomic layer deposition: Numerical growth model and experiments

    NASA Astrophysics Data System (ADS)

    Muneshwar, Triratna; Cadien, Ken

    2016-02-01

    Atomic layer deposition (ALD) is widely used for the fabrication of advanced semiconductor devices and related nanoscale structures. During ALD, large precursor doses (>1000 L per pulse) are often required to achieve surface saturation, of which only a small fraction is utilized in film growth while the rest is pumped from the system. Since the metal precursor constitutes a significant cost of ALD, strategies to enhance precursor utilization are essential for the scaling of ALD processes. In the precursor reaction step, precursor physisorption is restricted by steric hindrance (mA1) from ligands on the precursor molecules. On reaction, some of these ligands are removed as by-products resulting in chemisorbed species with reduced steric hindrance (mA1 → mA2, where mA2 < mA1) and some of the initially hindered surface reaction sites becoming accessible for further precursor physisorption. To utilize these additional reaction sites, we propose a generalized AxBAxB… pulsed deposition where the total precursor dose (ΦA) is introduced as multiple x (x > 1, x ∈ I) short-pulses rather than a single pulse. A numerical first-order surface reaction kinetics growth model is presented and applied to study the effect of AxBAxB… pulsed ALD on the growth per cycle (GPC). The model calculations predict higher GPC for AxBAxB… pulsing than with ABAB… deposition. In agreement with the model predictions, with AxBAxB… pulsed deposition, the GPC was found to increase by ˜46% for ZrN plasma enhanced ALD (PEALD), ˜49% for HfO2 PEALD, and ˜8% for thermal Al2O3 ALD with respect to conventional ABAB… pulsed growth.

  12. Evaluation of pulsed high intensity focused ultrasound exposures on metastasis in a murine model.

    PubMed

    Hancock, Hilary; Dreher, Matthew R; Crawford, Nigel; Pollock, Claire B; Shih, Jennifer; Wood, Bradford J; Hunter, Kent; Frenkel, Victor

    2009-01-01

    High intensity focused ultrasound (HIFU) may be employed in two ways: continuous exposures for thermal ablation of tissue (> 60 degrees C), and pulsed-exposures for non-ablative effects, including low temperature hyperthermia (37-45 degrees C), and non thermal effects (e.g. acoustic cavitation and radiation forces). Pulsed-HIFU effects may enhance the tissue's permeability for improved delivery of drugs and genes, for example, by opening up gaps between cells in the vasculature and parenchyma. Inducing these effects may improve local targeting of therapeutic agents, however; concerns exist that pulsed exposures could theoretically also facilitate dissemination of tumor cells and exacerbate metastases. In the present study, the influence of pulsed-HIFU exposures on increasing metastatic burden was evaluated in a murine model with metastatic breast cancer. A preliminary study was carried out to validate the model and determine optimal timing for treatment and growth of lung metastases. Next, the effect of pulsed-HIFU on the metastatic burden was evaluated using quantitative image processing of whole-lung histological sections. Compared to untreated controls (2/15), a greater number of mice treated with pulsed-HIFU were found to have lungs "overgrown" with metastases (7/15), where individual metastases grew together such that they could not accurately be counted. Furthermore, area fraction of lung metastases (area of metastases/area of lungs) was approximately 30% greater in mice treated with pulsed-HIFU; however, these differences were not statistically significant. The present study details the development of an animal model for investigating the influence of interventional techniques or exposures (such as pulsed HIFU) on metastatic burden. PMID:19517258

  13. Synthetic Jets in Cross-flow. Part 2; Jets From Orifices of Different Geometry

    NASA Technical Reports Server (NTRS)

    Milanovic, Ivana M.; Zaman, K. B. M. Q.

    2003-01-01

    The flow fields of synthetic jets in a cross-flow from orifices of different geometry are investigated. The geometries include a straight, a tapered, a pitched and a cluster of nine orifices, all having the same cross-sectional area through which the perturbation is discharged into the cross-flow. The strength of the jet from the tapered orifice in comparison to that from the straight one is found to be only slightly enhanced. The flow field from the cluster of orifices, when viewed a few equivalent diameters downstream, is similar to that from the single orifice. However, the penetration is somewhat lower in the former case due to the increased mixing of the distributed jets with the cross-flow. The penetration for the pitched configuration is the lowest, as expected. The jet trajectories for the straight and pitched orifices are well represented by correlation equations available for steady jets-in-cross-flow. Distributions of streamwise velocity, vorticity as well as turbulence intensity are documented for various cases. In addition, distributions of phase-averaged velocity and vorticity for the cylindrical and the clustered orifices are presented providing an insight into the flow dynamics.

  14. Three-dimensional laser anemometer study of compressible flow through orifice plates

    NASA Astrophysics Data System (ADS)

    Morrison, Gerald L.

    1988-09-01

    Two experimental facilities were constructed, one for the measurement of the pressure distributions on the pipe wall upstream and downstream of the orifice plate and on the orifice plate surface and the other for use with a laser Doppler anemometer (LDA) system to measure the complex flow field inside the orifice run. Pressure measurements for Beta = 0.25, 0.50 and 0.75 were performed for a range of Reynolds numbers from 17,700 to 120,000. A five hole Pitot probe and a 3-D laser Doppler anemometer (LDA) were used to measure profiles of the axial and radial velocities downstream of the orifice plate. Both devices showed a large recirculation zone extending approximately 2.5 pipe diameters downstream. The 3-D LDA measurements clearly showed the vena contracta and a secondary recirculation zone near the downstream base of the orifice plate. The 3-D LDA also measured the entire Reynolds stress tensor distribution downstream of a Beta = 0.05 orifice for a Reynolds number of 17,700. Creare, Inc.'s Fluent program was used to predict the flow field inside a Beta = 0.50 orifice flow meter. Using assumed inlet conditions, the agreement between experimental and computed results was good.

  15. Determination of modeling parameters for power IGBTs under pulsed power conditions

    SciTech Connect

    Dale, Gregory E; Van Gordon, Jim A; Kovaleski, Scott D

    2010-01-01

    While the power insulated gate bipolar transistor (IGRT) is used in many applications, it is not well characterized under pulsed power conditions. This makes the IGBT difficult to model for solid state pulsed power applications. The Oziemkiewicz implementation of the Hefner model is utilized to simulate IGBTs in some circuit simulation software packages. However, the seventeen parameters necessary for the Oziemkiewicz implementation must be known for the conditions under which the device will be operating. Using both experimental and simulated data with a least squares curve fitting technique, the parameters necessary to model a given IGBT can be determined. This paper presents two sets of these seventeen parameters that correspond to two different models of power IGBTs. Specifically, these parameters correspond to voltages up to 3.5 kV, currents up to 750 A, and pulse widths up to 10 {micro}s. Additionally, comparisons of the experimental and simulated data will be presented.

  16. Model calibration for pressure drop in a pulse-jet cleaned fabric filter

    NASA Astrophysics Data System (ADS)

    Koehler, John L.; David, Leith

    A model based on Darcy's law allows prediction of pressure drop in a pulse-jet cleaned fabric filter. The model considers the effects of filtration velocity, dust areal density added during one filtration cycle, and pulse pressure. Data used to calibrate the model were collected in experiments with three fabric surface treatments and three dusts conducted at three filtration velocities, for a total of 27 different experimental conditions. The fabric used was polyester felt with untreated, singed, or PTFE-laminated surface. The dusts used were granite, limestone and fly ash. Filtration velocities were 50,75 and 100 mm s -1. Dust areal density added during one filtration cycle was constant, as was pulse pressure. Under these conditions, fabric surface treatment alone largely determined the values for two of the three constants in the model; the third constant depends on pressure drop characteristics of the venturi at the top of each filter bag.

  17. Computational modeling of on-demand solder delivery for fluxless MCM packaging applications

    SciTech Connect

    Essien, M.; Sackinger, P.A.; Peebles, H.C.

    1996-10-01

    The development of smaller circuit volumes in microelectronic applications, particularly Multichip Module (MCM) technology, entails deposition of minute quantities of solder, with volumes on the order of nanoliters. We propose a system for fluxless solder deposition which uses on-demand solder jetting for deposition of 200 micrometer diameter solder droplets onto aluminum pads. This work details the computational modeling performed to provide design parameters for a magneto-hydrodynamic solder jetter (MHD). A dimensionless analysis was used to relate the fluid properties, the orifice length and width, and the droplet size to the amplitude and duration of the pressure pulse. These results were used as the initial inputs for the fluid dynamics model, and subsequent iterations were performed to determine the operational parameters that lead to the formation of stable, single droplets. Results show that a maximum pulse amplitude on the order of 0.5 Mdynes/cm[sup 2] is necessary to dispense molten solder from a 200 micrometer diameter orifice. The size of the droplet was found to vary linearly with the applied pressure pulse. The duration of the pulse ranged from approximately 0.6 to 0.9 milliseconds. A theoretical description of the relationship between the orifice diameter, surface tension, and `Pinch-off` time is given, and is in agreement with the results of the computational model.

  18. Modeling crater formation in femtosecond-pulse laser damage from basic principles.

    PubMed

    Mitchell, Robert A; Schumacher, Douglass W; Chowdhury, Enam A

    2015-05-15

    We present the first fundamental simulation method for the determination of crater morphology due to femtosecond-pulse laser damage. To this end we have adapted the particle-in-cell (PIC) method commonly used in plasma physics for use in the study of laser damage and developed the first implementation of a pair potential for PIC codes. We find that the PIC method is a complementary approach to modeling laser damage, bridging the gap between fully ab-initio molecular dynamics approaches and empirical models. We demonstrate our method by modeling a femtosecond-pulse laser incident on a flat copper slab for a range of intensities. PMID:26393696

  19. A quantitative model for heat pulse propagation across large helical device plasmas

    NASA Astrophysics Data System (ADS)

    Zhu, H.; Dendy, R. O.; Chapman, S. C.; Inagaki, S.

    2015-06-01

    It is known that rapid edge cooling of magnetically confined plasmas can trigger heat pulses that propagate rapidly inward. These can result in large excursion, either positive or negative, in the electron temperature at the core. A set of particularly detailed measurements was obtained in Large Helical Device (LHD) plasmas [S. Inagaki et al., Plasma Phys. Controlled Fusion 52, 075002 (2010)], which are considered here. By applying a travelling wave transformation, we extend the model of Dendy et al., Plasma Phys. Controlled Fusion 55, 115009 (2013), which successfully describes the local time-evolution of heat pulses in these plasmas, to include also spatial dependence. The new extended model comprises two coupled nonlinear first order differential equations for the (x, t) evolution of the deviation from steady state of two independent variables: the excess electron temperature gradient and the excess heat flux, both of which are measured in the LHD experiments. The mathematical structure of the model equations implies a formula for the pulse velocity, defined in terms of plasma quantities, which aligns with empirical expectations and is within a factor of two of the measured values. We thus model spatio-temporal pulse evolution, from first principles, in a way which yields as output the spatiotemporal evolution of the electron temperature, which is also measured in detail in the experiments. We compare the model results against LHD datasets using appropriate initial and boundary conditions. Sensitivity of this nonlinear model with respect to plasma parameters, initial conditions, and boundary conditions is also investigated. We conclude that this model is able to match experimental data for the spatio-temporal evolution of the temperature profiles of these pulses, and their propagation velocities, across a broad radial range from r /a ≃0.5 to the plasma core. The model further implies that the heat pulse may be related mathematically to soliton solutions of the

  20. Velocity field near the jet orifice of a round jet in a crossflow

    NASA Technical Reports Server (NTRS)

    Fearn, R. L.; Benson, J. P.

    1979-01-01

    Experimentally determined velocities at selected locations near the jet orifice are presented and analyzed for a round jet in crossflow. Jet-to-crossflow velocity ratios of four and eight were studied experimentally for a round subsonic jet of air exhausting perpendicularly through a flat plate into a subsonic crosswind of the same temperature. Velocity measurements were made in cross sections to the jet plume located from one to four jet diameters from the orifice. Jet centerline and vortex properties are presented and utilized to extend the results of a previous study into the region close to the jet orifice.

  1. Effect of grazing flow on the acoustic impedance of interacting cavity-backed orifices

    NASA Technical Reports Server (NTRS)

    Hersh, A. S.; Walker, B.

    1977-01-01

    The two-microphone method was used to investigate the impedance of interacting cavity-backed orifices in the presence of a grazing flow; the investigation has relevance for the control of turbomachinery noise generated within jet engines. The number (varied from one to 16), the diameter, and the spacing of the orifices were the chief parameters studied in the experimental program. It was found that interactions between adjacent orifices, while increasing reactance, do not significantly alter resistance. In addition, the grazing flow appears to reduce the rate of increase of the reactance.

  2. Modeling ultrashort-pulse laser ablation of dielectric materials

    SciTech Connect

    Christensen, B. H.; Balling, P.

    2009-04-15

    An approach to modeling ablation thresholds and depths in dielectric materials is proposed. The model is based on the multiple-rate-equation description suggested by Rethfeld [Phys. Rev. Lett. 92, 187401 (2004)]. This model has been extended to include a description of the propagation of the light into the dielectric sample. The generic model is based on only a few experimental quantities that characterize the native material. A Drude model describing the evolution of the dielectric constant owing to an excitation of the electrons in the material is applied. The model is compared to experimental ablation data for different dielectric materials from the literature.

  3. 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.

  4. [Transvaginal hybrid natural orifice translumenal endoscopic surgery appendectomy].

    PubMed

    Wada, Norihito; Tanabe, Minoru; Kataoka, Fumio; Kitagawa, Yuko

    2013-11-01

    Natural orifice translumenal endoscopic surgery (NOTES) is considered the ultimate minimally invasive intervention for visceral disease. The transvaginal route is now the only one that can be used for NOTES procedures in daily clinical practice. We performed hybrid NOTES appendectomy that was preevaluated and approved by the Japan NOTES and Institutional Review Board. A 5-mm trocar was inserted transumbilically and used for laparoscope access. An additional transumbilical 2.3-mm port was placed, through which the surgeon inserted a grasper. We created a transvaginal port with a long 12-mm trocar. Laparoscopic instruments such as a vessel sealing system, surgical staplers, and a retrieval bag were introduced, and the surgical technique consequently became safer, although the access route was limited. The appendix was removed transvaginally. The patient did not need epidural anesthesia or any pain medication. The cosmetic results were better than that of conventional single-port surgery. Triangulation is achieved in this procedure, which makes the surgery easier. To generalize NOTES to many types of surgery and enable it to be performed in men, the transgastric approach is essential. The development of flexible instruments designed for NOTES is also necessary. PMID:24358726

  5. Hybrid natural orifice transluminal endoscopic surgery for ileocecal resection

    PubMed Central

    Takayama, Satoru; Hara, Masayasu; Sato, Mikinori; Takeyama, Hiromitsu

    2012-01-01

    Although laparoscopic colectomy is commonly performed around the world, an operative wound formed during the surgery is large but not sufficient enough to convert for the majority of open surgery. Thus, a certain sized skin incision is required to remove the resected colon. Here we report the case of a pure laparoscopic ileocecal resection which involves transanal specimen extraction. We present a case characterized by a laterally spreading type of tumor of the cecum. We performed a pure laparoscopic ileocecal resection and the resected specimen was removed transanally using colonoscopy. Intracorporeal functional anastomosis was then performed using a flexible linear stapling device under supporting barbed suture traction. The patient was discharged without complications on postoperative day 4. Laparoscopic colectomy performed with minimal incision could essentially increase the usage of this surgical technique. Although our method is restricted to flat or small lesions, we think it is a feasible and realistic solution for minimization of operative invasion because it involves specimen extraction through a natural orifice. PMID:22408718

  6. Modeling for V—O2 reactive sputtering process using a pulsed power supply

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Yu, He; Dong, Xiang; Jiang, Ya-Dong; Chen, Chao; Wu, Ro-Land

    2014-08-01

    In this article, we present a time-dependent model that enables us to describe the dynamic behavior of pulsed DC reactive sputtering and predict the film compositions of VOx prepared by this process. In this modeling, the average current J is replaced by a new parameter of Jeff. Meanwhile, the four species states of V, V2O3, VO2, and V2O5 in the vanadium oxide films are taken into consideration. Based on this work, the influences of the oxygen gas supply and the pulsed power parameters including the duty cycle and frequency on film compositions are discussed. The model suggests that the time to reach process equilibrium may vary substantially depending on these parameters. It is also indicated that the compositions of VOx films are quite sensitive to both the reactive gas supply and the duty cycle when the power supply works in pulse mode. The ‘steady-state’ balance values obtained by these simulations show excellent agreement with the experimental data, which indicates that the experimentally obtained dynamic behavior of the film composition can be explained by this time-dependent modeling for pulsed DC reactive sputtering process. Moreover, the computer simulation results indicate that the curves will essentially yield oscillations around the average value of the film compositions with lower pulse frequency.

  7. A residue-based toxicokinetic model for pulse-exposure toxicity in aquatic systems

    SciTech Connect

    Hickie, B.E.; McCarty, L.S.; Dixon, D.G.

    1995-12-01

    This pulse-exposure model (PULSETOX) is based on the simple one-compartment first-order kinetics (1CFOK) equation. It tracks the accumulation of waterborne organic chemicals by fish and predicts acute toxicity by means of previously established relationships between whole-body residues and lethality. The predictive capabilities of the model were tested with a data set of 27 acute pulse-exposure lethality tests with larval fathead minnows (Pimephales promelas) exposed to pentachlorophenol (PCP). Tests included eight single exposures (2 to 96 h) and 19 multiple exposures, which varied in the number (2 to 15) and duration (2 to 24 h) of pulses, and time interval between pulses (6 to 24 h). Experimental work included determination of 1CFOK kinetics parameters from [{sup 14}C]PCP uptake and clearance, and from time-toxicity curves. Lethality was expected in any exposure regime where the fish reaches or exceeds the critical body residue (CBR) of 0.30 mmol PCP/kg fish (SD, {+-} 0.02; n = 11). Using the CBR endpoint, the model accounted for between 90 and 93% of variability in the observed lethality data, depending on the toxicokinetic parameters employed. Predictive power of the model was optimized by using kinetics parameters derived from the toxicity curve for pulse-toxicity tests as shown by the regression: predicted LC50 = 1.04 {center_dot} (observed LC50) + 0.01 (p < 0.001, r{sup 2} = 0.94, n = 27).

  8. The Effect of Ionospheric Models on Electromagnetic Pulse Locations

    SciTech Connect

    Fenimore, Edward E.; Triplett, Laurie A.

    2014-07-01

    Locations of electromagnetic pulses (EMPs) determined by time-of-arrival (TOA) often have outliers with significantly larger errors than expected. In the past, these errors were thought to arise from high order terms in the Appleton-Hartree equation. We simulated 1000 events randomly spread around the Earth into a constellation of 22 GPS satellites. We used four different ionospheres: “simple” where the time delay goes as the inverse of the frequency-squared, “full Appleton-Hartree”, the “BobRD integrals” and a full raytracing code. The simple and full Appleton-Hartree ionospheres do not show outliers whereas the BobRD and raytracing do. This strongly suggests that the cause of the outliers is not additional terms in the Appleton-Hartree equation, but rather is due to the additional path length due to refraction. A method to fix the outliers is suggested based on fitting a time to the delays calculated at the 5 GPS frequencies with BobRD and simple ionospheres. The difference in time is used as a correction to the TOAs.

  9. Three-dimensional electromagnetic model of the pulsed-power Z-pinch accelerator

    NASA Astrophysics Data System (ADS)

    Rose, D. V.; Welch, D. R.; Madrid, E. A.; Miller, C. L.; Clark, R. E.; Stygar, W. A.; Savage, M. E.; Rochau, G. A.; Bailey, J. E.; Nash, T. J.; Sceiford, M. E.; Struve, K. W.; Corcoran, P. A.; Whitney, B. A.

    2010-01-01

    A three-dimensional, fully electromagnetic model of the principal pulsed-power components of the 26-MA ZR accelerator [D. H. McDaniel , in Proceedings of the 5th International Conference on Dense Z-Pinches (AIP, New York, 2002), p. 23] has been developed. This large-scale simulation model tracks the evolution of electromagnetic waves through the accelerator’s intermediate-storage capacitors, laser-triggered gas switches, pulse-forming lines, water switches, triplate transmission lines, and water convolute to the vacuum insulator stack. The insulator-stack electrodes are coupled to a transmission-line circuit model of the four-level magnetically insulated vacuum-transmission-line section and double-post-hole convolute. The vacuum-section circuit model is terminated by a one-dimensional self-consistent dynamic model of an imploding z-pinch load. The simulation results are compared with electrical measurements made throughout the ZR accelerator, and are in good agreement with the data, especially for times until peak load power. This modeling effort demonstrates that 3D electromagnetic models of large-scale, multiple-module, pulsed-power accelerators are now computationally tractable. This, in turn, presents new opportunities for simulating the operation of existing pulsed-power systems used in a variety of high-energy-density-physics and radiographic applications, as well as even higher-power next-generation accelerators before they are constructed.

  10. Electrochemical machining with ultrashort voltage pulses: modelling of charging dynamics and feature profile evolution.

    PubMed

    Kenney, Jason A; Hwang, Gyeong S

    2005-07-01

    A two-dimensional computational model is developed to describe electrochemical nanostructuring of conducting materials with ultrashort voltage pulses. The model consists of (1) a transient charging simulation to describe the evolution of the overpotentials at the tool and workpiece surfaces and the resulting dissolution currents and (2) a feature profile evolution tool which uses the level set method to describe either vertical or lateral etching of the workpiece. Results presented include transient currents at different separations between tool and workpiece, evolution of overpotentials and dissolution currents as a function of position along the workpiece, and etch profiles as a function of pulse duration. PMID:21727446

  11. Design and Modeling of Pulsed Power Accelerators Via Circuit Analysis

    Energy Science and Technology Software Center (ESTSC)

    1996-12-05

    SCREAMER simulates electrical circuits which may contain elements of variable resistance, capacitance and inductance. The user may add variable circuit elements in a simulation by choosing from a library of models or by writing a subroutine describing the element. Transmission lines, magnetically insulated transmission lines (MITLs) and arbitrary voltage and current sources may also be included. Transmission lines are modeled using pi-sections connected in series. Many models of switches and loads are included.

  12. Numerical modeling of ozone production in a pulsed homogeneous discharge: A parameter study

    SciTech Connect

    Nilsson, J.O.; Eninger, J.E.

    1997-02-01

    The pulsed volume discharge is an alternative for the efficient generation of ozone in compact systems. This paper presents a parameter study of the reactions in this kind of homogeneous discharge by using a numerical model which solves plasma chemical kinetic rate and energy equations. Results are presented of ozone generation efficiency versus ozone concentration for different parameter combinations. Two parameter regimes are identified and analyzed. In the plasma phase ozone formation regime, where significant amounts of ozone are produced during the discharge pulse, it is found that higher ozone concentrations can be obtained than in the neutral phase ozone formation regime, where most of the ozone is formed after the discharge pulse. In the two-step ozone formation process, the rate of conversion of atomic oxygen plays a key role. In both regimes the ozone generation efficiency increases as n is increased or T{sub 0} decreased. The maximum concentration is 3% at 10 amagat and 100 K. The results on ozone accumulation in multiple pulse discharges are presented. In contrast to the single pulse case, higher efficiency is achieved at lower gas density. This scaling can be explained by losses due to ion currents. A tradeoff can be made between ozone generation efficiency and the number of pulses required to reach a certain concentration.

  13. A Gaussian Model-Based Probabilistic Approach for Pulse Transit Time Estimation.

    PubMed

    Jang, Dae-Geun; Park, Seung-Hun; Hahn, Minsoo

    2016-01-01

    In this paper, we propose a new probabilistic approach to pulse transit time (PTT) estimation using a Gaussian distribution model. It is motivated basically by the hypothesis that PTTs normalized by RR intervals follow the Gaussian distribution. To verify the hypothesis, we demonstrate the effects of arterial compliance on the normalized PTTs using the Moens-Korteweg equation. Furthermore, we observe a Gaussian distribution of the normalized PTTs on real data. In order to estimate the PTT using the hypothesis, we first assumed that R-waves in the electrocardiogram (ECG) can be correctly identified. The R-waves limit searching ranges to detect pulse peaks in the photoplethysmogram (PPG) and to synchronize the results with cardiac beats--i.e., the peaks of the PPG are extracted within the corresponding RR interval of the ECG as pulse peak candidates. Their probabilities of being the actual pulse peak are then calculated using a Gaussian probability function. The parameters of the Gaussian function are automatically updated when a new pulse peak is identified. This update makes the probability function adaptive to variations of cardiac cycles. Finally, the pulse peak is identified as the candidate with the highest probability. The proposed approach is tested on a database where ECG and PPG waveforms are collected simultaneously during the submaximal bicycle ergometer exercise test. The results are promising, suggesting that the method provides a simple but more accurate PTT estimation in real applications. PMID:25420274

  14. A capacitive-pulse model for nanoparticle sensing by single conical nanochannels

    NASA Astrophysics Data System (ADS)

    Sheng, Qian; Wang, Xinwei; Xie, Yanbo; Wang, Ceming; Xue, Jianming

    2016-01-01

    Nanochannel based devices have been widely used for single-molecule detection. The detection usually relies on the resistive-pulse model, where the change of the monitored current depends on the physical volumetric blocking of the nanochannel by the analyte. However, this mechanism requires that the nanochannel diameter should not be much larger than the analyte size, because, otherwise, the resultant current change would be too small to detect, and therefore poses particular challenges for the fabrication of nanochannels. To circumvent this issue, in this report, we propose a different mechanism of capacitive-pulse model, where the transport signals can be significantly magnified by the capacitive effect of the nanochannel. We experimentally demonstrate that current pulses with an averaged peak height of 0.87 nA can be achieved for transporting 60 nm nanoparticles through a conical nanochannel device, whereas the traditional resistive-pulse model only predicts one-order-of-magnitude lowered value. With further comprehensive simulation, the dependence of this effect on the nanochannel geometry as well as the surface charge density for both the nanochannel and the analyte is predicted, which would provide important guidance for better designing of the nanochannel-based sensors.Nanochannel based devices have been widely used for single-molecule detection. The detection usually relies on the resistive-pulse model, where the change of the monitored current depends on the physical volumetric blocking of the nanochannel by the analyte. However, this mechanism requires that the nanochannel diameter should not be much larger than the analyte size, because, otherwise, the resultant current change would be too small to detect, and therefore poses particular challenges for the fabrication of nanochannels. To circumvent this issue, in this report, we propose a different mechanism of capacitive-pulse model, where the transport signals can be significantly magnified by the

  15. MODELING NANOCRYSTALLINE GRAIN GROWTH DURING THE PULSED ELECTRODEPOSITION OF GOLD-COPPER

    SciTech Connect

    Jankowski, A F

    2005-10-27

    The process parameters of current density, pulse duration, and cell potential affect both the structure and composition of electrodeposits. The mechanism for nucleation and growth as determined from current transients yield relationships for nucleus density and nucleation rate. To develop an understanding of the role of the process parameters on grain size, as a design structural parameter to control strength for example, a formulation is presented to model the affects of the deposition energy on grain size and morphology. An activation energy for the deposition process is modeled that reveals different growth mechanisms, wherein nucleation and diffusion effects are each dominant as dependent upon pulse duration. A diffusion coefficient common for each of the pulsed growth modes demarcates an observed transition in growth from smooth to rough surfaces.

  16. Modeling the Pulse Line Ion Accelerator (PLIA): an algorithm for quasi-static field solution.

    SciTech Connect

    Friedman, A; Briggs, R J; Grote, D P; Henestroza, E; Waldron, W L

    2007-06-18

    The Pulse-Line Ion Accelerator (PLIA) is a helical distributed transmission line. A rising pulse applied to the upstream end appears as a moving spatial voltage ramp, on which an ion pulse can be accelerated. This is a promising approach to acceleration and longitudinal compression of an ion beam at high line charge density. In most of the studies carried out to date, using both a simple code for longitudinal beam dynamics and the Warp PIC code, a circuit model for the wave behavior was employed; in Warp, the helix I and V are source terms in elliptic equations for E and B. However, it appears possible to obtain improved fidelity using a ''sheath helix'' model in the quasi-static limit. Here we describe an algorithmic approach that may be used to effect such a solution.

  17. Scintillation event energy measurement via a pulse model based iterative deconvolution method

    NASA Astrophysics Data System (ADS)

    Deng, Zhenzhou; Xie, Qingguo; Duan, Zhiwen; Xiao, Peng

    2013-11-01

    This work focuses on event energy measurement, a crucial task of scintillation detection systems. We modeled the scintillation detector as a linear system and treated the energy measurement as a deconvolution problem. We proposed a pulse model based iterative deconvolution (PMID) method, which can process pileup events without detection and is adaptive for different signal pulse shapes. The proposed method was compared with digital gated integrator (DGI) and digital delay-line clipping (DDLC) using real world experimental data. For singles data, the energy resolution (ER) produced by PMID matched that of DGI. For pileups, the PMID method outperformed both DGI and DDLC in ER and counts recovery. The encouraging results suggest that the PMID method has great potentials in applications like photon-counting systems and pulse height spectrometers, in which multiple-event pileups are common.

  18. Analysis of an SIR Epidemic Model with Pulse Vaccination and Distributed Time Delay

    PubMed Central

    Gao, Shujing; Teng, Zhidong; Nieto, Juan J.; Torres, Angela

    2007-01-01

    Pulse vaccination, the repeated application of vaccine over a defined age range, is gaining prominence as an effective strategy for the elimination of infectious diseases. An SIR epidemic model with pulse vaccination and distributed time delay is proposed in this paper. Using the discrete dynamical system determined by the stroboscopic map, we obtain the exact infection-free periodic solution of the impulsive epidemic system and prove that the infection-free periodic solution is globally attractive if the vaccination rate is larger enough. Moreover, we show that the disease is uniformly persistent if the vaccination rate is less than some critical value. The permanence of the model is investigated analytically. Our results indicate that a large pulse vaccination rate is sufficient for the eradication of the disease. PMID:18322563

  19. Small-Scale Spray Releases: Orifice Plugging Test Results

    SciTech Connect

    Mahoney, Lenna A.; Gauglitz, Phillip A.; Blanchard, Jeremy; Kimura, Marcia L.; Kurath, Dean E.

    2012-09-01

    One of the events postulated in the hazard analysis at the Waste Treatment and Immobilization Plant (WTP) and other U.S. Department of Energy (DOE) nuclear facilities, is a breach in process piping that produces aerosols with droplet sizes in the respirable range. The current approach for predicting the size and concentration of aerosols produced in a spray leak involves extrapolating from correlations published in the literature. These correlations are based on results obtained from small engineered spray nozzles using pure liquids with Newtonian fluid behavior. The narrow ranges of physical properties on which the correlations are based do not cover the wide range of slurries and viscous materials present in the WTP and across processing facilities in the DOE complex. Two key technical areas were identified where testing results were needed to improve the technical basis by reducing the uncertainty introduced by extrapolating existing literature results. The first technical need was to quantify the role of slurry particles in small breaches in which the slurry particles may plug and result in substantially reduced, or even negligible, respirable fraction formed by high pressure sprays. The second technical need was to determine the aerosol droplet size distribution and volume from prototypic breaches and fluids, specifically including sprays from larger breaches with slurries where data from the literature are largely absent. To address these technical areas, small- and large-scale test stands were constructed and operated with simulants to determine the aerosol release fractions and aerosol generation rates from a range of breach sizes and geometries. The properties of the simulants represented the range of properties expected in the WTP process streams and included water, sodium salt solutions, slurries containing boehmite or gibbsite, and a hazardous chemical simulant. The effect of anti-foam agents (AFA) was assessed with most of the simulants. Orifices

  20. Recent advances in natural orifice transluminal endoscopic surgery†.

    PubMed

    Yip, Hon-chi; Chiu, Philip Wai-yan

    2016-01-01

    Natural orifice transluminal endoscopic surgery (NOTES) has emerged as one of the most exciting areas in the field of minimally invasive surgery during the last decade. NOTES comprises a wide spectrum of procedures from various natural accesses such as transgastric or transvaginal routes, and different direct-target or distant-target organs. Since polypectomy was first performed in 1955, major advances in technology and refinement of endoscopic technique have allowed endoscopic surgeons to perform complex endoscopic interventions such as endoscopic submucosal dissection. Recognizing the safety and feasibility of submucosal tunnelling and mucosal closure, endoscopic resection beyond the level of mucosa has been increasingly reported. One of these procedures, peroral endoscopic myotomy for achalasia, has gained much popularity and excellent results have been published comparable with that of traditional Heller's cardiomyotomy. Submucosal tunnelling endoscopic resection has also been reported for tumours situated in the muscular layer of the gastrointestinal tract. To overcome the difficulty of intestinal closure after NOTES, researchers have collaborated with the industry in developing different endoscopic suturing devices such as the Eagle Claw (Olympus Medical Systems, Tokyo, Japan) and Overstitch™ (Apollo Endosurgery, Austin TX, USA). These devices allow precise and secure suture application with the ordinary flexible endoscope, achieving tissue approximation similar to open surgical suturing. To further expand the potential of NOTES, investigators had also developed multitasking platforms enabling the performance of surgical procedures of even higher complexity. Recently, a novel endoscopic robotic system 'Master and Slave Transluminal Endoscopic Robot' (MASTER) has been developed. Early results of endoscopic resection utilizing this system have been encouraging, allowing both experts and novices in endoscopy to perform difficult endoscopic resection with a

  1. Natural orifice translumenal endoscopic surgery applications in clinical practice

    PubMed Central

    Coomber, Ross S; Sodergren, Mikael H; Clark, James; Teare, Julian; Yang, Guang-Zhong; Darzi, Ara

    2012-01-01

    To review natural orifice translumenal endoscopic surgery (NOTES) applications in clinical practice and assess the evidence base for each application as reported in the literature. An electronic literature search was performed. Inclusion criteria were publications relating to NOTES applications in humans. For each type of operation the highest level of evidence available for clinical NOTES publications was evaluated. Morbidity and short-term operative outcomes were compared with gold standard published evidence where available. Finally, registered trials recruiting patients for NOTES applications were identified. Human NOTES publications with the highest level of evidence in each application are identified. There were no RCTs in the literature to date. The strongest evidence came in the form of large, multi-centre trials with 300-500 patients. The results are encouraging, comparable with gold standard techniques on morbidity and mortality. While short-term operative outcomes were also similar when compared to the gold standard techniques, other than improved cosmesis little else can definitely be concluded as a clear benefit of a NOTES procedure. The most common procedures are cholecystectomy, appendicectomy and peritoneoscopy mainly performed via transvaginal access. It is evident that morbidity appears to be higher when the transgastric route is used. The safety profile of hybrid NOTES transvaginal procedures is beginning to be confirmed as is evident from the large number of procedures presented in this review. A number of authors have presented work on pure NOTES procedures but the results are inconsistent and thus the vast majority of NOTES procedures worldwide are performed in a hybrid fashion with a variable amount of laparoscopy. This review of the clinical applications of NOTES summarises the growing evidence behind this surgical discipline and highlights NOTES procedures with an acceptable safety profile. PMID:22442743

  2. Pressure and flow characteristics of restrictive flow orifice devices.

    SciTech Connect

    Shrouf, Roger D.

    2003-06-01

    A Restrictive Flow Orifice (RFO) can be used to enhance the safe design of a pressure system in several ways. Pressure systems frequently incorporate a regulator and relief valve to protect the downstream equipment from accidental overpressure caused by regulator failure. Analysis frequently shows that in cases of high-flow regulator failure, the downstream pressure may rise significantly above the set pressure of the relief valve. This is due to limited flow capacity of the relief valve. A different regulator or relief valve may need to be selected. A more economical solution to this problem is to use an RFO to limit the maximum system flow to acceptable limits within the flow capacity of the relief valve, thereby enhancing the overpressure protection of laboratory equipment. An RFO can also be used to limit the uncontrolled release of system fluid (gas or liquid) upon component or line failure. As an example, potential asphyxiation hazards resultant from the release of large volumes of inert gas from a 'house' nitrogen system can be controlled by the use of an RFO. This report describes a versatile new Sandia-designed RFO available from the Swagelok Company and specifies the gas flow characteristics of this device. Two sizes, 0.010 and 0.020 inch diameter RFOs are available. These sizes will allow enhanced safety for many common applications. This new RFO design are now commercially available and provide advantages over existing RFOs: a high pressure rating (6600 psig); flow through the RFO is equal for either forward or reverse directions; they minimize the potential for leakage by incorporating the highest quality threaded connections; and can enhance the safety of pressure systems.

  3. Model for a pulsed terahertz quantum cascade laser under optical feedback.

    PubMed

    Agnew, Gary; Grier, Andrew; Taimre, Thomas; Lim, Yah Leng; Bertling, Karl; Ikonić, Zoran; Valavanis, Alexander; Dean, Paul; Cooper, Jonathan; Khanna, Suraj P; Lachab, Mohammad; Linfield, Edmund H; Davies, A Giles; Harrison, Paul; Indjin, Dragan; Rakić, Aleksandar D

    2016-09-01

    Optical feedback effects in lasers may be useful or problematic, depending on the type of application. When semiconductor lasers are operated using pulsed-mode excitation, their behavior under optical feedback depends on the electronic and thermal characteristics of the laser, as well as the nature of the external cavity. Predicting the behavior of a laser under both optical feedback and pulsed operation therefore requires a detailed model that includes laser-specific thermal and electronic characteristics. In this paper we introduce such a model for an exemplar bound-to-continuum terahertz frequency quantum cascade laser (QCL), illustrating its use in a selection of pulsed operation scenarios. Our results demonstrate significant interplay between electro-optical, thermal, and feedback phenomena, and that this interplay is key to understanding QCL behavior in pulsed applications. Further, our results suggest that for many types of QCL in interferometric applications, thermal modulation via low duty cycle pulsed operation would be an alternative to commonly used adiabatic modulation. PMID:27607659

  4. Prospects for measuring neutron-star masses and radii with X-ray pulse profile modeling

    SciTech Connect

    Psaltis, Dimitrios; Özel, Feryal; Chakrabarty, Deepto E-mail: fozel@email.arizona.edu

    2014-06-01

    Modeling the amplitudes and shapes of the X-ray pulsations observed from hot, rotating neutron stars provides a direct method for measuring neutron-star properties. This technique constitutes an important part of the science case for the forthcoming NICER and proposed LOFT X-ray missions. In this paper, we determine the number of distinct observables that can be derived from pulse profile modeling and show that using only bolometric pulse profiles is insufficient for breaking the degeneracy between inferred neutron-star radius and mass. However, we also show that for moderately spinning (300-800 Hz) neutron stars, analysis of pulse profiles in two different energy bands provides additional constraints that allow a unique determination of the neutron-star properties. Using the fractional amplitudes of the fundamental and the second harmonic of the pulse profile in addition to the amplitude and phase difference of the spectral color oscillations, we quantify the signal-to-noise ratio necessary to achieve a specified measurement precision for neutron star radius. We find that accumulating 10{sup 6} counts in a pulse profile is sufficient to achieve a ≲ 5% uncertainty in the neutron star radius, which is the level of accuracy required to determine the equation of state of neutron-star matter. Finally, we formally derive the background limits that can be tolerated in the measurements of the various pulsation amplitudes as a function of the system parameters.

  5. Traveling pulses in a stochastic neural field model of direction selectivity.

    PubMed

    Bressloff, Paul C; Wilkerson, Jeremy

    2012-01-01

    We analyze the effects of extrinsic noise on traveling pulses in a neural field model of direction selectivity. The model consists of a one-dimensional scalar neural field with an asymmetric weight distribution consisting of an offset Mexican hat function. We first show how, in the absence of any noise, the system supports spontaneously propagating traveling pulses that can lock to externally moving stimuli. Using a separation of time-scales and perturbation methods previously developed for stochastic reaction-diffusion equations, we then show how extrinsic noise in the activity variables leads to a diffusive-like displacement (wandering) of the wave from its uniformly translating position at long time-scales, and fluctuations in the wave profile around its instantaneous position at short time-scales. In the case of freely propagating pulses, the wandering is characterized by pure Brownian motion, whereas in the case of stimulus-locked pulses, it is given by an Ornstein-Uhlenbeck process. This establishes that stimulus-locked pulses are more robust to noise. PMID:23181018

  6. Traveling pulses in a stochastic neural field model of direction selectivity

    PubMed Central

    Bressloff, Paul C.; Wilkerson, Jeremy

    2012-01-01

    We analyze the effects of extrinsic noise on traveling pulses in a neural field model of direction selectivity. The model consists of a one-dimensional scalar neural field with an asymmetric weight distribution consisting of an offset Mexican hat function. We first show how, in the absence of any noise, the system supports spontaneously propagating traveling pulses that can lock to externally moving stimuli. Using a separation of time-scales and perturbation methods previously developed for stochastic reaction-diffusion equations, we then show how extrinsic noise in the activity variables leads to a diffusive-like displacement (wandering) of the wave from its uniformly translating position at long time-scales, and fluctuations in the wave profile around its instantaneous position at short time-scales. In the case of freely propagating pulses, the wandering is characterized by pure Brownian motion, whereas in the case of stimulus-locked pulses, it is given by an Ornstein–Uhlenbeck process. This establishes that stimulus-locked pulses are more robust to noise. PMID:23181018

  7. The impact assessment of eccentric installation and roughness change in piping on the orifice flow measurement

    SciTech Connect

    Nishi, Y.; Eguchi, Y.; Nishihara, T.; Kanai, T.; Kondo, M.

    2012-07-01

    In orifice flowmeters used in nuclear power plants, requirements for the inner surface roughness of upstream piping and eccentric installation exist depending on certain standards. If these cannot be satisfied based on the installation condition, an appropriate error margin must be considered, although this remains to be clarified. In this research, quantitative data concerning the relative error of orifice flowmeters were obtained during experiments with the parameters of the inner surface roughness of upstream piping and the installation eccentricity of the orifice hole. The maximum Reynolds number of the experimental facility is about 1.6x10{sup 6}. In orifice flowmeters, the flow rate is calculated based on the differential pressure between upstream and downstream orifices and the peculiar discharge coefficient C. The latter value shows an upward trend with increasing roughness of piping, while change of 0.3% of C was observed in terms of roughness (case 2), which approaches the limits of the JIS standard. With significant roughness (Case 3) that exceeds five times the JIS standard, C is shown to have increased by about 1%. No influence was observed by varying the direction of eccentric installation, hence this was fixed and the amount of eccentricity was considered. Change in C of about 0.25% was observed when around twice the standard level of eccentricity was applied. The error margin data under conditions exceeding the JIS standard for the orifice flowmeter was obtained. (authors)

  8. Effect of Orifice Diameter on Bubble Generation Process in Melt Gas Injection to Prepare Aluminum Foams

    NASA Astrophysics Data System (ADS)

    Yuan, Jianyu; Li, Yanxiang; Wang, Ningzhen; Cheng, Ying; Chen, Xiang

    2016-06-01

    The bubble generation process in conditioned A356 alloy melt through submerged spiry orifices with a wide diameter range (from 0.07 to 1.0 mm) is investigated in order to prepare aluminum foams with fine pores. The gas flow rate and chamber pressure relationship for each orifice is first determined when blowing gas in atmospheric environment. The effects of chamber pressure ( P c) and orifice diameter ( D o) on bubble size are then analyzed separately when blowing gas in melt. A three-dimensional fitting curve is obtained illustrating both the influences of orifice diameter and chamber pressure on bubble size based on the experimental data. It is found that the bubble size has a V-shaped relationship with orifice diameter and chamber pressure neighboring the optimized parameter ( D o = 0.25 mm, P c = 0.4 MPa). The bubble generation mechanism is proposed based on the Rayleigh-Plesset equation. It is found that the bubbles will not be generated until a threshold pressure difference is reached. The threshold pressure difference is dependent on the orifice diameter, which determines the time span of pre-formation stage and bubble growth stage.

  9. Effects of surface wettability and edge geometry on drop motion through an orifice

    NASA Astrophysics Data System (ADS)

    Bordoloi, Ankur; Longmire, Ellen

    2012-11-01

    In geothermal energy recovery and CO2 sequestration, drops move through a porous structure by displacing a surrounding liquid. Both the pore geometry and surface wettability influence the drop motion. We simplify the pore structure to a thin plate with a circular orifice. The plate is held horizontally inside a rectangular tank filled with silicone oil. Drops of water/glycerin with Bond numbers (Bo) of 1-10 are released above and axisymmetric to the orifice, encountering the plate after reaching their terminal speed. We use high speed imaging to examine the effects of orifice-to-drop diameter ratio (d/D), orifice surface wettability (hydrophilic/hydrophobic) and edge geometry on the passage of drop fluid through the orifice. We generate regime maps for d/D and Bo delineating domains of drop capture, passage, and passage with breakup. For d/D < 1, sharp edges are observed to yield contact between the drop and orifice so that surface wettability influences the subsequent dynamics. On the other hand, rounded edges appear to prevent direct contact so that the dynamics are unaffected by the surface wettability. Supported by DOE (DOE EERE-PMC-10EE0002764).

  10. Choked flow mechanism of HFC-134a flowing through short-tube orifices

    SciTech Connect

    Nilpueng, Kitti; Wongwises, Somchai

    2011-02-15

    This paper is a continuation of the author's previous work. New experimental data on the occurrence of choked flow phenomenon and mass flow rate of HFC-134a inside short-tube orifices under choked flow condition are presented. Short-tube orifices diameters ranging from 0.406 mm to 0.686 mm with lengths ranging from 1 mm to 3 mm which can be applied to a miniature vapour-compression refrigeration system are examined. The experimental results indicated that the occurrence of choked flow phenomena inside short-tube orifices is different from that obtained from short-tube orifice diameters of greater than 1 mm, which are typically used in air-conditioner. The beginning of choked flow is dependent on the downstream pressure, degree of subcooling, and length-to-diameter ratio. Under choked flow condition, the mass flow rate is greatly varied with the short-tube orifice dimension, but it is slightly affected by the operating conditions. A correlation of mass flow rate through short-tube orifices is proposed in terms of the dimensionless parameters. The predicted results show good agreement with experimental data with a mean deviation of 4.69%. (author) transfer coefficient was also proposed. (author)

  11. New application of temperature-dependent modelling of high temperature superconductors: Quench propagation and pulse magnetization

    NASA Astrophysics Data System (ADS)

    Zhang, Min; Matsuda, Koichi; Coombs, T. A.

    2012-08-01

    We present temperature-dependent modeling of high-temperature superconductors (HTS) to understand HTS electromagnetic phenomena where temperature fluctuation plays a nontrivial role. Thermal physics is introduced into the well-developed H-formulation model, and the effect of temperature-dependent parameters is considered. Based on the model, we perform extensive studies on two important HTS applications: quench propagation and pulse magnetization. A micrometer-scale quench model of HTS coil is developed, which can be used to estimate minimum quench energy and normal zone propagation velocity inside the coil. In addition, we study the influence of inhomogeneity of HTS bulk during pulse magnetization. We demonstrate how the inhomogeneous distribution of critical current inside the bulk results in varying degrees of heat dissipation and uniformity of final trapped field. The temperature-dependent model is proven to be a powerful tool to study the thermally coupled electromagnetic phenomena of HTS.

  12. Nonlocal-thermal-equilibrium model of a pulsed capillary discharge waveguide.

    PubMed

    Broks, B H P; Garloff, K; van der Mullen, J J A M

    2005-01-01

    Slow pulsed capillary discharges are under investigation for use as plasma channel waveguides in laser-wakefield acceleration. In this study, we present a non-local thermal equilibrium (non-LTE) plasma model with a model for the wall temperature coupled to it. This model is used to describe an example of a slow pulsed capillary discharge, and the results are compared with experimental results. The agreement is satisfactory, indicating suitability of our model. Significant deviations from LTE are found during the formation of the plasma channel. The model is also used to study the influence of the discharge current on the guiding properties. It was found that this influence is small over most of the current range that was investigated. PMID:15697729

  13. Comparisons of wing pressure distribution from flight tests of flush and external orifices for Mach numbers from 0.50 to 0.97

    NASA Technical Reports Server (NTRS)

    Montoya, L. C.; Lux, D. P.

    1975-01-01

    Wing pressure distributions obtained in flight with flush orifice and external tubing orifice installations for Mach numbers from 0.50 to 0.97 are compared. The procedure used to install the external tubing orifice is discussed. The results indicate that external tubing orifice installations can give useful results.

  14. High Density Plasma Modeling for Laser and Pulsed-Power Systems

    NASA Astrophysics Data System (ADS)

    Jones, Michael E.

    1997-10-01

    In the Plasma Physics Applications Group at Los Alamos, we have developed a variety of plasma models to study both laser plasma interactions and magnetically driven ``plasmas'' in pulsed-power systems. The parameters for the plasmas range from the collisionless regime of highly ionized, relatively low density (10^19 cm-3) plasma of laser fusion targets to solid metal liners driven by multi-megaAmpere currents. The wide range of parameters, as well as disparate temporal and spatial scales make the modeling these plasmas particularly challenging. For collisionless plasmas, novel Particle-in-Cell methods have been developed. For pulsed-power systems, sophisticated magnetohydrodynamic methods that include material strength and radiation transport are needed. A overview of the various methods and approximations that are used will be given, along with a discussion of methods for modeling the intermediate or semi-collisional regime. Comparison of the models with experiments performed on a number of facilities including the Livermore NOVA laser, the Los Alamos TRIDENT laser, the Sandia PBFA-Z pulsed power facility, and the Los Alamos PEGASUS pulsed-power facility will be given.

  15. [Design and implementation of the pulse wave generator with field programmable gate array based on windkessel model].

    PubMed

    Wang, Hao; Fu, Quanhai; Xu, Lisheng; Liu, Jia; He, Dianning; Li, Qingchun

    2014-10-01

    Pulse waves contain rich physiological and pathological information of the human vascular system. The pulse wave diagnosis systems are very helpful for the clinical diagnosis and treatment of cardiovascular diseases. Accurate pulse waveform is necessary to evaluate the performances of the pulse wave equipment. However, it is difficult to obtain accurate pulse waveform due to several kinds of physiological and pathological conditions for testing and maintaining the pulse wave acquisition devices. A pulse wave generator was designed and implemented in the present study for this application. The blood flow in the vessel was simulated by modeling the cardiovascular system with windkessel model. Pulse waves can be generated based on the vascular systems with four kinds of resistance. Some functional models such as setting up noise types and signal noise ratio (SNR) values were also added in the designed generator. With the need of portability, high speed dynamic response, scalability and low power consumption for the system, field programmable gate array (FPGA) was chosen as hardware platform, and almost all the works, such as developing an algorithm for pulse waveform and interfacing with memory and liquid crystal display (LCD), were implemented under the flow of system on a programmable chip (SOPC) development. When users input in the key parameters through LCD and touch screen, the corresponding pulse wave will be displayed on the LCD and the desired pulse waveform can be accessed from the analog output channel as well. The structure of the designed pulse wave generator is simple and it can provide accurate solutions for studying and teaching pulse waves and the detection of the equipments for acquisition and diagnosis of pulse wave. PMID:25764709

  16. Prediction of flow rates through an orifice at pressures corresponding to the transition between molecular and isentropic flow

    SciTech Connect

    DeMuth, S.F.; Watson, J.S.

    1985-01-01

    A model of compressible flow through an orifice, in the region of transition from free molecular to isentropic expansion flow, has been developed and tested for accuracy. The transitional or slip regime is defined as the conditions where molecular interactions are too many for free molecular flow modeling, yet not great enough for isentropic expansion flow modeling. Due to a lack of literature establishing a well-accepted model for predicting transitional flow, it was felt such work would be beneficial. The model is nonlinear and cannot be satisfactorily linearized for a linear regression analysis. Consequently, a computer routine was developed which minimized the sum of the squares of the residual flow for the nonlinear model. The results indicate an average accuracy within 15% of the measured flow throughout the range of test conditions. Furthermore, the results of the regression analysis indicate that the transitional regime lies between Knudsen numbers of approximately 2 and 45. 4 refs., 3 figs., 1 tab.

  17. Analytical model for interaction of short intense laser pulse with solid target

    SciTech Connect

    Luan, S. X.; Ma, G. J.; Yu, Wei; Yu, M. Y.; Zhang, Q. J.; Sheng, Z. M.; Murakami, M.

    2011-04-15

    A simple but comprehensive two-dimensional analytical model for the interaction of a normally incident short intense laser pulse with a solid-density plasma is proposed. Electron cavitation near the target surface by the laser ponderomotive force induces a strong local electrostatic charge-separation field. The cavitation makes possible mode conversion of the laser light into longitudinal electron oscillation at laser frequency, even for initial normal incidence of laser pulse. The intense charge-separation field in the cavity can significantly enhance the laser induced uxB electron oscillation at twice laser frequency to density levels even higher than that of the initial target.

  18. A dipole model of generating electric pulses in relaxation processes in the Earth's crust

    NASA Astrophysics Data System (ADS)

    Loseva, T. V.; Spivak, A. A.; Kuz'micheva, M. Yu.

    2012-01-01

    A new numerical model of generating electric pulses in the Earth's crust with use of a system of electric dipoles that are located uniformly over an active surface of the structural block relaxing after its constrained turn is developed. Electric moments of dipoles change with time according to the amplitude of differential movements. It is shown that the amplitude of electric pulses and the degree of their attenuation with distance to the source are in agreement with the data of results of instrumental observations.

  19. Three-dimensional reconstruction of subsurface defects using finite-difference modeling on pulsed thermography.

    PubMed

    Ramirez-Granados, J C; Paez, G; Strojnik, M

    2012-06-01

    We develop a technique to analyze pulsed thermography videos in order to detect and reconstruct subsurface defects in homogeneous and layered objects. The technique is based on the analysis of the thermal response of an object to a heat pulse. This thermal response is compared to the predictions of a finite-difference model that is systematically and progressively adjusted to minimize a cost function. With this minimization process, we obtain a depth and a thickness function that allow us to determine the three-dimensional shape, size, depth, thickness, and location of internal defects. The detected defects are reliably reconstructed with graphics of easy interpretation. PMID:22695546

  20. Model-based pulse shape correction for CdTe detectors

    NASA Astrophysics Data System (ADS)

    Bargholtz, Chr.; Fumero, E.; Mårtensson, L.

    1999-02-01

    We present a systematic method to improve energy resolution of CdTe-detector systems with full control of the efficiency. Sampled pulses and multiple amplifier data are fitted by a model of the pulse shape including the deposited energy and the interaction point within the detector as parameters. We show the decisive improvements of spectral resolution and photo-peak efficiency that is obtained without distortion of spectral shape. The information concerning the interaction depth of individual events can be used to discriminate between beta particles and gamma quanta.

  1. Flood pulse alterations and productivity of the Tonle Sap ecosystem: a model for impact assessment.

    PubMed

    Lamberts, Dirk; Koponen, Jorma

    2008-05-01

    Tonle Sap Lake is a large and complex data-deficient ecosystem in the Mekong River Basin. Highly valuable in biodiversity and natural livelihoods capital, it is susceptible to degradation when the flood pulse that drives its productivity is altered as a result of hydropower and irrigation development on the Mekong River. To date, there are no tools to assess the consequences of such flood pulse alterations, leaving the Tonle Sap underrated in water-resources use and planning. A combined ecological-hydrodynamic model is presented for the production potential of the Tonle Sap ecosystem and its likely response to hydrological changes. PMID:18595272

  2. Pressure gradients in oscillating flows in regenerators-analysis and application to pulse-tube refrigerators

    NASA Astrophysics Data System (ADS)

    Mayzus, P.; Fang, L.; Deng, X.; Bauwens, L.

    2002-05-01

    Significant pressure drops are typical in the regenerator, and their impact on performance can be significant. It is clear that irreversibilities associated with viscous friction lower efficiency. But in the pulse-tube, this is perhaps not the most crucial issue. Indeed, by virtue of having only one driven element (the compressor), the pulse-tube is a fairly inflexible device from a design standpoint. Pressure and velocity amplitude and phase determine energy fluxes. Impedances depend upon volume distribution, orifice resistances, and viscous friction in the regenerator. While the combined effect of volume distribution and orifice impedance is relatively easy to analyze, the role of the resistance in the regenerator is harder to deal with. An analysis is presented of the regenerator as an arbitrary porous medium, assuming large pressure gradients. Results are readily incorporated within a small amplitude, harmonic, model of the overall device, including the bypass, if any. For simple assumptions with respect to the temperature profile, such as linear and exponential temperature profiles, closed form solutions are obtained. Results from the model are compared with experiments and their relevance is discussed.

  3. Underwater pulsed laser range-gated imaging model and its effect on image degradation and restoration

    NASA Astrophysics Data System (ADS)

    Youwei, Huang; Fengmei, Cao; Weiqi, Jin; Su, Qiu

    2014-06-01

    The imaging of underwater objects illuminated by artificial light has been of long-standing interest to investigators working in oceanographic environments. Pulsed lasers together with range-gated technology have been widely used for underwater optical imaging applications. In order to describe the formation of underwater range-gated images, a pulsed laser underwater imaging model based on pulse spatial and temporal broadening is proposed. Experiments based on a self-assembled laser range-gated imaging system were implemented in our laboratory. Results show good agreements between experiments and simulations. Both results also confirm higher image contrast toward the tail region of the target-reflected light. Furthermore, experiments on underwater image blur and restoration are also implemented and show good image recovery results. The modulation transfer function-based restoration mechanism also implies a way to eliminate the blur effect caused by light forward scattering.

  4. High pulse rate interferometry using a ruby laser and a cordin model 360 camera

    SciTech Connect

    Deason, V.A.; Epstein, J.S.

    1990-01-01

    This system was originally developed in support of a dynamic diffraction moire effort, but has obvious applications to other types of imaging, interferometry, and high speed optical measurement techniques. The system includes a holographic grade Apollo ruby laser and a Cordin model 330A high speed film camera. The laser has been modified to generate a train of 1 to 100 or more pulses having individual pulse energies of about 40 mJ and a pulse width under 50 ns. The separation between pulses is currently 8 {mu}s, but is expected to soon be reduced to about 1 {mu}s. The laser pulses are synchronized with the framing sync signals from the Cordin camera, so that an individual interferogram is recorded on each of the available frames (a maximum record length of 80 frames is possible). The system is currently configured as a diffraction moire interferometer that illuminates a specimen diffraction grating with a pair of laser beams. The resulting interferograms are recorded using the Cordin camera. The system and the experimental synchronization method are described and some representative experimental data are presented. 1 ref., 5 figs.

  5. Modeling of transient nonequilibrium phenomena in an inductively coupled plasma under pulsed power conditions

    SciTech Connect

    Ye, R.; Ishigaki, T.

    2005-06-15

    A time-dependent two-temperature model is developed to simulate the behavior of an argon radio frequency plasma under transient nonequilibrium conditions, with emphasis to shed light on the temporal and spatial evolution of the nonequilibrium phenomena occurring in pulsed power plasmas. The results show that the effects of changes in input power on the thermal nonequilibrium and the ionization nonequilibrium are most noticeable at the early stages of pulse on and off. The observed deviation from thermal equilibrium during pulsation is more pronounced in the fringes of the plasma and near the wall of the torch. In the central region, the influence is less significant and the plasma remains in a quasilocal thermal equilibrium state. The temporal evolution of the ionization nonequilibrium does not keep pace with that of the thermal nonequilibrium, and the relaxation process of the electron number density is slower and smoother. The effects of operating conditions on the transient behavior of the nonequilibrium situations under pulsed power conditions are also examined. It indicates that, for materials processing, a pulse duration between 2 and 10 ms is adequate for rf plasmas operated in pulse-modulated modes.

  6. Thermal Modeling for Pulsed Inductive FRC Plasmoid Thrusters

    NASA Astrophysics Data System (ADS)

    Pfaff, Michael

    Due to the rising importance of space based infrastructure, long-range robotic space missions, and the need for active attitude control for spacecraft, research into Electric Propulsion is becoming increasingly important. Electric Propulsion (EP) systems utilize electric power to accelerate ions in order to produce thrust. Unlike traditional chemical propulsion, this means that thrust levels are relatively low. The trade-off is that EP thrusters have very high specific impulses (Isp), and can therefore make do with far less onboard propellant than cold gas, monopropellant, or bipropellant engines. As a consequence of the high power levels used to accelerate the ionized propellant, there is a mass and cost penalty in terms of solar panels and a power processing unit. Due to the large power consumption (and waste heat) from electric propulsion thrusters, accurate measurements and predictions of thermal losses are needed. Excessive heating in sensitive locations within a thruster may lead to premature failure of vital components. Between the fixed cost required to purchase these components, as well as the man-hours needed to assemble (or replace) them, attempting to build a high-power thruster without reliable thermal modeling can be expensive. This paper will explain the usage of FEM modeling and experimental tests in characterizing the ElectroMagnetic Plasmoid Thruster (EMPT) and the Electrodeless Lorentz Force (ELF) thruster at the MSNW LLC facility in Redmond, Washington. The EMPT thruster model is validated using an experimental setup, and steady state temperatures are predicted for vacuum conditions. Preliminary analysis of the ELF thruster indicates possible material failure in absence of an active cooling system for driving electronics and for certain power levels.

  7. LAGRANGIAN MODELING OF A SUSPENDED-SEDIMENT PULSE.

    USGS Publications Warehouse

    Schoellhamer, David H.

    1987-01-01

    The one-dimensional Lagrangian Transport Model (LTM) has been applied in a quasi two-dimensional manner to simulate the transport of a slug injection of microbeads in steady experimental flows. A stationary bed segment was positioned below each parcel location to simulate temporary storage of beads on the bottom of the flume. Only one degree of freedom was available for all three bead simulations. The results show the versatility of the LTM and the ability of the LTM to accurately simulate transport of fine suspended sediment.

  8. Simulink based behavioural modelling of a pulse oximeter for deployment in rapid development, prototyping and verification.

    PubMed

    Shokouhian, M; Morling, R C S; Kale, I

    2012-01-01

    The pulse oximeter is a well-known device for measuring the level of oxygen in blood. Since their invention, pulse oximeters have been under constant development in both aspects of hardware and software; however there are still unsolved problems that limit their performance [6], [7]. Many fresh algorithms and new design techniques are being suggested every year by industry and academic researchers which claim that they can improve accuracy of measurements [8], [9]. With the lack of an accurate computer-based behavioural model for pulse oximeters, the only way for evaluation of these newly developed systems and algorithms is through hardware implementation which can be both expensive and time consuming. This paper presents an accurate Simulink based behavioural model for a pulse oximeter that can be used by industry and academia alike working in this area, as an exploration as well as productivity enhancement tool during their research and development process. The aim of this paper is to introduce a new computer-based behavioural model which provides a simulation environment from which new ideas can be rapidly evaluated long before the real implementation. PMID:23367190

  9. Two-photon finite-pulse model for resonant transitions in attosecond experiments

    NASA Astrophysics Data System (ADS)

    Jiménez-Galán, Álvaro; Martín, Fernando; Argenti, Luca

    2016-02-01

    We present an analytical model capable of describing two-photon ionization of atoms with attosecond pulses in the presence of intermediate and final isolated autoionizing states. The model is based on the finite-pulse formulation of second-order time-dependent perturbation theory. It approximates the intermediate and final states with Fano's theory for resonant continua, and it depends on a small set of atomic parameters that can either be obtained from separate ab initio calculations or be extracted from a few selected experiments. We use the model to compute the two-photon resonant photoelectron spectrum of helium below the N =2 threshold for the RABITT (reconstruction of attosecond beating by interference of two-photon transitions) pump-probe scheme, in which an XUV attosecond pulse train is used in association with a weak IR probe, obtaining results in quantitative agreement with those from accurate ab initio simulations. In particular, we show that (i) the use of finite pulses results in a homogeneous redshift of the RABITT beating frequency, as well as a resonant modulation of the beating frequency in proximity to intermediate autoionizing states; (ii) the phase of resonant two-photon amplitudes generally experiences a continuous excursion as a function of the intermediate detuning, with either zero or 2 π overall variation.

  10. The Design of Control Pulses for Heisenberg Always-On Qubit Models

    NASA Astrophysics Data System (ADS)

    Magyar, Rudolph

    2015-03-01

    One model for a universal quantum computer is a spin array with constant nearest neighbor interactions and a controlled unidirectional site-specific magnetic field to generate unitary transformations. This system can be described by a Heisenberg spin Hamiltonian and can be simulated for on the order of 50 spins. It has recently been shown that time-dependent density functional inspired methods may be used to relate various spin models of qubits to ones that may be easier to compute numerically allowing potentially the efficient simulation of greater numbers of spins. One of the challenges of such an agenda is the identification of control pulses that produce desired gate operations (CNOT and single qubit phase gates). We apply control theory to design a universal set of pulses for a Heisenberg always-on model Hamiltonian for a few qubits and compare to known pulses when available. We suggest how this approach may be useful to design control pulses in other realistic designs. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Security Administration under contract DE-AC04-94AL85000.

  11. 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.

  12. a Model for the Parametric Analysis and Optimization of Inertance Tube Pulse Tube Refrigerators

    NASA Astrophysics Data System (ADS)

    Dodson, C.; Lopez, A.; Roberts, T.; Razani, A.

    2008-03-01

    A first order model developed for the design analysis and optimization of Inertance Tube Pulse Tube Refrigerators (ITPTRs) is integrated with the code NIST REGEN 3.2 capable of modeling the regenerative heat exchangers used in ITPTRs. The model is based on the solution of simultaneous non-linear differential equations representing the inertance tube, an irreversibility parameter model for the pulse tube, and REGEN 3.2 to simulate the regenerator. The integration of REGEN 3.2 is accomplished by assuming a sinusoidal pressure wave at the cold side of the regenerator. In this manner, the computational power of REGEN 3.2 is conveniently used to reduce computational time required for parametric analysis and optimization of ITPTRs. The exergy flow and exergy destruction (irreversibility) of each component of ITPTRs is calculated and the effect of important system parameters on the second law efficiency of the refrigerators is presented.

  13. Theoretical modeling of pulse discharge cycle in dielectric barrier discharge plasma actuator

    NASA Astrophysics Data System (ADS)

    Sato, Shintaro; Ohnishi, Naofumi

    2016-07-01

    Simple models based on two-dimensional simulations are proposed to estimate intervals of periodically observed current pulses with a positive-going voltage in a dielectric barrier discharge plasma actuator. There are two distinct peaks in one streamer discharge; one is related to the formation of an ion cloud and the other is related to a filamentary discharge that is identified as a streamer. Simulation results show that the intervals of the current pulses depend on the slope of the applied voltage. For the ion-cloud formation phase, we model the time evolution of electron number density at the exposed electrode with ionization frequency. For the ion-cloud expansion phase, a positive ion cylinder model is proposed to estimate the electric field generated by surface charge on the dielectric. These models well reproduce the discharge intervals obtained in the numerical simulations.

  14. CFD assessment of orifice aspect ratio and mass flow ratio on jet mixing in rectangular ducts

    NASA Technical Reports Server (NTRS)

    Bain, D. B.; Smith, C. E.; Holdeman, J. D.

    1994-01-01

    Isothermal CFD analysis was performed on axially opposed rows of jets mixing with cross flow in a rectangular duct. Laterally, the jets' centerlines were aligned with each other on the top and bottom walls. The focus of this study was to characterize the effects of orifice aspect ratio and jet-to-mainstream mass flow ratio on jet penetration and mixing. Orifice aspect ratios (L/W) of 4-to-1, 2-to-1, and 1-to-1, along with circular holes, were parametrically analyzed. Likewise, jet-to-mainstream mass flow ratios (MR) of 2.0, 0.5, and 0.25 were systematically investigated. The jet-to-mainstream momentum-flux ratio (J) was maintained at 36 for all cases, and the orifice spacing-to-duct height (S/H) was varied until optimum mixing was attained for each configuration. The numerical results showed that orifice aspect ratio (and likewise orifice blockage) had little effect on jet penetration and mixing. Based on mixing characteristics alone, the 4-to-1 slot was comparable to the circular orifice. The 4-to-1 slot has a smaller jet wake which may be advantageous for reducing emissions. However, the axial length of a 4-to-1 slot may be prohibitively long for practical application, especially for MR of 2.0. The jet-to-mainstream mass flow ratio had a more significant effect on jet penetration and mixing. For a 4-to-1 aspect ratio orifice, the design correlating parameter for optimum mixing (C = (S/H)(sq. root J)) varied from 2.25 for a mass flow ratio of 2.0 to 1.5 for a mass flow ratio of 0.25.

  15. Optimization of Orifice Geometry for Cross-Flow Mixing in a Cylindrical Duct

    NASA Technical Reports Server (NTRS)

    Kroll, J. T.; Sowa, W. A.; Samuelsen, G. S.

    1996-01-01

    Mixing of gaseous jets in a cross-flow has significant applications in engineering, one example of which is the dilution zone of a gas turbine combustor. Despite years of study, the design of the jet injection in combustors is largely based on practical experience. The emergence of NO(x) regulations for stationary gas turbines and the anticipation of aero-engine regulations requires an improved understanding of jet mixing as new combustor concepts are introduced. For example, the success of the staged combustor to reduce the emission of NO(x) is almost entirely dependent upon the rapid and complete dilution of the rich zone products within the mixing section. It is these mixing challenges to which the present study is directed. A series of experiments was undertaken to delineate the optimal mixer orifice geometry. A cross-flow to core-flow momentum-flux ratio of 40 and a mass flow ratio of 2.5 were selected as representative of a conventional design. An experimental test matrix was designed around three variables: the number of orifices, the orifice length-to- width ratio, and the orifice angle. A regression analysis was performed on the data to arrive at an interpolating equation that predicted the mixing performance of orifice geometry combinations within the range of the test matrix parameters. Results indicate that the best mixing orifice geometry tested involves eight orifices with a long-to-short side aspect ratio of 3.5 at a twenty-three degree inclination from the center-line of the mixing section.

  16. Exactly solvable two-state quantum model for a pulse of hyperbolic-tangent shape

    NASA Astrophysics Data System (ADS)

    Simeonov, Lachezar S.; Vitanov, Nikolay V.

    2014-04-01

    We present an analytically exactly solvable two-state quantum model, in which the coupling has a hyperbolic-tangent temporal shape and the frequency detuning is constant. The exact solution is expressed in terms of associated Legendre functions. An interesting feature of this model is that the excitation probability does not vanish, except for zero pulse area or zero detuning; this feature is attributed to the asymmetric pulse shape. Two limiting cases are considered. When the coupling rises very slowly, it is nearly linear and the tanh model reduces to the shark model introduced earlier. When the coupling rises very quickly, the tanh model reduces to the Rabi model, which assumes a rectangular pulse shape and hence a sudden switch on. Because of its practical significance, we have elaborated the asymptotics of the solution in the Rabi limit, and we have derived the next terms in the asymptotic expansion, which deliver the corrections to the amplitude and the phase of the Rabi oscillations due to the finite rise time of the coupling.

  17. Pulsed-Field Electrophoresis: Application of a Computer Model to the Separation of Large DNA Molecules

    NASA Astrophysics Data System (ADS)

    Lalande, Marc; Noolandi, Jaan; Turmel, Chantal; Rousseau, Jean; Slater, Gary W.

    1987-11-01

    The biased reptation theory has been applied to the pulsed-field electrophoresis of DNA in agarose gels. A computer simulation of the theoretical model that calculates the mobility of large DNA molecules as a function of agarose pore size, DNA chain properties, and electric field conditions has been used to generate mobility curves for DNA molecules in the size range of the larger yeast chromosomes. Pulsed-field electrophoresis experiments resulting in the establishment of an electrophoretic karyotype for yeast, where the mobility of the DNA fragments is a monotonic function of molecular size for the entire size range that is resolved (200-2200 kilobase pairs), has been compared to the theoretical mobility curves generated by the computer model. The various physical mechanisms and experimental conditions responsible for band inversion and improved electrophoretic separation are identified and discussed in the framework of the model.

  18. Toxicity models of pulsed copper exposure to Pimephales promelas and Daphnia magna.

    PubMed

    Butcher, Jonathan; Diamond, Jerry; Bearr, Jonathan; Latimer, Henry; Klaine, T Stephen J; Hoang, Tham; Bowersox, Marcus

    2006-09-01

    Semiempirical models are useful for interpreting the response of aquatic organisms to toxicants as a function of exposure concentration and duration. Most applications predict cumulative mortality at the end of the test for constant exposure concentrations. Summary measures, such as the median lethal concentration, are then estimated as a function of concentration. Real-world exposures are not constant. Effects may depend on pulse timing, and cumulative analysis based only on integrated exposure concentration is not sufficient to interpret results. We undertook a series of pulsed-exposure experiments using standard toxicological protocols and interpreted the results (mortality, biomass, and reproduction) using a dynamic generalization of a Mancini/Breck--type model that includes two compartments, one for internal concentration as a function of exposure and one for site-of-action concentration or accumulated damage as a function of the internal dose. At exposure concentrations near the effects level, the model explained approximately 50% of the variability in the observed time history of survival, 43% of the change in biomass, and 83% of the variability in net reproduction. Unexplained variability may result from differences in organism susceptibility, amplified by the effects of small sample sizes in standard tests. The results suggest that response is sensitive to prior conditions and that constant-exposure experiments can underestimate the risk from intermittent exposures to the same concentration. For pulsed exposures, neither the average nor the maximum concentration alone is an adequate index of risk, which depends on both the magnitude, duration, and timing of exposure pulses. Better understanding about the impacts of pulsed exposures will require use of experimental protocols with significantly greater numbers of replicates. PMID:16986811

  19. Air release measurements of V-oil 1404 downstream of a micro orifice at choked flow conditions

    NASA Astrophysics Data System (ADS)

    Freudigmann, H.-A.; Iben, U.; Pelz, P. F.

    2015-12-01

    This study presents measurements on air release of V-oil 1404 in the back flow of a micro orifice at choked flow conditions using a shadowgraph imaging method. The released air was determined at three positions downstream of the orifice for different pressure conditions. It was found that more than 23% of the initially dissolved air is released and appears downstream of the orifice in the form of bubbles.

  20. Impact of orifice orientation on a finite-span synthetic jet interaction with a crossflow

    NASA Astrophysics Data System (ADS)

    Van Buren, Tyler; Leong, Chia Min; Whalen, Edward; Amitay, Michael

    2016-03-01

    The formation and evolution of flow structures associated with a finite-span synthetic jet issued into a zero-pressure gradient boundary layer were investigated experimentally using stereoscopic particle image velocimetry. A synthetic jet with an aspect ratio of AR = 18 was mounted on a flat plate and its interaction with a free stream, having a velocity of U∞ = 10 m/s (Reδ = 2000) at momentum coefficients of Cμ = 0.08, 0.33, and 0.75, was studied. The effect of the orifice pitch (α = 20∘-90∘) and skew (β = 0∘-90∘) angles on vortex formation as well as the global impact of the synthetic jet on the flow field was explored in detail. It was found that the orifice orientation had a significant impact on the steady and unsteady flow structures. Different orifice skew and pitch angles could result in several types of vortical structures downstream, including: no coherent vortex structure, a single (positive or negative) strong vortex, or a symmetric vortex pair. In all cases, the velocity near the wall was increased; however, cases with higher blockage (i.e., more wall-normal, transverse orifice) resulted in a strong velocity deficit in the free stream where orifices with lower pitch angles yielded in an increase in velocity throughout. The analysis is concluded with a summary of quantitative metrics that allude to flow control effectiveness.

  1. Apparatus and process for depositing hard coating in a nozzle orifice

    DOEpatents

    Flynn, Paul L.; Giammarise, Anthony W.

    1994-01-01

    The present invention is directed to a process for coating the interior surfaces of an orifice in a substrate that forms a slurry fuel injection nozzle. In a specific embodiment, the nozzle is part of a fuel injection system for metering a coal-water slurry into a large, medium-speed, multi-cylinder diesel engine. In order to retard erosion of the orifice, the substrate is placed in a chemical vapor deposition (CVD) reaction chamber. A reaction gas is passed into the chamber at a gas temperature below its reaction temperature and is directed through the orifice in the substrate. The gas reaction temperature is a temperature at and above which the reaction gas deposits as a coating, and the reaction gas is of a composition whereby improved resistance to erosion by flow of the particulates in the slurry fuel is imparted by the deposited coating. Only the portion of the substrate in proximity to the orifice to be coated is selectively heated to at least the gas reaction temperature for effecting coating of the orifice's interior surfaces by the vapor deposited coating formed from the reaction gas.

  2. Apparatus and process for depositing hard coating in a nozzle orifice

    DOEpatents

    Flynn, P.L.; Giammarise, A.W.

    1994-12-20

    The present invention is directed to a process for coating the interior surfaces of an orifice in a substrate that forms a slurry fuel injection nozzle. In a specific embodiment, the nozzle is part of a fuel injection system for metering a coal-water slurry into a large, medium-speed, multi-cylinder diesel engine. In order to retard erosion of the orifice, the substrate is placed in a chemical vapor deposition (CVD) reaction chamber. A reaction gas is passed into the chamber at a gas temperature below its reaction temperature and is directed through the orifice in the substrate. The gas reaction temperature is a temperature at and above which the reaction gas deposits as a coating, and the reaction gas is of a composition whereby improved resistance to erosion by flow of the particulates in the slurry fuel is imparted by the deposited coating. Only the portion of the substrate in proximity to the orifice to be coated is selectively heated to at least the gas reaction temperature for effecting coating of the orifice's interior surfaces by the vapor deposited coating formed from the reaction gas. 2 figures.

  3. Analysis based on global model of nitrogen plasma produced by pulsed microwave at low pressure

    SciTech Connect

    Qiu, Feng; Yan, Eryan Meng, Fanbao; Ma, Hongge; Liu, Minghai

    2015-07-15

    This paper analyzes certain evolution processes in nitrogen plasmas discharged using pulsed microwaves at low pressure. Comparing the results obtained from the global model incorporating diffusion and the microwave transmission method, the temporal variation of the electron density is analyzed. With a discharge pressure of 300 Pa, the results obtained from experiments and the global model calculation show that when the discharge begins the electron density in the plasma rises quickly, to a level above the critical density corresponding to the discharge microwave frequency, but falls slowly when the discharge microwave pulse is turned off. The results from the global model also show that the electron temperature increases rapidly to a peak, then decays after the electron density reaches the critical density, and finally decreases quickly to room temperature when the discharge microwave pulse is turned off. In the global model, the electron density increases because the high electron temperature induces a high ionization rate. The decay of the electron density mainly comes from diffusion effect.

  4. The pathogenesis of renal dysplasia. II. The significance of lateral and medial ectopy of the ureteric orifice.

    PubMed

    Schwarz, R D; Stephens, F D; Cussen, L J

    1981-09-01

    Renal hypoplasia and dysplasia may be primary malformations linked to a panureteric bud deformity or result from damage to the developing nephrons caused by abnormal urodynamic pressures, Kidneys with misplaced ureteric orifices were graded, according to histologic criteria, on the hypodysplasia scale. With lateral ectopy of the ureteric orifices with and without congenital urethral obstruction, the grades correlated with specific orifice positions. The grades of kidneys with caudal ectopy of the ureters indicated a more general correlation. Dysgenesis of the bud and nephrogenic mesenchyme may account for the renal hypodysplasia when the ureteric orifice is found to be ectopic. PMID:7275560

  5. Modeling of early stages of island growth during pulsed deposition: Role of closed compact islands

    SciTech Connect

    Kotrla, M.; Masin, M.

    2011-03-24

    After a brief review of recent modeling of growth during Pulsed Laser Deposition (PLD), we present the study of a role of adatom interactions on growth of surface islands during PLD in submonolayer regime. We employ kinetic Monte Carlo simulation with reversible growth. Attachment of monomers to islands is irreversible at low temperatures while it becomes reversible at higher temperatures, small islands become unstable with growing temperature. In the case of real system we have to take into account not only diffusion of monomers but also diffusivity of dimers and larger clusters and theirs stability. Our new code allows us to study processes which proceed on different time scales which are typical in PLD experiments: fast deposition (on scale order of 10{sup -5} s) during individual pulses, and relaxation of a system between pulses (on scale order of 0.1 s). We calculate and compare the temperature dependence of island density for two modes pulsed deposition and continuous Molecular Beam Epitaxy (MBE) growth. The island densities in PLD mode are substantially higher than in MBE mode, provided the temperature is sufficiently high. In the case of PLD, we observe anomalous temperature dependence of the island density in a certain temperature interval. It is due to the interplay between a cluster decay time and an interval between pulses. The cluster decay time depends not only on temperature but also on clusters size and shape. The anomalous behavior is caused by the temperature limited stability of the closed--compact clusters. This scenario was revealed for the simplified model with only nearest-neighbor interaction. Now, it is elucidated further and we also include interaction to second and third neighbors. We analyze role of the closed-compact surface island in kinetics of both growth modes. Furthermore, by varying interactions energies, diffusion barrier and parameters of deposition, we compare results of simulations with the PLD experiment for Fe/Mo system.

  6. Preference pulses and the win-stay, fix-and-sample model of choice.

    PubMed

    Hachiga, Yosuke; Sakagami, Takayuki; Silberberg, Alan

    2015-11-01

    Two groups of six rats each were trained to respond to two levers for a food reinforcer. One group was trained on concurrent variable-ratio 20 extinction schedules of reinforcement. The second group was trained on a concurrent variable-interval 27-s extinction schedule. In both groups, lever-schedule assignments changed randomly following reinforcement; a light cued the lever providing the next reinforcer. In the next condition, the light cue was removed and reinforcer assignment strictly alternated between levers. The next two conditions redetermined, in order, the first two conditions. Preference pulses, defined as a tendency for relative response rate to decline to the just-reinforced alternative with time since reinforcement, only appeared during the extinction schedule. Although the pulse's functional form was well described by a reinforcer-induction equation, there was a large residual between actual data and a pulse-as-artifact simulation (McLean, Grace, Pitts, & Hughes, 2014) used to discern reinforcer-dependent contributions to pulsing. However, if that simulation was modified to include a win-stay tendency (a propensity to stay on the just-reinforced alternative), the residual was greatly reduced. Additional modifications of the parameter values of the pulse-as-artifact simulation enabled it to accommodate the present results as well as those it originally accommodated. In its revised form, this simulation was used to create a model that describes response runs to the preferred alternative as terminating probabilistically, and runs to the unpreferred alternative as punctate with occasional perseverative response runs. After reinforcement, choices are modeled as returning briefly to the lever location that had been just reinforced. This win-stay propensity is hypothesized as due to reinforcer induction. PMID:26420769

  7. Suitability research on the cavitation model and numerical simulation of the unsteady pulsed cavitation jet flow

    NASA Astrophysics Data System (ADS)

    Chen, S. Y.; Yu, X. F.; Luan, D. Y.; Qu, Y. P.; Zhou, C.

    2016-05-01

    In order to explore the cavitation jet mechanism, it can first study its critical state of single-phase flow before cavity occurrence to explore the trend of pulsed cavitation jet. Then select the cavitation model to simulate the complex multiphase flow state. Such a step-by-step approach is beneficial to advance research reliably and steady, relying on the foundation for further solving the problem. Three turbulence models such as Euler Hybrid Model, Euler Two Phase Model and Euler Lagrange Model are discussed on their suitability. In this paper, it states only RNG k- ε turbulent model can simulate small scale vortex of jet in the transient simulation. Grid independent verification and the effect of time step is presented. The simulation results show that a large scale vortex ring surrounding jet flow in the nozzle, the pressure of vortex core is slightly lower than the upstream nozzle pressure. Considering the capture ability of small scale eddies, an equivalent pressure is established. The single-phase flow turbulence model is modified to simulate the turbulence flow in the self-excited pulsed cavitation after the cavitation occurs. Through different results comparison of not modified cavitation model and the modified cavitation model to the experimental results, it proves that the latter simulation results are relatively accurate.

  8. Analytic model for the description of above-threshold ionization by an intense short laser pulse

    NASA Astrophysics Data System (ADS)

    Frolov, M. V.; Knyazeva, D. V.; Manakov, N. L.; Geng, Ji-Wei; Peng, Liang-You; Starace, Anthony F.

    2014-06-01

    We present an analytic model for the description of above-threshold ionization (ATI) of an atom by an intense, linearly polarized short laser pulse. Our treatment is based upon a description of ATI by an infinitely long train of short laser pulses whereupon we take the limit that the time interval between pulses becomes infinite. In the quasiclassical approximation, we provide detailed quantum-mechanical derivations, within the time-dependent effective range (TDER) model, of the closed-form formulas for the differential probability P (p) of ATI by an intense, short laser pulse that were presented briefly by Frolov et al. [Phys. Rev. Lett. 108, 213002 (2012), 10.1103/PhysRevLett.108.213002] and that were used to describe key features of the high-energy part of ATI spectra for H and He atoms in an intense, few-cycle laser pulse, using a phenomenological generalization of the physically transparent TDER results to the case of real atoms. Moreover, we extend these results here to the case of an electron bound initially in a p state; we also take into account multiple-return electron trajectories. The ATI amplitude in our approach is given by a coherent sum of partial amplitudes describing ionization by neighboring optical cycles near the peak of the intensity envelope of a short laser pulse. These results provide an analytical explanation of key features in short-pulse ATI spectra, such as the left-right asymmetry in the ionized electron angular distribution, the multiplateau structures, and both large-scale and fine-scale oscillation patterns resulting from quantum interferences of electron trajectories. Our results show that the shape of the ATI spectrum in the middle part of the ATI plateau is sensitive to the spatial symmetry of the initial bound state of the active electron. This sensitivity originates from the contributions of multiple-return electron trajectories. Our analytic results are shown to be in good agreement with results of numerical solutions of the

  9. Numerical modeling of quasitransient backward Raman amplification of laser pulses in moderately undercritical plasmas with multicharged ions

    NASA Astrophysics Data System (ADS)

    Balakin, A. A.; Fisch, N. J.; Fraiman, G. M.; Malkin, V. M.; Toroker, Z.

    2011-10-01

    It was proposed recently that powerful optical laser pulses could be efficiently compressed through backward Raman amplification in ionized low density solids, in spite of strong damping of the resonant Langmuir wave. It was argued that, even for nonsaturated Landau damping of the Langmuir wave, the energy transfer from the pump laser pulse to the amplified seed laser pulse can nevertheless be highly efficient. This work numerically examines such regimes of strong damping, called quasitransient regimes, within the simplest model that takes into account the major effects. The simulations indicate that compression of powerful optical laser pulses in ionized low density solids indeed can be highly efficient.

  10. Computer modeling and experimental study of non-chain pulsed electric-discharge DF laser.

    PubMed

    Ruan, Peng; Xie, Jijiang; Zhang, Laiming; Guo, Jin; Xie, Jingjiang; Yang, Guilong; Li, Dianjun; Pan, Qikun; Tan, Gaijuan; Meng, Fanjiang; Li, Shiming

    2012-12-17

    Computer simulation and experimental study of a pulsed electrical-discharge DF laser pumped by the SF(6)-D(2) non-chain reaction are presented. The computer model encompassing 28 reactions is based on laser rate equations theory, and applied to approximately describe the chemical processes of non-chain DF laser. A comprehensive study of the dependence of number density on time for all particles in the gain area is conducted by numerical calculation adopting Runge-Kutta method. The output performance of non-chain pulsed DF laser as a function of the output mirror reflectivity and the mixture ratio are analyzed. The calculation results are compared with experimental data, showing good agreement with each other. Both the theoretical analysis and experimental results present that the laser output performance can be improved by optimizing the mixture ratio and output mirror reflectivity. The optimum values of mixture ratio and output mirror reflectivity are respectively 10:1 and 30%. The single pulse energy of 4.95J, pulse duration of 148.8ns and peak power of 33.27 MW are achieved under the optimum conditions. PMID:23263131

  11. 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.

  12. Modeling of laser-induced breakdown in dielectrics with subpicosecond pulses

    NASA Astrophysics Data System (ADS)

    Apostolova, T.; Hahn, Y.

    2000-07-01

    Theoretical study of ultrafast laser induced damage by short pulses (τ<1 ps) is carried out on large-band-gap dielectric in an effort to understand the complex physical processes involved. The numerical method of solving a general time-dependent Fokker-Planck type equation for free electron production is discussed in detail. The calculation shows that the collisional avalanche ionization competes with the multiphoton ionization even for pulse length shorter than 25 fs. Sensitivity tests of all the rates in the equation are performed and the most critical ones are identified. From these tests we obtain valuable information in developing new materials that have the desired damage fluence for specific applications. To describe the relaxation of electron plasma, a three body recombination rate is included. Thus, the temporal behavior of the electron density due to a single pulse is treated, as well as the case of exposure to two laser pulses with a time delay between them. The model is only partially successful in reproducing the recent experimental data. Effect of the presence of a linear decay term and optical defects on the damage threshold is considered in the context of the rate equation input.

  13. Comprehensive modeling of structural modification induced by a femtosecond laser pulse inside fused silica glass

    NASA Astrophysics Data System (ADS)

    Najafi, Somayeh; Sadat Arabanian, Atoosa; Massudi, Reza

    2016-06-01

    A comprehensive theoretical model is proposed based on equations describing the nonlinear propagation of an ultrashort pulse inside transparent material, electron density evolution, non-Fourier heat conduction, and thermo-elasto plastic displacement which are respectively solved by various methods. These methods include the split-step finite difference technique and alternating-direction implicit algorithm, fourth-order Range–Kutta algorithm, hybrid finite-element method/finite-difference method, and finite-element method in both space and time to achieve refractive index changes. The whole chain of processes occurring in the interaction of a focused ultrashort laser pulse with fused silica glass in prevalent conditions of micromachining applications is numerically investigated. By optimizing the numerical method and by using an adaptive mesh approach, the execution time of the program is significantly reduced so that the calculations are done at each time step in a fraction of a second. Simulation results show that the energy and duration of the input pulse are very important parameters in induced changes, but the chirp of the input pulse is not an effective parameter. Consequently, by appropriate setting of those parameters one can design a desired refractive index profile.

  14. Electromagnetic pulse from supernovae. [model for old low-mass stars

    NASA Technical Reports Server (NTRS)

    Colgate, S. A.

    1975-01-01

    Upper and lower limits to the radiated electromagnetic pulse from a supernova are calculated assuming that the mass fraction of the matter expanding inside the dipole magnetic field shares energy and maintains the pressure balance in the process. A supernova model is described in which the explosion occurs in old low-mass stars containing less than 10% hydrogen in their ejecta and a remnant neutron star is produced. The analysis indicates that although the surface layer of a star of 1 g/cu thickness may be shock-accelerated to an energy factor of about 100 and may expand into the vacuum with an energy factor approaching 10,000, the equatorial magnetic field will retard this expansion so that the inner, more massive ejecta layers will effectively accelerate the presumed canonical dipole magnetic field to greater velocities than would the surface layer alone. A pulse of 10 to the 46th power ergs in a width of about 150 cm will result which will not be affected by circumstellar matter or electron self-radiation effects. It is shown that interstellar matter will attenuate the pulse, but that charge separation may reduce the attenuation and allow a larger pulse to escape.

  15. Measurement and modeling of dispersive pulse propagation in draw wire waveguides

    NASA Technical Reports Server (NTRS)

    Madaras, Eric I.; Kohl, Thomas W.; Rogers, Wayne P.

    1995-01-01

    An analytical model of dispersive pulse propagation in semi-infinite cylinders due to transient axially symmetric end conditions has been experimentally investigated. Specifically, the dispersive propagation of the first axially symmetric longitudinal mode in thin wire waveguides, which have ends in butt contact with longitudinal piezoelectric ultrasonic transducers, is examined. The method allows for prediction of a propagated waveform given a measured source waveform, together with the material properties of the cylinder. Alternatively, the source waveform can be extracted from measurement of the propagated waveform. The material properties required for implementation of the pulse propagation model are determined using guided wave phase velocity measurements. Hard tempered aluminum 1100 and 304 stainless steel wires, with 127, 305, and 406 micron diam., were examined. In general, the drawn wires were found to behave as transversely isotropic media.

  16. Arterial pulse pressure amplification described by means of a nonlinear wave model: characterization of human aging

    NASA Astrophysics Data System (ADS)

    Alfonso, M.; Cymberknop, L.; Armentano, R.; Pessana, F.; Wray, S.; Legnani, W.

    2016-04-01

    The representation of blood pressure pulse as a combination of solitons captures many of the phenomena observed during its propagation along the systemic circulation. The aim of this work is to analyze the applicability of a compartmental model for propagation regarding the pressure pulse amplification associated with arterial aging. The model was applied to blood pressure waveforms that were synthesized using solitons, and then validated by waveforms obtained from individuals from differentiated age groups. Morphological changes were verified in the blood pressure waveform as a consequence of the aging process (i.e. due to the increase in arterial stiffness). These changes are the result of both a nonlinear interaction and the phenomena present in the propagation of nonlinear mechanic waves.

  17. Measurement and Modeling of Dispersive Pulse Propagation in Drawn Wire Waveguides

    NASA Technical Reports Server (NTRS)

    Madaras, Eric I.; Kohl, Thomas W.; Rogers, Wayne P.

    1995-01-01

    An analytical model of dispersive pulse propagation in semi-infinite cylinders due to transient axially symmetric end conditions has been experimentally investigated. Specifically, the dispersive propagation of the first axially symmetric longitudinal mode in thin wire waveguides, which have ends in butt contact with longitudinal piezoelectric ultrasonic transducers, is examined. The method allows for prediction of a propagated waveform given a measured source waveform, together with the material properties of the cylinder. Alternatively, the source waveform can be extracted from measurement of the propagated waveform. The material properties required for implementation of the pulse propagation model are determined using guided wave phase velocity measurements. Hard tempered aluminum 1100 and 304 stainless steel wires, with 127, 305, and 406 micron diam., were examined. In general, the drawn wires were found to behave as transversely isotropic media.

  18. Application of the k-epsilon turbulence model to the simulation of a fully pulsed free air jet

    NASA Astrophysics Data System (ADS)

    Graham, L. J. W.; Bremhorst, K.

    1993-03-01

    The work describes application of the k-epsilon turbulence model to a fully pulsed air jet. The standard model failed to predict the change in slope of the velocity decay where the jet changes from pulsed to steady jet behavior. A change in one of the constants of the k-epsilon model based on the behavior of the periodic velocity component relative to the intrinsic component yielded satisfactory results. Features of the pulsed jet which were successfully simulated included the flow reversal near the edge of the jet, increased entrainment when compared to steady jets and large radial outflow near the leading edge of the pulse and large radial inflow near the outer edge of the jet for the remainder of the pulse.

  19. Computer and laboratory modeling of radiation-acoustic detector for charged particles pulse beams and plasma parameters measuring

    SciTech Connect

    Kresnin, Yu.A.; Stervoedov, N.G.

    1996-12-31

    Model investigations and laboratory tests of detectors for charged particles pulse beams and plasma parameters measuring are presented. Detector represents combination of classic Faraday cup with electrical way of signal getting and radiation-acoustic meter of pulse beams parameters. Radiation-acoustic meter consists of two parts--thin detector, transparent for beams of high energy particles, and thick detector with full absorption. Ultrasonic oscillations, which arise during interaction of charged particles pulse beams or plasma with detector material, are transformed by piezoelectric detector into electric signals, whose amplitude-frequency and time characteristics functionally depended on beams parameters. All the signals come into microcontroller device Intel MSC51. This device produces calculations of following beam parameters: average energy, pulse charge, pulse currents, density, beam size and pulse time. Calculated characteristics of meter well coincide with experimental measurements, carried out at accelerators in particles energy range from 1 to 100 Mev.

  20. Wall stress and deformation analysis in a numerical model of pulse wave propagation.

    PubMed

    He, Fan; Hua, Lu; Gao, Lijian

    2015-01-01

    To simulate pulse wave propagation, we set up a wave propagation model using blood-wall interaction in previous work. In this paper, our purpose is to investigate wall stress and deformation of the wave propagation model. The finite element method is employed for solving the governing equations of blood and wall. Our results suggest that there are two peaks in the circumferential stress and strain distributions of the normal model. The stress and strain values change with the varieties of different factors, such as wall thickness and vessel diameter. The results indicate that different parameters of fluid and tube wall have remarked impact on wall stress and deformation. PMID:26406044

  1. A statistical model of the photomultiplier gain process with applications to optical pulse detection

    NASA Technical Reports Server (NTRS)

    Tan, H. H.

    1982-01-01

    A Markov diffusion model was used to determine an approximate probability density for the random gain. This approximate density preserves the correct second-order statistics and appears to be in reasonably good agreement with experimental data. The receiver operating curve for a pulse counter detector of PMT cathode emission events was analyzed using this density. The error performance of a simple binary direct detection optical communication system was also derived. Previously announced in STAR as N82-25100

  2. A statistical model of the photomultiplier gain process with applications to optical pulse detection

    NASA Technical Reports Server (NTRS)

    Tan, H. H.

    1982-01-01

    A Markov diffusion model was used to determine an approximate probability density for the random gain. This approximate density preserves the correct second-order statistics and appears to be in reasonably good agreement with experimental data. The receiver operating curve for a pulse counter detector of PMT cathode emission events was analyzed using this density. The error performance of a simple binary direct detection optical communication system was also derived.

  3. Effect of Flow Rate of Side-Type Orifice Intake on Withdrawn Water Temperature

    PubMed Central

    Li, Guangning

    2014-01-01

    Side-type orifice intake is a type of selective withdrawal facility used in managing reservoirs to mitigate the negative effects of low-temperature water. Based on the temperature data of a thermal stratified reservoir in China, an experiment was conducted in flume to study the influence of intake flow rate on withdrawn water temperature with different temperature distributions. Results indicated that withdrawn water temperature changed with different flow rates. The temperature change was determined by the water temperature gradients above and below the intake, whereas the change trend of temperature depended on the difference between the water temperature gradient above and below the intake. We likewise proposed a new equation with which the withdrawn water temperature of a thermal stratified reservoir using a side-type orifice could be calculated. These findings could be directly applied to the design and operation of side-type orifice intake in thermal stratified reservoirs. PMID:25019100

  4. Inactivation of Heterosigma akashiwo in ballast water by circular orifice plate-generated hydrodynamic cavitation.

    PubMed

    Feng, Daolun; Zhao, Jie; Liu, Tian

    2016-01-01

    The discharge of alien ballast water is a well-known, major reason for marine species invasion. Here, circular orifice plate-generated hydrodynamic cavitation was used to inactivate Heterosigma akashiwo in ballast water. In comparison with single- and multihole orifice plates, the conical-hole orifice plate yielded the highest inactivation percentage, 51.12%, and consumed only 6.84% energy (based on a 50% inactivation percentage). Repeating treatment, either using double series-connection or circling inactivation, elevated the inactivation percentage, yet consumed much more energy. The results indicate that conical-hole-generated hydrodynamic cavitation shows great potential as a pre-inactivation method for ballast water treatment. PMID:26370563

  5. Visual study of the effect of grazing flow on the oscillatory flow in a resonator orifice

    NASA Technical Reports Server (NTRS)

    Baumeister, K. J.; Rice, E. J.

    1975-01-01

    Grazing flow and oscillatory flow in an orifice were studied in a plexiglass flow channel with a single side branch Helmholtz resonator using water as the fluid medium. An oscillatory flow was applied to the resonatory cavity, and color dyes were injected in both the orifice and the grazing flow field to record the motion of the fluid. The flow regimes associated with linear and nonlinear (high sound pressure level) impedances with and without grazing flows were recorded by a high-speed motion-picture camera. Appreciable differences in the oscillatory flow field were seen in the various flow regimes. With high grazing flows, the outflow and inflow from the resonator cavity are found to be asymmetric. The visual study confirms that jet energy loss during flow into a resonator cavity is much larger than the loss for ejection from the cavity into the grazing flow. For inflow into the resonator cavity, the effective orifice area was significantly reduced.

  6. Influence of Local Flow Field on Flow Accelerated Corrosion Downstream from an Orifice

    NASA Astrophysics Data System (ADS)

    Utanohara, Yoichi; Nagaya, Yukinori; Nakamura, Akira; Murase, Michio

    Flow accelerated corrosion (FAC) rate downstream from an orifice was measured in a high-temperature water test loop to evaluate the effects of flow field on FAC. Orifice flow was also measured using laser Doppler velocimetry (LDV) and simulated by steady RANS simulation and large eddy simulation (LES). The LDV measurements indicated the flow structure did not depend on the flow velocity in the range of Re = 2.3×104 to 1.2×105. Flow fields predicted by RANS and LES agreed well with LDV data. Measured FAC rate was higher downstream than upstream from the orifice and the maximum appeared at 2D (D: pipe diameter) downstream. The shape of the profile of the root mean square (RMS) wall shear stress predicted by LES had relatively good agreement with the shape of the profile of FAC rate. This result indicates that the effects of flow field on FAC can be evaluated using the calculated wall shear stress.

  7. Electrical pulse induced biological effects using dielectric spectroscopy and mathematical models

    NASA Astrophysics Data System (ADS)

    Garner, Allen Lawrence

    This dissertation studies the effects of pulsed electric fields (PEFs) on biological cells by measuring the changes in the electrical properties of the pulsed cells and mathematically modeling avascular tumor growth, cell population dynamics, and Ohmic heating. These issues are critical because of the recent use of intense ultrashort PEFs for various biological and medical applications. Recent research using PEFs for tumor treatment motivated an investigation of a simple model for the growth of an avascular tumor. We modeled tumor growth before and after necrotic core formation by incorporating spatial dependence into a one dimensional scaling law. This model emphasized the importance of cell metabolic rate in determining the final steady state size of the tumor. Experimental results showing changes in cell survival and cell cycle due to PEFs led to an investigation of a simple mathematical model for cell population dynamics that considered the cells to be proliferating (dividing) or quiescent (resting). Although some cell populations apparently reached steady state quickly, the proliferating cell population fell below one, meaning that the overall cell population would eventually decay away. This result, which was unaltered by including a transition from the quiescent to proliferating state, emphasized the importance of targeting proliferating cells for successful cancer treatments. Time domain dielectric spectroscopy was used to measure the electrical properties of a biological cell suspension over a wide frequency range with a single pulse following multiple PEFs. Fitting the dielectric properties of a cancer cell (Jurkat) suspension to a double shell model yielded the dielectric parameters of the cell membrane, cytoplasm, nuclear envelope, and nucleoplasm. Decreased cytoplasm and nucleoplasm conductivity and increased suspension conductivity suggestion transport from the cell interior to the exterior consistent with electroporation. Reduced cell membrane

  8. Inductive Pulsed Plasma Thruster Model with Time-Evolution of Energy and State Properties

    NASA Technical Reports Server (NTRS)

    Polzin, Kurt A.; Sankaran, Kamesh

    2012-01-01

    A model for pulsed inductive plasma acceleration is presented that consists of a set of circuit equations coupled to both a one-dimensional equation of motion and an equation governing the partitioning of energy. The latter two equations are obtained for the plasma current sheet by treating it as a single element of finite volume and integrating the governing equations over that volume. The integrated terms are replaced where necessary by physically-equivalent quantities that are calculated through the solution of other parts of the governing equation set. The model improves upon previous one-dimensional performance models by permitting the time-evolution of the energy and state properties of the plasma, the latter allowing for the tailoring of the model to different gases that may be chosen as propellants. The time evolution of the various energy modes in the system and the associated plasma properties, calculated for argon propellant, are presented to demonstrate the efficacy of the model. The model produces a result where efficiency is maximized at a given value of the electrodynamic scaling term known as the dynamic impedance parameter. Qualitatively and quantitatively, the model compares favorably with performance measured for two separate inductive pulsed plasma thrusters, with disagreements attributable to simplifying assumptions employed in the generation of the model solution.

  9. Realistic modeling of the pulse profile of PSR J0737-3039A

    SciTech Connect

    Perera, B. B. P.; Kim, C.; McLaughlin, M. A.; Ferdman, R. D.; Kramer, M.; Freire, P. C. C.; Stairs, I. H.; Possenti, A.

    2014-05-20

    The Double Pulsar, PSR J0737-3039A/B, is a unique system in which both neutron stars have been detected as radio pulsars. As shown in Ferdman et al., there is no evidence for pulse profile evolution of the A pulsar, and the geometry of the pulsar was fit well with a double-pole circular radio beam model. Assuming a more realistic polar cap model with a vacuum retarded dipole magnetosphere configuration including special relativistic effects, we create synthesized pulse profiles for A given the best-fit geometry from the simple circular beam model. By fitting synthesized pulse profiles to those observed from pulsar A, we constrain the geometry of the radio beam, namely the half-opening angle and the emission altitude, to be ∼30° and ∼10 neutron star radii, respectively. Combining the observational constraints of PSR J0737-3039A/B, we are able to construct the full three-dimensional orbital geometry of the Double Pulsar. The relative angle between the spin axes of the two pulsars (Δ{sub S}) is estimated to be ∼(138° ± 5°) at the current epoch and will likely remain constant until tidal interactions become important in ∼85 Myr, at merger.

  10. Note: High temperature pulsed solenoid valve.

    PubMed

    Shen, Wei; Sulkes, Mark

    2010-01-01

    We have developed a high temperature pulsed solenoid valve with reliable long term operation to at least 400 degrees C. As in earlier published designs, a needle extension sealing a heated orifice is lifted via solenoid actuation; the solenoid is thermally isolated from the heated orifice region. In this new implementation, superior sealing and reliability were attained by choosing a solenoid that produces considerably larger lifting forces on the magnetically actuated plunger. It is this property that facilitates easily attainable sealing and reliability, albeit with some tradeoff in attainable gas pulse durations. The cost of the solenoid valve employed is quite low and the necessary machining quite simple. Our ultimate level of sealing was attained by making a simple modification to the polished seal at the needle tip. The same sealing tip modification could easily be applied to one of the earlier high T valve designs, which could improve the attainability and tightness of sealing for these implementations. PMID:20113132

  11. Evaluating the use of a continuous approximation for model-based quantification of pulsed chemical exchange saturation transfer (CEST).

    PubMed

    Tee, Y K; Khrapitchev, A A; Sibson, N R; Payne, S J; Chappell, M A

    2012-09-01

    Many potential clinical applications of chemical exchange saturation transfer (CEST) have been studied in recent years. However, due to various limitations such as specific absorption rate guidelines and scanner hardware constraints, most of the proposed applications have yet to be translated into routine diagnostic tools. Currently, pulsed CEST which uses multiple short pulses to perform the saturation is the only viable irradiation scheme for clinical translation. However, performing quantitative model-based analysis on pulsed CEST is time consuming because it is necessary to account for the time dependent amplitude of the saturation pulses. As a result, pulsed CEST is generally treated as continuous CEST by finding its equivalent average field or power. Nevertheless, theoretical analysis and simulations reveal that the resulting magnetization is different when the different irradiation schemes are applied. In this study, the quantification of important model parameters such as the amine proton exchange rate from a pulsed CEST experiment using quantitative model-based analyses were examined. Two model-based approaches were considered - discretized and continuous approximation to the time dependent RF irradiation pulses. The results showed that the discretized method was able to fit the experimental data substantially better than its continuous counterpart, but the smaller fitted error of the former did not translate to significantly better fit for the important model parameters. For quantification of the endogenous CEST effect, such as in amide proton transfer imaging, a model-based approach using the average power equivalent saturation can thus be used in place of the discretized approximation. PMID:22858666

  12. Evaluating the use of a continuous approximation for model-based quantification of pulsed chemical exchange saturation transfer (CEST)

    NASA Astrophysics Data System (ADS)

    Tee, Y. K.; Khrapitchev, A. A.; Sibson, N. R.; Payne, S. J.; Chappell, M. A.

    2012-09-01

    Many potential clinical applications of chemical exchange saturation transfer (CEST) have been studied in recent years. However, due to various limitations such as specific absorption rate guidelines and scanner hardware constraints, most of the proposed applications have yet to be translated into routine diagnostic tools. Currently, pulsed CEST which uses multiple short pulses to perform the saturation is the only viable irradiation scheme for clinical translation. However, performing quantitative model-based analysis on pulsed CEST is time consuming because it is necessary to account for the time dependent amplitude of the saturation pulses. As a result, pulsed CEST is generally treated as continuous CEST by finding its equivalent average field or power. Nevertheless, theoretical analysis and simulations reveal that the resulting magnetization is different when the different irradiation schemes are applied. In this study, the quantification of important model parameters such as the amine proton exchange rate from a pulsed CEST experiment using quantitative model-based analyses were examined. Two model-based approaches were considered - discretized and continuous approximation to the time dependent RF irradiation pulses. The results showed that the discretized method was able to fit the experimental data substantially better than its continuous counterpart, but the smaller fitted error of the former did not translate to significantly better fit for the important model parameters. For quantification of the endogenous CEST effect, such as in amide proton transfer imaging, a model-based approach using the average power equivalent saturation can thus be used in place of the discretized approximation.

  13. Flow characteristics and methods of flow calculation of high-speed compressible flow through pipe orifices

    NASA Astrophysics Data System (ADS)

    Torizumi, Y.; Hirayama, N.; Maeda, T.

    1983-01-01

    Flow characteristics of a compressible gas flow through an orifice are investigated experimentally at pressure ratios below the regulation values of JIS and ASME. For practical mass flow measurements, a theoretical method of mass flow estimations is extended using one-dimensional flow theory and experimental data. Using the method, the accuracy of mass flow measurements with orifice meters is about + or 1% in the Reynolds number range of turbulent flows and also in supercritical flows. Tables of the product of flow coefficient and expansion factor are obtained by the method at various diameter ratios, pressure ratios, and specific heats.

  14. Effect of orifice length-diameter ratio on fuel sprays for compression-ignition engines

    NASA Technical Reports Server (NTRS)

    Gelalles, A G

    1933-01-01

    Experimental results on the effect of the length-diameter ratio of the orifice on the spray characteristics, together with a brief analysis of the factors affecting these characteristics, are presented in this report. The length-diameter ratios tested ranged from 0.5 to 10; the orifice diameters from 0.008 to 0.040 inch; and the injection pressures from 2,000 to 8,000 pounds per square inch. The density of the air into which the fuel was discharged was varied from 0.38 to 1.35 pounds per cubic foot.

  15. Modelling of metal vapour in pulsed TIG including influence of self-absorption

    NASA Astrophysics Data System (ADS)

    Iwao, Toru; Mori, Yusuke; Okubo, Masato; Sakai, Tadashi; Tashiro, Shinichi; Tanaka, Manabu; Yumoto, Motoshige

    2010-11-01

    Pulsed TIG (tungsten inert gas) welding is used to improve the stability and speed of arc welding, and to allow greater control over the heat input to the weld. The temperature and the radiation power density of the pulsed arc vary as a function of time, as does the distribution of metal vapour, and its effects on the arc. A self-consistent two-dimensional model of the arc and electrodes is used to calculate the properties of the arc as a function of time. Self-absorption of radiation is treated by two methods, one taking into account absorption of radiation only within the control volume of emission, and the other taking into account absorption throughout the plasma. The relation between metal vapour and radiation power density is analysed by calculating the iron vapour distribution. The results show that the transport of iron vapour is strongly affected by the fast convective flow during the peak current period. During the base current period, the region containing a low concentration of metal vapour expands because of the low convective flow. The iron vapour distribution does not closely follow the current pulses. The temperature, iron vapour and radiation power density distributions depend on the self-absorption model used. The temperature distribution becomes broader when self-absorption of radiation from all directions is considered.

  16. Prediction of Bubble Diameter at Detachment from a Wall Orifice in Liquid Cross Flow Under Reduced and Normal Gravity Conditions

    NASA Technical Reports Server (NTRS)

    Nahra, Henry K.; Kamotani, Y.

    2003-01-01

    Bubble formation and detachment is an integral part of the two-phase flow science. The objective of the present work is to theoretically investigate the effects of liquid cross-flow velocity, gas flow rate embodied in the momentum flux force, and orifice diameter on bubble formation in a wall-bubble injection configuration. A two-dimensional one-stage theoretical model based on a global force balance on the bubble evolving from a wall orifice in a cross liquid flow is presented in this work. In this model, relevant forces acting on the evolving bubble are expressed in terms of the bubble center of mass coordinates and solved simultaneously. Relevant forces in low gravity included the momentum flux, shear-lift, surface tension, drag and inertia forces. Under normal gravity conditions, the buoyancy force, which is dominant under such conditions, can be added to the force balance. Two detachment criteria were applicable depending on the gas to liquid momentum force ratio. For low ratios, the time when the bubble acceleration in the direction of the detachment angle is greater or equal to zero is calculated from the bubble x and y coordinates. This time is taken as the time at which all the detaching forces that are acting on the bubble are greater or equal to the attaching forces. For high gas to liquid momentum force ratios, the time at which the y coordinate less the bubble radius equals zero is calculated. The bubble diameter is evaluated at this time as the diameter at detachment from the fact that the bubble volume is simply given by the product of the gas flow rate and time elapsed. Comparison of the model s predictions was also made with predictions from a two-dimensional normal gravity model based on Kumar-Kuloor formulation and such a comparison is presented in this work.

  17. An extended diffusive model for calculating thermal diffusivity from single monopole tokamak heat pulse propagation

    SciTech Connect

    Marinak, M. )

    1990-02-01

    The problem of deducing {chi}{sub e} from measurements of the propagation of a monopole heatpulse is considered. An extended diffusive model, which takes into account perturbed sources and sinks is extended to the case of a monopole heat input. {chi}{sub e} is expressed as a function of two observables, the heat pulse velocity and the radial damping rate. Two simple expressions valid for two different ranges of the radius of the poloidal waist of the beam power profile are given. The expressions are valid in the heat pulse measurement region, extending radially 0.05a beyond the beam power waist to near 0.6a. The inferred {chi}{sub e} is a local value, not an average value of the radial {chi}{sub e} profile. 7 refs., 6 figs., 1 tab.

  18. Model of transient cooperative phenomena triggered by THz-pulse irradiation

    NASA Astrophysics Data System (ADS)

    Ishida, Kunio; Nasu, Keiichiro

    2015-09-01

    We studied the cooperative phenomena induced by injection of coherent phonons by THz optical pulses. Based on the analogy to the photoinduced phase transitions observed in various materials, we consider that cooperative interactions between electrons and coherent phonons will lead to the multiplication of excited electrons and/or growth of a transient phase, which is understood by bifurcation of quantum-mechanical wavepackets on adiabatic potential energy surfaces. Employing a model of localized electrons coupled with a quantized optical phonon mode, we discuss the dynamics of the cooperative phenomena by THz-pulse irradiation and, in particular, the role of the number and/or the initial distribution of phonons in the initial creation process of transient phases.

  19. Modeling of testosterone regulation by pulse-modulated feedback: An experimental data study

    NASA Astrophysics Data System (ADS)

    Mattsson, Per; Medvedev, Alexander

    2013-10-01

    The continuous part of a hybrid (pulse-modulated) model of testosterone feedback regulation is extended with infinite-dimensional and nonlinear dynamics, to better explain the testosterone concentration profiles observed in clinical data. A linear least-squares based optimization algorithm is developed for the purpose of detecting impulses of gonadotropin-realsing hormone from measured concentration of luteinizing hormone. The parameters in the model are estimated from hormone concentration measured in human males, and simulation results from the full closed-loop system are provided.

  20. Intrinsic chirp of attosecond pulses: Single-atom model versus experiment

    SciTech Connect

    Kazamias, S.; Balcou, Ph.

    2004-06-01

    We demonstrate and evaluate the importance of an intrinsic chirp inherent to attosecond pulse creation accompanying high-order harmonic generation in recently published experimental data by Dinu et al. [Phys. Rev. Lett. 91, 063901 (2003)]. We present an analytical model, from which the atomic origin of the harmonic chirp is clearly understood. Moreover, the behavior of the chirp as a function of experimental parameters such as laser intensity is inferred. The comparison between our model and the experimental data provides us with useful information about the conditions in which the high-order harmonics is generated.

  1. Pulsed Inductive Thruster (PIT): Modeling and Validation Using the MACH2 Code

    NASA Technical Reports Server (NTRS)

    Schneider, Steven (Technical Monitor); Mikellides, Pavlos G.

    2003-01-01

    Numerical modeling of the Pulsed Inductive Thruster exercising the magnetohydrodynamics code, MACH2 aims to provide bilateral validation of the thruster's measured performance and the code's capability of capturing the pertinent physical processes. Computed impulse values for helium and argon propellants demonstrate excellent correlation to the experimental data for a range of energy levels and propellant-mass values. The effects of the vacuum tank wall and massinjection scheme were investigated to show trivial changes in the overall performance. An idealized model for these energy levels and propellants deduces that the energy expended to the internal energy modes and plasma dissipation processes is independent of the propellant type, mass, and energy level.

  2. CORONAL FUZZINESS MODELED WITH PULSE-HEATED MULTI-STRANDED LOOP SYSTEMS

    SciTech Connect

    Guarrasi, Massimiliano; Reale, Fabio; Peres, Giovanni

    2010-08-10

    Coronal active regions are observed to get increasingly fuzzy (i.e., increasingly confused and uniform) in increasingly hard energy bands or lines. We explain this as evidence of fine multi-temperature structure of coronal loops. To this end, we model bundles of loops made of thin strands, each heated by short and intense heat pulses. For simplicity, we assume that the heat pulses are all equal and triggered only once in each strand at a random time. The pulse intensity and cadence are selected so as to have steady active region loops ({approx}3 MK) on average. We compute the evolution of the confined heated plasma with a hydrodynamic loop model. We then compute the emission along each strand in several spectral lines, from cool ({<=}1 MK), to warm (2-3 MK) lines, detectable with Hinode/Extreme-ultraviolet Imaging Spectrometer, to hot X-ray lines. The strands are then put side by side to construct an active region loop bundle. We find that in the warm lines (2-3 MK) the loop emission fills all the available image surface. Therefore, the emission appears quite uniform and it is difficult to resolve the single loops, while in the cool lines the loops are considerably more contrasted and the region is less fuzzy. The main reasons for this effect are that, during their evolution, i.e., pulse heating and slow cooling, each strand spends a relatively long time at temperatures around 2-3 MK and it has a high emission measure during that phase, so the whole region appears more uniform or smudged. We predict that fuzziness should be reduced in the hot UV and X-ray lines.

  3. Pulsed photothermal deflection and diffraction effects: numerical modeling based on Fresnel diffraction theory

    NASA Astrophysics Data System (ADS)

    Han, Yue; Wu, Z. L.; Rosenshein, Joseph S.; Thomsen, Marshall; Zhao, Qiang; Moncur, Kent

    1999-12-01

    We present a comprehensive theoretical model suitable for treating the effect of pulsed collinear photothermal deflection spectroscopy (PDS). The work is an extension of the theoretical model previously developed for the mirage effect, which can take into account both photothermal deflection and photothermal diffraction effects based on the Fresnel diffraction theory. With the diffraction model, both the collinear PDS and the photothermal lensing spectroscopy techniques can be treated in a unified manner. The model provides a detailed analysis of the laser-induced optical diffraction effect and can be used to optimize experimental parameters. The modeled results are presented in detail, with an emphasis on the advantages of using a near-field detection scheme for achieving the best sensitivity to local temperature change and better experimental stability against environmental noise.

  4. Axial and diffusion models of the laser pulse propagation in a highly-scattering medium

    SciTech Connect

    Tereshchenko, Sergei A; Danilov, Arsenii A; Podgaetskii, Vitalii M; Vorob'ev, Nikolai S

    2004-06-30

    The propagation of laser radiation through a layer of a highly-scattering medium (HSM) is considered on the basis of two theoretical models: a nonstationary axial (two-flux) model and a nonstationary diffusion model. Analytic expressions for the temporal distributions of the photons of an ultrashort laser pulse transmitted through the HSM are presented. Experimental temporal distributions are used to obtain the parameters of models corresponding to an HSM, to determine the theoretical temporal distributions, and to compare them with the experimental curves. These two theoretical models are compared quantitatively for the first time. Their advantages and drawbacks that must be considered in the development of HSM transmission optical tomography are pointed out. (light scattering)

  5. Application of the Monte Carlo method for modeling passage of ultrashort laser pulses through an inhomogeneous medium with moving scatterers

    NASA Astrophysics Data System (ADS)

    Starukhin, P. Yu.; Klinaev, Yu. V.

    2011-05-01

    We present the results of numerical modeling of passage of ultrashort laser pulses through an inhomogeneous layered medium with moving scatterers, based on solution of the nonsteady-state radiation transport equation by the Monte Carlo method. We consider the effects of Doppler broadening of the backscattered radiation spectrum in biological tissues. We have analyzed the dynamics of propagation of a short laser pulse within a multilayer model of human skin. We have studied the possibilities for tomography of different layers of biological tissue based on analysis of the spectrum of the scattered radiation pulse.

  6. Self-healing slip pulses in dynamic rupture models due to velocity-dependent strength

    USGS Publications Warehouse

    Beeler, N.M.; Tullis, T.E.

    1996-01-01

    rise time and rupture propagation velocity depend on the choice of constitutive parameters. The second strength function is a natural log velocity-dependent form similar to constitutive laws that fit experimental rock friction data at lower velocities. Slip pulses also arise with this function. For a reasonable choice of constitutive parameters, slip pulses with this function do not propagate at speeds greater than the Raleighwave velocity. The calculated slip pulses are similar in many aspects to seismic observations of short rise time. In all cases of self-healing slip pulses, the residual stress increases with distance behind the trailing edge of the pulse so that the final stress drop is much less than the dynamic stress drop, in agreement with the model of Brune (1976) and some recent seismological observations of rupture.

  7. Pulsed Cl2/Ar inductively coupled plasma processing: 0D model versus experiments

    NASA Astrophysics Data System (ADS)

    Despiau-Pujo, E.; Brihoum, M.; Bodart, P.; Darnon, M.; Cunge, G.

    2014-11-01

    Comparisons between measurements and spatially-averaged (0D) simulations of low-pressure Ar and Cl2 pulsed-plasmas in an industrial inductively coupled reactor are reported. Our analysis focuses on the impact of the pulsing parameters (frequency f, duty cycle dc) on the chemical reactivity of the plasma and on the ion fluxes to the walls. Charged particle densities and ion fluxes are highly modulated when the plasma is pulsed at 1 kHz < f < 20 kHz. In rare gas Ar plasmas, the ion flux rise time is short (50 μs), therefore the dc has almost no influence on the ion flux value during the pulse. By contrast, in molecular electronegative Cl2 plasmas, both the value and rise/decay time of the ion flux during the on and off-periods depend strongly on the dc. This is because in Cl2 both the plasma chemistry and electronegativity depend on the dc. During the off-period, the electron density drops much faster than the negative ion density, leading to a large increase in plasma electronegativity. A minimum afterglow time (75 µs) is required for an ion-ion plasma to form and for the sheath to collapse, exposing the walls and wafers to a negative ion flux. The positive ion flux is 3 to 10 times smaller in Cl2 than in Ar for the same operating conditions. In contrast with charged species, the radical (Cl) kinetics are slow and thus the radical density is hardly modulated for f > 1 kHz. However, the dc strongly influences the Cl2/Cl density ratio and is an excellent knob for controlling the plasma chemical reactivity: the higher the dc the higher the Cl density. The trends and quantities in the 0D simulation are in close agreement with experiments. This proves the capacity of global models to reproduce the fundamental features of pulsed plasmas in simple chemistries and to assist the development of pulsed processes.

  8. Dynamical studies of model membrane and cellular response to nanosecond, high-intensity pulsed electric fields

    NASA Astrophysics Data System (ADS)

    Hu, Qin

    The dynamics of electroporation of biological cells subjected to nanosecond, high intensity pulses are studied based on a coupled scheme involving the current continuity and Smoluchowski equations. The improved pore formation energy model includes a dependence on pore population and density. It also allows for variable surface tension and incorporates the effects of finite conductivity on the electrostatic correction term, which was not considered by the simple energy models in the literature. It is shown that E(r) becomes self-adjusting with variations in its magnitude and profile. The whole scheme is self-consistent and dynamic. An electromechanical analysis based on thin-shell theory is presented to analyze cell shape changes in response to external electric fields. The calculations demonstrate that at large fields, the spherical cell geometry can be modified, and even ellipsoidal forms may not be appropriate to account for the resulting shape. It is shown that, in keeping with reports in the literature, the final shape depends on membrane thickness. This has direct implications for tissues in which significant molecular restructuring can occur. This study is also focused on obtaining qualitative predictions of pulse width dependence to apoptotic cell irreversibility that has been observed experimentally. The analysis couples a distributed electrical model for current flow with the Smoluchowski equation to provide self-consistent, time-dependent transmembrane voltages. The model captures the essence of the experimentally observed pulse-width dependence, and provides a possible physical picture that depends only on the electrical trigger. Different cell responses of normal and malignant (Farage) tonsillar B-cell are also compared and discussed. It is shown that subjecting a cell to an ultrashort, high-intensity electric pulse is the optimum way for reversible intracellular manipulation. Finally, a simple but physical atomistic model is presented for molecular

  9. Bubble Formation from Wall Orifice in Liquid Cross-Flow Under Low Gravity

    NASA Technical Reports Server (NTRS)

    Nahra, Henry K.; Kamotani, Y.

    2000-01-01

    Two-phase flows present a wide variety of applications for spacecraft thermal control systems design. Bubble formation and detachment is an integral part of the two phase flow science. The objective of the present work is to experimentally investigate the effects of liquid cross-flow velocity, gas flow rate, and orifice diameter on bubble formation in a wall-bubble injection configuration. Data were taken mainly under reduced gravity conditions but some data were taken in normal gravity for comparison. The reduced gravity experiment was conducted aboard the NASA DC-9 Reduced Gravity Aircraft. The results show that the process of bubble formation and detachment depends on gravity, the orifice diameter, the gas flow rate, and the liquid cross-flow velocity. The data are analyzed based on a force balance, and two different detachment mechanisms are identified. When the gas momentum is large, the bubble detaches from the injection orifice as the gas momentum overcomes the attaching effects of liquid drag and inertia. The surface tension force is much reduced because a large part of the bubble pinning edge at the orifice is lost as the bubble axis is tilted by the liquid flow. When the gas momentum is small, the force balance in the liquid flow direction is important, and the bubble detaches when the bubble axis inclination exceeds a certain angle.

  10. Direct Numerical Simulation of Turbulent Heat Transfer Behind a Rectangular Orifice

    NASA Astrophysics Data System (ADS)

    Makino, Soihiro; Iwamoto, Kaoru; Kawamura, Hiroshi

    Direct numerical simulation of turbulent heat transfer with a rectangular orifice has been performed for Reτ0(=uτ0δ⁄ν) = 300, where uτ0 is the friction velocity calculated from the mean pressure gradient imposed to drive the flow, δ the channel half width and ν the kinematic viscosity. The Prandtl number is 0.71. The ratio of slit height to channel height is assumed to be β=0.3,0.4,0.5,0.6 and 0.7. For β=0.3-0.6, the mean flow becomes asymmetric in the wall-normal direction by the Coanda effect behind the orifice. In the case of β=0.7, however, the mean flow is symmetry. The Nusselt number profiles over the bottom and top walls are different significantly for the asymmetric cases. Large-scale Kelvin-Helmholtz(K-H) vortices are generated at the orifice edges. An entrainment process is observed in the temperature field around these vortices. Subsequently, these K-H vortices become deformed and break up into disordered small-scale structures in the shear layers behind the orifice. In this scenario, the turbulent transport is promoted in the temperature field. In addition, the separation, the reattachment and also the contraction effects are discussed on the profiles of the mean temperature, the temperature variance and the turbulent heat fluxes.

  11. On the Modeling of PHELIX and Other Pulsed-Power Experiments

    NASA Astrophysics Data System (ADS)

    Rousculp, Christopher; Reass, William; Oro, David; Turchi, Peter; Holtkamp, David; Griego, Jeffery; Reinovsky, Robert

    2011-10-01

    At LANL, pulsed power hydrodynamics employs multi mega-Amp currents, over tens of microseconds, producing hundreds of kilogauss fields in a Z-pinch configuration for the study of shocks, fluids, and material physics. The new PHELIX portable pulsed power machine demonstrated for first time the efficient coupling of a high-power capacitor bank via a toroidal transformer to a central load. The whole system sits on a 200 square foot platform for use at the LANL proton radiography facility. Additionally, magnetic FCGs are employed for very high energy density experiments. Here, explosives propel metal conductors in a coaxial, helical, or disk system to produce tens of mega-Amp currents. Currents carried in the skin depth are subject to intense Lorentz forces and Joule heating. Single-fluid, resistive MHD theory with material properties of the conductors well characterizes the experiments. One and two-dimensional computational codes solve the equations of mass, momentum, field, and energy. The grids are coupled to circuit equations describing the pulsed power driver. Results of recent experiments will be compared to modeling.

  12. Analytic Model for Description of Above-Threshold Ionization by an Intense, Short Laser Pulse

    NASA Astrophysics Data System (ADS)

    Starace, Anthony F.; Frolov, M. V.; Knyazeva, D. V.; Manakov, N. L.; Geng, J.-W.; Peng, L.-Y.

    2015-05-01

    We present an analytic model for above-threshold ionization (ATI) of an atom by an intense, linearly-polarized short laser pulse. Our quantum analysis provides closed-form formulas for the differential probability of ATI, with amplitudes given by a coherent sum of partial amplitudes describing ionization by neighboring optical cycles near the peak of the intensity envelope of a short laser pulse. These analytic results explain key features of short-pulse ATI spectra, such as the left-right asymmetry in the ionized electron angular distribution, the multi-plateau structures, and both large-scale and fine-scale oscillation patterns resulting from quantum interferences of electron trajectories. The ATI spectrum in the middle part of the ATI plateau is shown to be sensitive to the spatial symmetry of the initial bound state of the active electron owing to contributions from multiple-return electron trajectories. An extension of our analytic formulas to real atoms provides results that are in good agreement with results of numerical solutions of the time-dependent Schrödinger equation for He and Ar atoms. Research supported in part by NSF Grant No. PHY-1208059, by RFBR Grant No. 13-02-00420, by Ministry of Ed. & Sci. of the Russian Fed. Proj. No. 1019, by NNSFC Grant Nos. 11322437, 11174016, and 11121091, and by the Dynasty Fdn. (MVF & DVK).

  13. Inductive pulsed plasma thruster model with time-evolution of energy and state properties

    NASA Astrophysics Data System (ADS)

    Polzin, K. A.; Sankaran, K.; Ritchie, A. G.; Reneau, J. P.

    2013-11-01

    A model for pulsed inductive plasma acceleration is presented that consists of a set of circuit equations coupled to both a one-dimensional (1D) equation of motion and an equation governing the partitioning of energy. The latter two equations are obtained for the plasma current sheet by treating it as a single element of finite volume and integrating the governing equations over that volume. The integrated terms are replaced where necessary by physically equivalent approximations that are calculated through the solution of other parts of the governing equation set. The model improves upon previous 1D performance models by permitting the time-evolution of the temperature consistent with the time-varying energy flux into the plasma. The plasma state properties are also more realistically modelled and evolved in time, allowing for the tailoring of the model to different gases that may be chosen as propellants. Computational results for argon propellant are presented to demonstrate the efficacy of the model. The model produces a result where efficiency is maximized at a given value of the electrodynamic scaling term known as the dynamic impedance parameter. The scaling of different energy sinks as a function of the dynamic impedance parameter provides insight into the global energy partitioning in these types of accelerators. Results from the present model deviate from the previous version where temperature is selected as an input without regard for the energy that would be deposited to heat the gas to that temperature. Qualitatively and quantitatively, the model predicts specific impulse values that compare favourably with those measured for two separate inductive pulsed plasma thrusters. Efficiency is underpredicted in the regime where data are available, but the trends in the data and simulations follow similar trajectories that appear to be converging towards a predicted peak efficiency as the dynamic impedance parameter is increased.

  14. One-dimensional computational model of pulse wave propagation in the human bronchial tree.

    PubMed

    Clavica, Francesco; Alastruey, Jordi; Borlotti, Alessandra; Sherwin, Spencer J; Khir, Ashraf W

    2010-01-01

    Airflow in the respiratory system has been predominantly studied in rigid ducts. Three-dimensional simulations are computationally expensive. One-dimensional (1-D) modelling offers a good compromise between accuracy and computational cost. In this work we described the propagation of air pulse in a model of human airways using the 1-D equations of flow in compliant vessels. Seven generations of bifurcations, starting from the trachea, were studied. Peripheral airways (from the 8(th) to 23(rd) generation) were modelled using lumped parameter models. Peripheral resistance values for normal and emphysematous lungs were taken from the literature. An acceleration pulse, very short in time, was enforced at the inlet of trachea. The results suggest that compression (positive pressure peaks) and expansion (negative pressure peaks) waves are generated according to the reflection coefficients of the corresponding reflection sites (bifurcations and terminal reflections). Different values for peripheral bronchial resistance generate three different terminal reflections, all negative with different wave amplitudes. The sensitivity of the code to different peripheral resistances suggests that the 1-D formulation is a promising tool for a better understanding of the impact of disease on the velocity and pressure waveforms in the first generations of airway vessels. PMID:21096163

  15. Evaluation of the transmission line model for couplant layer corrections in pulse-echo measurements.

    PubMed

    Sturtevant, Blake; Pantea, Cristian; Sinha, Dipen

    2013-05-01

    An acoustic couplant layer plays an integral role in many ultrasonic nondestructive testing and material characterization applications. It is important to account for this layer for accurate time-delay measurements. In pulse-echo measurements, the couplant layer can be accounted for by modeling the frequency dependence of phase delay. In this paper, two such models are evaluated for robustness in determining an accurate phase velocity: a simple linear relationship and the acoustic transmission line with its associated nonlinear expression. For this evaluation, measurements of acoustic phase delay in an aluminum sample were made by the pulse-echo method using tone bursts of 1800 different carrier frequencies between 35 and 125 MHz. The transmission line model was fit to the measured data using an unconstrained nonlinear least squares fitting routine with two free parameters: the acoustic phase velocity in the sample and the couplant thickness. It was found that this nonlinear model was extremely sensitive to the initial parameter guesses and could not unambiguously determine both the couplant layer thickness and acoustic phase velocity. In contrast, the faster and simpler linear least squares fit to the delay data determines a unique phase velocity in agreement with resonant ultrasound spectroscopy, an independent measurement technique. PMID:23661128

  16. Numerical modeling of laser shock peening with femtosecond laser pulses and comparisons to experiments

    NASA Astrophysics Data System (ADS)

    Wu, Benxin; Tao, Sha; Lei, Shuting

    2010-04-01

    A physics-based model has been developed for laser shock peening (LSP) with femtosecond (fs) laser pulses (fs-LSP), which has never been reported in literature to the authors' best knowledge. The model is tested by comparing simulations with measured plume/shock wave front transient propagations and the LSP-induced hardness enhancement layer thickness. Reasonably good agreements have been obtained. The model shows that fs-LSP can produce much higher pressure than LSP with nanosecond (ns) laser pulses (ns-LSP), and it can also generate very large compressive residual stress in the workpiece near-surface layer with a thickness up to ˜100 μm. The developed model provides a powerful guiding tool for the fundamental study and the practical applications of fs-LSP. This study, together with the recently reported work by Nakano et al. [Journal of Laser Micro/Nanoengineering 4(1) (2009) 35-38], has confirmed the feasibility of fs-LSP on both theoretical and experimental sides.

  17. Pulsed focused ultrasound exposures enhance locally administered gene therapy in a murine solid tumor model

    PubMed Central

    Ziadloo, Ali; Xie, Jianwu; Frenkel, Victor

    2013-01-01

    Gene therapy by intratumoral injection is a promising approach for treating solid tumors. However, this approach has limited success due to insufficient distribution of gene vectors used for gene delivery. Previous studies have shown that pulsed-focused ultrasound (pFUS) can enhance both systemic and local delivery of therapeutic agents in solid tumors and other disease models. Here, murine squamous cell carcinoma flank tumors were treated with single intratumoral injection of naked tumor necrosis factor-alpha (TNF-α) plasmid, either with or without a preceding pFUS exposure. The exposures were given at 1 MHz, at a spatial average, temporal peak intensity of 2660 W cm–2, using 50 ms pulses, given at a pulse repetition frequency of 1 Hz. One hundred pulses were given at individual raster points, spaced evenly over the projected surface of the tumor at a distance of 2 mm. Exposures alone had no effect on tumor growth. Significant growth inhibition was observed with injection of TNF-α plasmid, and tumor growth was further inhibited with pFUS. Improved results with pFUS correlated with larger necrotic regions in histological sections and improved distribution and penetration of fluorescent surrogate nanoparticles. Electron microscopy demonstrated enlarged gaps between cells in exposed tissue, and remote acoustic palpation showed decreases in tissue stiffness after pFUS. Combined, these results suggest pFUS effects may be reducing barriers for tissue transport and additionally lowering interstitial fluid pressure to further improve delivery and distribution of injected plasmid for greater therapeutic effects. This suggests that pFUS could potentially be beneficial for improving local gene therapy treatment of human malignancies. PMID:23464051

  18. An extended self-organizing map network for modeling and control of pulse jet fabric filters.

    PubMed

    Zhuang, H; Chiu, M S

    2001-07-01

    Pulse jet fabric filters (PJFFs) have become an attractive option of particulate collection utilities, because they can meet stringent particulate emission limits regardless of variation in operating conditions. Despite their wide applications, the present control algorithm for PJFFs can best be described as rudimentary. In this paper, a modeling and control strategy based on the local model network (LMN) is proposed. An extended self-organizing map (ESOM) network is developed to construct the LMN model of the filtration process using the filter's input-output data. Subsequently, these ESOM local models are incorporated into the design of local generalized predictive controllers (GPC), and the proposed controller design is obtained as the weighted sum of these local controllers. Simulation results show that the proposed controller design yields a better performance than both conventional GPC and proportional plus integral (PI) controllers yield. PMID:15658222

  19. A study of the discharge coefficient of jets from angled slots and conical orifices

    NASA Astrophysics Data System (ADS)

    Linfield, Kevin William

    2000-10-01

    Non-ideal flows through angled orifices occur often in engineering applications such as mass flow meters, blast-wave simulators, gas propulsion devices and projectile launchers. For such flows, a correction factor in the form of a discharge coefficient is required to facilitate good design and efficient operation. The discharge coefficient depends on many parameters including atmospheric to stagnation pressure ratio, gas specific heat ratio, exit to channel area ratio, orifice shape, wall angle and orifice edge rounding. The dependence on these parameters (except edge rounding) was studied numerically by developing a two-dimensional finite-difference computer program that solves the subsonic flowfield in the hodograph plane by a relaxation method and the attached supersonic flowfield, if present, in the physical plane by a method of characteristics, joined together at the sonic surface by matching stream function values. The discharge coefficient was also studied experimentally by developing and testing an experimental facility using a new technique based on the partial blowdown of a pressurized vessel through a short pipe ending with conical orifices of different area ratios, wall angles and orifice edge roundings. Numerical and experimental data from these studies and also from the literature are compared and discussed. A software package called the " Cd Algorithm" was developed to reproduce quickly the combined numerical and experimental discharge coefficients for the entire set of parameters, and it outperforms previous algorithms in accuracy, efficiency and comprehensiveness. This Cd Algorithm uses analytical, numerical and experimental results at the limits for incompressible, critical and choked flows, and other Cd values between these limits are reproduced by using piecewise cubic polynomial splines.

  20. On the propagation mechanism of a detonation wave in a round tube with orifice plates

    NASA Astrophysics Data System (ADS)

    Ciccarelli, G.; Cross, M.

    2016-06-01

    This study deals with the investigation of the detonation propagation mechanism in a circular tube with orifice plates. Experiments were performed with hydrogen air in a 10-cm-inner-diameter tube with the second half of the tube filled with equally spaced orifice plates. A self-sustained Chapman-Jouguet (CJ) detonation wave was initiated in the smooth first half of the tube and transmitted into the orifice-plate-laden second half of the tube. The details of the propagation were obtained using the soot-foil technique. Two types of foils were used between obstacles, a wall-foil placed on the tube wall, and a flat-foil (sooted on both sides) placed horizontally across the diameter of the tube. When placed after the first orifice plate, the flat foil shows symmetric detonation wave diffraction and failure, while the wall foil shows re-initiation via multiple local hot spots created when the decoupled shock wave interacts with the tube wall. At the end of the tube, where the detonation propagated at an average velocity much lower than the theoretical CJ value, the detonation propagation is much more asymmetric with only a few hot spots on the tube wall leading to local detonation initiation. Consecutive foils also show that the detonation structure changes after each obstacle interaction. For a mixture near the detonation propagation limit, detonation re-initiation occurs at a single wall hot spot producing a patch of small detonation cells. The local overdriven detonation wave is short lived, but is sufficient to keep the global explosion front propagating. Results associated with the effect of orifice plate blockage and spacing on the detonation propagation mechanism are also presented.

  1. Exploration of the retroperitoneum using the transvaginal natural orifice transluminal endoscopic surgery technique.

    PubMed

    Zacharopoulou, Chrysoula; Nassif, Joseph; Allemann, Pierre; Dallemagne, Bernard; Perretta, Silvana; Marescaux, Jacques; Wattiez, Arnaud

    2009-01-01

    We sought to evaluate the feasibility of the retroperitoneum's exploration via natural orifice transluminal endoscopic surgery (NOTES) using transvaginal access in a porcine model, and its possible application in human beings. Six female pigs (25-30 kg) were used to establish anatomic landmarks and technical steps. Six additional pigs were used for the survival study. Under general anesthesia and with the pig supine, a 1-cm posterolateral colpotomy was performed with the double-channel gastroscope's needle knife. The incision was enlarged laterally using blunt dissection while keeping in contact with the psoas muscle. A retroperitoneal tunnel was created using carbon-dioxide dissection and the movements of the gastroscope up to the level of the kidney. The colpotomy site was closed using interrupted sutures (polyglactin 2/0). A follow-up laparoscopy and necropsy were performed 3 weeks postoperatively. Successful access to the retroperitoneum was achieved in all pigs with a mean operative time of 30 minutes. However, in the first 3 pigs used for the acute study, the peritoneum was perforated during the six-pig dissection and the procedure was abandoned because of the space's collapse. No perforation occurred during the survival study. An excellent view of the retroperitoneal space and structures, such as the vascular and lymphatic tissues, the kidney, the adrenal gland, and the ureter, was obtained. No intraoperative complications or bleeding or injury to any of the retroperitoneal structures occurred. The 3-week follow-up laparoscopy showed no adhesions or abscesses. These findings were confirmed at necropsy. The retroperitoneal space can be successfully accessed via NOTES. Transvaginal NOTES access to the retroperitoneum avoids any transparietal trocars, so it could decrease surgical trauma, be better tolerated, and offer better visualization, with the obvious gender limitation. Future clinical application in human beings may include procedures such as

  2. Observations and Modeling of the Pulse-driven Cool Plasma Ejecta in the Solar Atmosphere

    NASA Astrophysics Data System (ADS)

    Srivastava, Abhishek K.; Murawski, . Kris; Kayshap, Pradeep

    2012-07-01

    The cool plasma ejecta are ubiquitous in the solar atmosphere, and have significant implications on its mass and energy transport. We present two case studies of the SDO/AIA observations of (i) cool jet at north polar region, and (ii) the cool surge ejecta at the active region boundary. The common nature between these two different class of plasma dynamics is that both do not reveal any signature of strong heating during course of their life-times. The surge shows some evidence of heating at its footpoint, however, mostly not visible in the SDO/AIA filters sensitive to the higher coronal temperatures. Similarly, the polar jet is also only evident in the SDO/AIA 304 Å channel that is sensitive to the plasma maintained around 0.1 MK, and does not show any signature of heating. We model these cool jets by launching reconnection generated pulses in the VAL-III C model of the solar temperature as an initial condition. For the case of cool polar jet, we launch reconnection generated velocity pulse in the more realistic solar atmosphere, which steepens into a shock at higher altitudes and triggers plasma perturbations exhibiting the observed features of the jet. However, the footpoint of the surge shows small heating episode in the second case study, therefore, we consider the excitation of reconnection generated thermal pulse which triggers plasma perturbations approximately exhibiting the observed features of the surge, e.g., average velocity, height, width, life-time, and fine structures at its base. We also compare our new results with the existing models and observations of such jets, and plasma flows especially reported in the SDO era.

  3. New insights on the propagation of pulsed atmospheric plasma streams: From single jet to multi jet arrays

    SciTech Connect

    Robert, E.; Darny, T.; Dozias, S.; Iseni, S.; Pouvesle, J. M.

    2015-12-15

    Atmospheric pressure plasma propagation inside long dielectric tubes is analyzed for the first time through nonintrusive and nonperturbative time resolved bi-directional electric field (EF) measurements. This study unveils that plasma propagation occurs in a region where longitudinal EF exists ahead the ionization front position usually revealed from plasma emission with ICCD measurement. The ionization front propagation induces the sudden rise of a radial EF component. Both of these EF components have an amplitude of several kV/cm for helium or neon plasmas and are preserved almost constant along a few tens of cm inside a capillary. All these experimental measurements are in excellent agreement with previous model calculations. The key roles of the voltage pulse polarity and of the target nature on the helium flow patterns when plasma jet is emerging in ambient air are documented from Schlieren visualization. The second part of this work is then dedicated to the development of multi jet systems, using two different setups, based on a single plasma source. Plasma splitting in dielectric tubes drilled with sub millimetric orifices, but also plasma transfer across metallic tubes equipped with such orifices are reported and analyzed from ICCD imaging and time resolved EF measurements. This allows for the design and the feasibility validation of plasma jet arrays but also emphasizes the necessity to account for voltage pulse polarity, target potential status, consecutive helium flow modulation, and electrostatic influence between the produced secondary jets.

  4. New insights on the propagation of pulsed atmospheric plasma streams: From single jet to multi jet arrays

    NASA Astrophysics Data System (ADS)

    Robert, E.; Darny, T.; Dozias, S.; Iseni, S.; Pouvesle, J. M.

    2015-12-01

    Atmospheric pressure plasma propagation inside long dielectric tubes is analyzed for the first time through nonintrusive and nonperturbative time resolved bi-directional electric field (EF) measurements. This study unveils that plasma propagation occurs in a region where longitudinal EF exists ahead the ionization front position usually revealed from plasma emission with ICCD measurement. The ionization front propagation induces the sudden rise of a radial EF component. Both of these EF components have an amplitude of several kV/cm for helium or neon plasmas and are preserved almost constant along a few tens of cm inside a capillary. All these experimental measurements are in excellent agreement with previous model calculations. The key roles of the voltage pulse polarity and of the target nature on the helium flow patterns when plasma jet is emerging in ambient air are documented from Schlieren visualization. The second part of this work is then dedicated to the development of multi jet systems, using two different setups, based on a single plasma source. Plasma splitting in dielectric tubes drilled with sub millimetric orifices, but also plasma transfer across metallic tubes equipped with such orifices are reported and analyzed from ICCD imaging and time resolved EF measurements. This allows for the design and the feasibility validation of plasma jet arrays but also emphasizes the necessity to account for voltage pulse polarity, target potential status, consecutive helium flow modulation, and electrostatic influence between the produced secondary jets.

  5. Analytical modeling of laser pulse heating of embedded biological targets: An application to cutaneous vascular lesions

    NASA Astrophysics Data System (ADS)

    Mirkov, Mirko; Sherr, Evan A.; Sierra, Rafael A.; Lloyd, Jenifer R.; Tanghetti, Emil

    2006-06-01

    Detailed understanding of the thermal processes in biological targets undergoing laser irradiation continues to be a challenging problem. For example, the contemporary pulsed dye laser (PDL) delivers a complex pulse format which presents specific challenges for theoretical understanding and further development. Numerical methods allow for adequate description of the thermal processes, but are lacking for clarifying the effects of the laser parameters. The purpose of this work is to derive a simplified analytical model that can guide the development of future laser designs. A mathematical model of heating and cooling processes in tissue is developed. Exact analytical solutions of the model are found when applied to specific temporal and spatial profiles of heat sources. Solutions are reduced to simple algebraic expressions. An algorithm is presented for approximating realistic cases of laser heating of skin structures by heat sources of the type found to have exact solutions. The simple algebraic expressions are used to provide insight into realistic laser irradiation cases. The model is compared with experiments on purpura threshold radiant exposure for PDL. These include data from four independent groups over a period of 20 years. Two of the data sets are taken from previously published articles. Two more data sets were collected from two groups of patients that were treated with two PDLs (585 and 595 nm) on normal buttocks skin. Laser pulse durations were varied between 0.5 and 40 ms radiant exposures were varied between 3 and 20 J/cm2. Treatment sites were evaluated 0.5, 1, and 24 hours later to determine purpuric threshold. The analytical model is in excellent agreement with a wide range of experimental data for purpura threshold radiant exposure. The data collected by independent research groups over the last 20 years with PDLs with wavelengths ranged from 577 to 595 nm were described accurately by this model. The simple analytical model provides an accurate

  6. Envelope Model Simulation of Laser Wakefield Acceleration with Realistic Laser Pulses from the Texas Petawatt

    NASA Astrophysics Data System (ADS)

    Weichman, Kathleen; Higuera, Adam; Abell, Dan; Cowan, Ben; Fazel, Neil; Cary, John; Downer, Michael

    2015-11-01

    In a laser wakefield accelerator (LWFA), diffraction of an over-focused laser pulse can provide localized electron injection, leading to the production of a monoenergetic electron bunch. While electron energies up to several GeV have been reported at the Texas Petawatt Laser facility, near-Gaussian beam simulations predict energies higher than have been observed. Experimentally measured laser profiles are non-Gaussian, indicating that closer agreement with experimental conditions is needed to predictively model this experiment. The implementation of the envelope model in the particle-in-cell code VORPAL lowers the computational cost of capturing injection dynamics during the early evolution of laser wakefields. We compare VORPAL envelope model simulations using laser pulses based on experimentally measured profiles versus a corresponding a two-Gaussian approximation. We acknowledge DOE Grants No. DE-SC0011617 and DE-SC0012444, DOE/NSF Grant No. DE-SC0012584, and the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. KW is supported by the DOE CSGF under Grant No. DE-FG02-97ER25308.

  7. MATLAB/Simulink Pulse-Echo Ultrasound System Simulator Based on Experimentally Validated Models.

    PubMed

    Kim, Taehoon; Shin, Sangmin; Lee, Hyongmin; Lee, Hyunsook; Kim, Heewon; Shin, Eunhee; Kim, Suhwan

    2016-02-01

    A flexible clinical ultrasound system must operate with different transducers, which have characteristic impulse responses and widely varying impedances. The impulse response determines the shape of the high-voltage pulse that is transmitted and the specifications of the front-end electronics that receive the echo; the impedance determines the specification of the matching network through which the transducer is connected. System-level optimization of these subsystems requires accurate modeling of pulse-echo (two-way) response, which in turn demands a unified simulation of the ultrasonics and electronics. In this paper, this is realized by combining MATLAB/Simulink models of the high-voltage transmitter, the transmission interface, the acoustic subsystem which includes wave propagation and reflection, the receiving interface, and the front-end receiver. To demonstrate the effectiveness of our simulator, the models are experimentally validated by comparing the simulation results with the measured data from a commercial ultrasound system. This simulator could be used to quickly provide system-level feedback for an optimized tuning of electronic design parameters. PMID:26685232

  8. A Three-Pulse Release Tablet for Amoxicillin: Preparation, Pharmacokinetic Study and Physiologically Based Pharmacokinetic Modeling

    PubMed Central

    Li, Jin; Chai, Hongyu; Li, Yang; Chai, Xuyu; Zhao, Yan; Zhao, Yunfan; Tao, Tao; Xiang, Xiaoqiang

    2016-01-01

    Background Amoxicillin is a commonly used antibiotic which has a short half-life in human. The frequent administration of amoxicillin is often required to keep the plasma drug level in an effective range. The short dosing interval of amoxicillin could also cause some side effects and drug resistance, and impair its therapeutic efficacy and patients’ compliance. Therefore, a three-pulse release tablet of amoxicillin is desired to generate sustained release in vivo, and thus to avoid the above mentioned disadvantages. Methods The pulsatile release tablet consists of three pulsatile components: one immediate-release granule and two delayed release pellets, all containing amoxicillin. The preparation of a pulsatile release tablet of amoxicillin mainly includes wet granulation craft, extrusion/spheronization craft, pellet coating craft, mixing craft, tablet compression craft and film coating craft. Box–Behnken design, Scanning Electron Microscope and in vitro drug release test were used to help the optimization of formulations. A crossover pharmacokinetic study was performed to compare the pharmacokinetic profile of our in-house pulsatile tablet with that of commercial immediate release tablet. The pharmacokinetic profile of this pulse formulation was simulated by physiologically based pharmacokinetic (PBPK) model with the help of Simcyp®. Results and Discussion Single factor experiments identify four important factors of the formulation, namely, coating weight of Eudragit L30 D-55 (X1), coating weight of AQOAT AS-HF (X2), the extrusion screen aperture (X3) and compression forces (X4). The interrelations of the four factors were uncovered by a Box–Behnken design to help to determine the optimal formulation. The immediate-release granule, two delayed release pellets, together with other excipients, namely, Avicel PH 102, colloidal silicon dioxide, polyplasdone and magnesium stearate were mixed, and compressed into tablets, which was subsequently coated with Opadry

  9. Semianalytic theory of self-similar optical propagation and mode locking using a shape-adaptive model pulse

    SciTech Connect

    Jirauschek, Christian; Ilday, F. Oemer

    2011-06-15

    A semianalytic theory for the pulse dynamics in similariton amplifiers and lasers is presented, based on a model pulse with adaptive shape. By changing a single parameter, this test function can be continuously tweaked between a pure Gaussian and a pure parabolic profile and can even represent sech-like pulses, the shape of a soliton. This approach allows us to describe the pulse evolution in the self-similar and other regimes of optical propagation. Employing the method of moments, the evolution equations for the characteristic pulse parameters are derived from the governing nonlinear Schroedinger or Ginzburg-Landau equation. Due to its greatly reduced complexity, this description allows for extensive parameter optimization, and can aid intuitive understanding of the dynamics. As an application of this approach, we model a soliton-similariton laser and validate the results against numerical simulations. This constitutes a semianalytic model of the soliton-similariton laser. Due to the versatility of the model pulse, it can also prove useful in other application areas.

  10. Oscillatory Pattern Generation of the Olfactory Center Using Pulse-Type Hardware Chaotic Neuron Models

    NASA Astrophysics Data System (ADS)

    Saito, Ken; Hatano, Hirokazu; Saito, Minoru; Sekine, Yoshifumi

    Oscillatory patterns of electrical activity are a ubiquitous feature in nervous systems. Oscillatory patterns play an important role in the processing of sensory information pattern recognition. For example, earlier reports describe that the oscillatory patterns in the olfactory center of the land slug are changed by odor stimuli to the tentacles. Olfactory processing has also been studied in relation to rabbits and land slugs through the construction and use of mathematical neural network models. However, a large-scale model is necessary for the study of a model which has sensory information recognition by the oscillatory pattern. Therefore, the construction of a hardware model that can generate oscillatory patterns is desired because nonlinear operations can be processed at higher speeds than the mathematical model. We are studying about the neural network using hardware neuron models to construct the olfactory center model of the living organisms. In the present study, we discuss about the oscillatory pattern generation of the olfactory center using pulse-type hardware chaotic neuron models. Our model shows periodic, quasi-periodic and chaotic oscillations such as the olfactory center of living organisms by changing the synaptic connection weights.

  11. Experimental validation of a linear model for data reduction in chirp-pulse microwave CT.

    PubMed

    Miyakawa, M; Orikasa, K; Bertero, M; Boccacci, P; Conte, F; Piana, M

    2002-04-01

    Chirp-pulse microwave computerized tomography (CP-MCT) is an imaging modality developed at the Department of Biocybernetics, University of Niigata (Niigata, Japan), which intends to reduce the microwave-tomography problem to an X-ray-like situation. We have recently shown that data acquisition in CP-MCT can be described in terms of a linear model derived from scattering theory. In this paper, we validate this model by showing that the theoretically computed response function is in good agreement with the one obtained from a regularized multiple deconvolution of three data sets measured with the prototype of CP-MCT. Furthermore, the reliability of the model as far as image restoration in concerned, is tested in the case of space-invariant conditions by considering the reconstruction of simple on-axis cylindrical phantoms. PMID:12022626

  12. Model of accelerating voltage pulse in DARHT-2 including Metglas saturation

    NASA Astrophysics Data System (ADS)

    Genoni, Thomas; Hughes, Thomas; Thoma, Carsten

    2003-10-01

    The DARHT-2 facility (Los Alamos National Laboratory) accelerates a 2 microsecond electron beam using a series of inductive accelerating cells. The cell inductance is provided by large Metglas cores, which are driven by a pulse-forming network (PFN). We have developed a model for this circuit which includes the nonlinear and spatially varying behavior of the Metglas. Data from experiments in which a capacitor was discharged through a Metglas core are used to develop a hysteresis model, based on the Hodgdon [Ref.1] theory of ferromagnetic materials. The resulting model is used in calculations of the output of the DARHT PFN, and comparison is made to experiments in which the PFN was terminated in a dummy resistive load. 1. M. L. Hodgdon, "Mathematical Theory and Calculations of Magnetic Hysteresis Curves", IEEE Trans. Magn., v. MAG-24, n. 6, pp. 3120-2, Nov. 1988.

  13. Modelling material dependent parameters of layer type straight coils for fast transient pulses

    NASA Astrophysics Data System (ADS)

    Tamus, Z. A.; Orosz, T.; Kiss, G. M.

    2015-10-01

    The behavior of coils in case of fast transient pulses is different from that they show at low frequencies. If the dimensions of the coil, i.e. mainly the length of the winding is much shorter than the wavelength of the signal on the coil, a lumped element model can be effectively used taking the capacitances of windings into consideration. In this study a different type of straight, layered coil have been investigated in order to determine parameters of a lumped circuit model of the windings. The frequency dependent parameters are modeled by analytical and finite element calculations and the results are compared to the results of measurements on coils. The finite element method can improve the accuracy of parameter estimation.

  14. Renal function and structure in a rat model of arterial calcification and increased pulse pressure.

    PubMed

    Gaillard, Virginie; Jover, Bernard; Casellas, Daniel; Cordaillat, Magali; Atkinson, Jeffrey; Lartaud, Isabelle

    2008-10-01

    Clinical studies suggest a strong link between tissue calcification and pressure hyperpulsatility in end stage renal disease patients. Using a Wistar rat model of arterial elastocalcinosis and hyperpulsatility [vitamin D and nicotine (VDN) treatment], we evaluated the relative importance of tissue calcification and hyperpulsatility in the etiology of renal failure. VDN rats showed significant increases in aortic wall calcium content (50 times; 992+/-171 vs. control 19+/-1 micromol/g dry wt) and pulse pressure (1.5 times; 61+/-4 vs. control 40+/-2 mmHg). Significant renal calcification (16 times; 124+/-27 vs. control 8.1+/-0.7 micromol/g dry wt) occurred mainly within the media of the preglomerular vasculature and in the areas of interstitial fibrosis in VDN. Extensive renal damages (5 times; 26+/-5% of collapsed-atrophic or sclerotic glomeruli, or glomerular cysts vs. control 5.2+/-0.3%; 28 times; 61+/-12% areas of focal, cortical areas exhibiting interstitial fibrosis per section vs. control 2.2+/-0.6%) were observed histologically. The glomerular filtration rate significantly decreased (880+/-40 vs. control 1,058+/-44 microl.min(-1).g kidney wt(-1)). Albuminuria increased six times (1.6+/-0.4 vs. control 0.27+/-0.04 mg/24 h). There were significant linear relationships between albuminuria and pulse pressure (r2=0.408; n=24) or renal calcium content (r2=0.328; n=24; P<0.05) and between glomerular filtration rate and pulse pressure (r2=0.168; n=27). To our knowledge, this study provides the first evidence of links between both 1) hyperpulsatility and renal dysfunction, and 2) renal calcification and renal dysfunction. Given the increasing frequency of end-stage renal disease, this model could prove useful for preclinical evaluation of drugs that prevent or attenuate hyperpulsatility and/or tissue calcification. PMID:18715942

  15. Modeling and optimization of single-pass laser amplifiers for high-repetition-rate laser pulses

    SciTech Connect

    Ozawa, Akira; Udem, Thomas; Zeitner, Uwe D.; Haensch, Theodor W.; Hommelhoff, Peter

    2010-09-15

    We propose a model for a continuously pumped single-pass amplifier for continuous and pulsed laser beams. The model takes into account Gaussian shape and focusing geometry of pump and seed beam. As the full-wave simulation is complex we have developed a largely simplified numerical method that can be applied to rotationally symmetric geometries. With the tapered-shell model we treat (focused) propagation and amplification of an initially Gaussian beam in a gain crystal. The implementation can be done with a few lines of code that are given in this paper. With this code, a numerical parameter optimization is straightforward and example results are shown. We compare the results of our simple model with those of a full-wave simulation and show that they agree well. A comparison of model and experimental data also shows good agreement. We investigate in detail different regimes of amplification, namely the unsaturated, the fully saturated, and the intermediate regime. Because the amplification process is affected by spatially varying saturation and exhibits a nonlinear response against pump and seed power, no analytical expression for the expected output is available. For modeling of the amplification we employ a four-level system and show that if the fluorescence lifetime of the gain medium is larger than the inverse repetition rate of the seed beam, continuous-wave amplification can be employed to describe the amplification process of ultrashort pulse trains. We limit ourselves to this regime, which implies that if titanium:sapphire is chosen as gain medium the laser repetition rate has to be larger than a few megahertz. We show detailed simulation results for titanium:sapphire for a large parameter set.

  16. Mixing of Multiple Jets with a Confined Subsonic Crossflow. Part 2; Opposed Rows of Orifices in Rectangular Ducts

    NASA Technical Reports Server (NTRS)

    Holdeman, J. D.; Liscinsky, D. S.; Bain, D. B.

    1999-01-01

    This paper summarizes experimental and computational results on the mixing of opposed rows of jets with a confined subsonic crossflow in rectangular ducts. The studies from which these results were excerpted investigated flow and geometric variations typical of the complex three-dimensional flowfield in the combustion chambers in gas turbine engines. The principal observation was that the momentum-flux ratio, J, and the orifice spacing, S/H, were the most significant flow and geometric variables. Jet penetration was critical, and penetration decreased as either momentum-flux ratio or orifice spacing decreased. It also appeared that jet penetration remained similar with variations in orifice size, shape, spacing, and momentum-flux ratio when the orifice spacing was inversely proportional to the square-root of the momentum-flux ratio. It was also seen that planar averages must be considered in context with the distributions. Note also that the mass-flow ratios and the orifices investigated were often very large (jet-to-mainstream mass-flow ratio > 1 and the ratio of orifices-area-to-mainstream- cross-sectional-area up to 0.5, respectively), and the axial planes of interest were often just downstream of the orifice trailing edge. Three-dimensional flow was a key part of efficient mixing and was observed for all configurations.

  17. Penetration of Air Jets Issuing from Circular, Square, and Elliptical Orifices Directed Perpendicularly to an Air Stream

    NASA Technical Reports Server (NTRS)

    Ruggeri, Robert S.; Callaghan, Edmund E.; Bowden, Dean T.

    1950-01-01

    An experimental investigation was conducted to determine the penetration of air jets d.irected perpendicularlY to an air stream. Jets Issuing from circular, square, and. elliptical orifices were investigated. and. the jet penetration at a position downstream of the orifice was determined- as a function of jet density, jet velocity, air-stream d.enaity, air-stream velocity, effective jet diameter, and. orifice flow coeffIcient. The jet penetrations were determined for nearly constant values of air-stream density at three tunnel-air velocities arid for a large range of Jet velocities and. densities. The results were correlated in terms of dimensionless parameters and the penetrations of the various shapes were compared. Greater penetration was obtained. with the square orifices and the elliptical orifices having an axis ratio of 4:1 at low tunnel-air velocities and low jet pressures than for the other orifices investigated. The square orifices gave the best penetrations at the higher values of tunnel-air velocity and jet total pressure.

  18. Modeling the dynamics of one laser pulse surface nanofoaming of biopolymers

    NASA Astrophysics Data System (ADS)

    Lazare, S.; Bonneau, R.; Gaspard, S.; Oujja, M.; de Nalda, R.; Castillejo, M.; Sionkowska, A.

    2009-03-01

    Self standing films of biopolymers like gelatine, collagen, and chitosan irradiated with single nanosecond or femtosecond laser pulse easily yield on their surface, a nanofoam layer, formed by a cavitation and bubble growth mechanism. The laser foams have interesting properties that challenge the molecular features of the natural extracellular matrix and which make them good candidates for fabrication of artificial matrix (having nanoscopic fibers, large availability of cell adhesion sites, permeability to fluids due to the open cell structure). As part of the mechanistic study, the dynamics of the process has been measured in the nanosecond timescale by recording the optical transmission of the films at 632.8 nm during and after the foaming laser pulse. A rapid drop 100→0% taking place within the first 100 ns supports the cavitation mechanism as described by the previous negative pressure wave model. As modeled a strong pressure rise (˜several thousands of bar) first takes place in the absorption volume due to pressure confinement and finite sound velocity, and then upon relaxation after some delay equal to the pressure transit time gives rise to a rarefaction wave (negative pressure) in which nucleation and bubble growth are very fast.

  19. The removal of Direct Orange 39 by pulsed corona discharge from model wastewater.

    PubMed

    Vujevic, D; Koprivanac, N; Bozic, A Loncaric; Locke, B R

    2004-07-01

    Untreated wastewater from the dye industry and dyehouses cannot be directly discharged into the environment due to the high content of organic matter and intensive colouration, even with low concentrations of dye. In this paper, the application of a high voltage pulsed electrical discharge in the aqueous phase has been assessed for the dye degradation. Experiments were conducted in a batch reactor using model wastewater of the commercial water-soluble monoazo dye C.I. Direct Orange 39 (DO39). The effects of zeolite and ferrous sulphate in combination with the corona discharge were examined. Experiments were conducted for a range of process parameters including pH, conductivity, type and amount of zeolite, and ferrous sulphate concentration. A mathematical model to describe the kinetics of DO39 degradation in the corona reactor was developed. Aqueous phase pulsed streamer corona discharge as a method for coloured wastewater treatment showed very high effectiveness in the case of iron salt addition (Fenton's reaction). Low pH enhanced dye removal by corona in the absence of zeolite, thus implying that the acid properties of zeolites are important in dye degradation. Ecological parameters such as COD, TC, IC, TOC and IC50 measured before and after corona treatment showed that the treated wastewater can be discharged into the environment or reused as process water. PMID:15346860

  20. Multiple attractors in stage-structured population models with birth pulses.

    PubMed

    Tang, Sanyi; Chen, Lansun

    2003-05-01

    In most models of population dynamics, increases in population due to birth are assumed to be time-independent, but many species reproduce only during a single period of the year. A single species stage-structured model with density-dependent maturation rate and birth pulse is formulated. Using the discrete dynamical system determined by its Poincaré map, we report a detailed study of the various dynamics, including (a) existence and stability of nonnegative equilibria, (b) nonunique dynamics, meaning that several attractors coexist, (c) basins of attraction (defined as the set of the initial conditions leading to a certain type of attractor), (d) supertransients, and (e) chaotic attractors. The occurrence of these complex dynamic behaviour is related to the fact that minor changes in parameter or initial values can strikingly change the dynamic behaviours of system. Further, it is shown that periodic birth pulse, in effect, provides a natural period or cyclicity that allows multiple oscillatory solutions in the continuous dynamical systems. PMID:12749535

  1. Thermal and damage data from multiple microsecond pulse trains at 532nm in an in vitro retinal model

    NASA Astrophysics Data System (ADS)

    Denton, Michael L.; Tijerina, Amanda J.; Hoffman, Aaron; Clark, Clifton D.; Noojin, Gary D.; Rickman, John M.; Castellanos, Cherry C.; Shingledecker, Aurora D.; Boukhris, Sarah J.; Thomas, Robert J.; Rockwell, Benjamin A.

    2014-03-01

    An artificially pigmented retinal pigment epithelial (RPE) cell model was used to study the damage rates for exposure to 1, 10, 100, and 1,000 230-μs laser pulses at 532 nm, at two different concentrations of melanosome particles (MPs) per cell. Multiple pulses were delivered at pulse repetition rates of 50 and 99 pulses per second. Standard fluorescence viability indicator dyes and the method of microthermography were used to assess damage and thermal responses, respectively. Although frame rate during microthermography was more than five times slower than the duration of laser pulses, thermal information was useful in refining the BTEC computational model for simulating high-resolution thermal responses by the pigmented cells. When we temporally sampled the thermal model output at a rate similar to our microthermography, the resulting thermal profiles for multiple pulses resembled the thermal experimental profiles. Complementary to the thermal simulations, our computer-generated thresholds were in good agreement with the in vitro data. Findings are examined within the context of common exposure limit definitions in the national and international laser safety standards.

  2. On the formation of vortex pairs near orifices

    NASA Astrophysics Data System (ADS)

    Blondeaux, P.; de Bernardinis, B.

    1983-10-01

    It is pointed out that a two-dimensional vortex pair is commonly generated by pushing fluid down a semiinfinite channel by means of an impulsively started piston. Sheffield (1977) calculated the trajecotories of an ideal vortex pair near channel openings of different shapes. The present investigation is concerned with a point-vortex model of the process of pair formation and a general extension of Sheffield's results. The assumption is made that viscous effects are significant only during the separation process and have negligible influence on the overall flow. In the limit of infinite Reynolds number, the problem becomes one of inviscid flow. The growing vortex sheets shed from the edge are represented by a simplified model reported by Brown and Michael (1954). The model is utilized to study the trajectories of two free vortices released symmetrically near the channel wall far from the opening of a semiinfinite channel when growing secondary vortices are present.

  3. Evaluating the use of a continuous approximation for model-based quantification of pulsed chemical exchange saturation transfer (CEST)

    PubMed Central

    Tee, Y.K.; Khrapitchev, A.A.; Sibson, N.R.; Payne, S.J.; Chappell, M.A.

    2012-01-01

    Many potential clinical applications of chemical exchange saturation transfer (CEST) have been studied in recent years. However, due to various limitations such as specific absorption rate guidelines and scanner hardware constraints, most of the proposed applications have yet to be translated into routine diagnostic tools. Currently, pulsed CEST which uses multiple short pulses to perform the saturation is the only viable irradiation scheme for clinical translation. However, performing quantitative model-based analysis on pulsed CEST is time consuming because it is necessary to account for the time dependent amplitude of the saturation pulses. As a result, pulsed CEST is generally treated as continuous CEST by finding its equivalent average field or power. Nevertheless, theoretical analysis and simulations reveal that the resulting magnetization is different when the different irradiation schemes are applied. In this study, the quantification of important model parameters such as the amine proton exchange rate from a pulsed CEST experiment using quantitative model-based analyses were examined. Two model-based approaches were considered – discretized and continuous approximation to the time dependent RF irradiation pulses. The results showed that the discretized method was able to fit the experimental data substantially better than its continuous counterpart, but the smaller fitted error of the former did not translate to significantly better fit for the important model parameters. For quantification of the endogenous CEST effect, such as in amide proton transfer imaging, a model-based approach using the average power equivalent saturation can thus be used in place of the discretized approximation. PMID:22858666

  4. Incorporation of an Energy Equation into a Pulsed Inductive Thruster Performance Model

    NASA Technical Reports Server (NTRS)

    Polzin, Kurt A.; Reneau, Jarred P.; Sankaran, Kameshwaran

    2011-01-01

    A model for pulsed inductive plasma acceleration containing an energy equation to account for the various sources and sinks in such devices is presented. The model consists of a set of circuit equations coupled to an equation of motion and energy equation for the plasma. The latter two equations are obtained for the plasma current sheet by treating it as a one-element finite volume, integrating the equations over that volume, and then matching known terms or quantities already calculated in the model to the resulting current sheet-averaged terms in the equations. Calculations showing the time-evolution of the various sources and sinks in the system are presented to demonstrate the efficacy of the model, with two separate resistivity models employed to show an example of how the plasma transport properties can affect the calculation. While neither resistivity model is fully accurate, the demonstration shows that it is possible within this modeling framework to time-accurately update various plasma parameters.

  5. Development of Unsteady Aerodynamic State-Space Models from CFD-Based Pulse Responses

    NASA Technical Reports Server (NTRS)

    Silva, Walter A.; Raveh, Daniella E.

    2001-01-01

    A method for computing discrete-time state-space models of linearized unsteady aerodynamic behavior directly from aeroelastic CFD codes is presented. The method involves the treatment of CFD-based pulse responses as Markov parameters for use in a system identification /realization algorithm. Results are presented for the AGARD 445.6 Aeroelastic Wing with four aeroelastic modes at a Mach number of 0.96 using the EZNSS Euler/Navier-Stokes flow solver with aeroelastic capability. The System/Observer/Controller Identification Toolbox (SOCIT) algorithm, based on the Ho-Kalman realization algorithm, is used to generate 15th- and 32nd-order discrete-time state-space models of the unsteady aerodynamic response of the wing over the entire frequency range of interest.

  6. Jitter model and signal processing techniques for pulse width modulation optical recording

    NASA Technical Reports Server (NTRS)

    Liu, Max M.-K.

    1991-01-01

    A jitter model and signal processing techniques are discussed for data recovery in Pulse Width Modulation (PWM) optical recording. In PWM, information is stored through modulating sizes of sequential marks alternating in magnetic polarization or in material structure. Jitter, defined as the deviation from the original mark size in the time domain, will result in error detection if it is excessively large. A new approach is taken in data recovery by first using a high speed counter clock to convert time marks to amplitude marks, and signal processing techniques are used to minimize jitter according to the jitter model. The signal processing techniques include motor speed and intersymbol interference equalization, differential and additive detection, and differential and additive modulation.

  7. Neural Network Modeling of Weld Pool Shape in Pulsed-Laser Aluminum Welds

    SciTech Connect

    Iskander, Y.S.; Oblow, E.M.; Vitek, J.M.

    1998-11-16

    A neural network model was developed to predict the weld pool shape for pulsed-laser aluminum welds. Several different network architectures were examined and the optimum architecture was identified. The neural network was then trained and, in spite of the small size of the training data set, the network accurately predicted the weld pool shape profiles. The neural network output was in the form of four weld pool shape parameters (depth, width, half-width, and area) and these were converted into predicted weld pool profiles with the use of the actual experimental poo1 profiles as templates. It was also shown that the neural network model could reliably predict the change from conduction-mode type shapes to keyhole-mode shapes.

  8. Ignition and Growth Modeling of Short Pulse Duration Shock Initiation Experiments on HNS IV

    NASA Astrophysics Data System (ADS)

    Tarver, Craig; Chidester, Steven

    2013-06-01

    Short pulse duration shock initiation experiments on 1.60 g/cm3 density (92% TMD) HNS IV have been reported by Schwarz, Bowden et al., Dudley et al., Goveas et al., Greenaway et al., and others. This flyer threshold velocity for detonation/failure data plus measured unreacted HNS Hugoniot data and detonation cylinder test product expansion data were used as the experimental basis for the development of an Ignition and Growth reactive flow model for the shock initiation of HNS IV. The resulting Ignition and Growth HNS IV model parameters yielded good overall agreement with all of this experimental data. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.: Explosive, HNS IV, shock to detonation transition, Ignition and Growth: 82.33.Vx, 82.40.Fp.

  9. Computational model to evaluate port wine stain depth profiling using pulsed photothermal radiometry.

    PubMed

    Choi, Bernard; Majaron, Boris; Nelson, J Stuart

    2004-01-01

    We report on development of an optical-thermal model to evaluate the use of pulsed photothermal radiometry (PPTR) for depth profiling of port wine stain (PWS) skin. In the model, digitized histology sections of a PWS biopsy were used as the input skin geometry. Laser induced temperature profiles were reconstructed from simulated PPTR signals by applying an iterative, non-negatively constrained conjugate gradient algorithm. Accuracy of the following PWS skin characteristics extracted from the reconstructed profiles was determined: (1) average epidermal thickness (z(epi)), (2) maximum epidermal temperature rise (DeltaT(epi,max)), (3) depth of PWS upper boundary (z(PWS)), and (4) depth of maximum PWS temperature rise (z(PWS,max)). Comparison of the actual and reconstructed profiles from PPTR data revealed a good match for all four PWS skin characteristics. Results of this study indicate that PPTR is a viable approach for depth profiling of PWS skin. PMID:15065895

  10. Model of defect reactions and the influence of clustering in pulse-neutron-irradiated Si

    SciTech Connect

    Myers, S. M.; Cooper, P. J.; Wampler, W. R.

    2008-08-15

    Transient reactions among irradiation defects, dopants, impurities, and carriers in pulse-neutron-irradiated Si were modeled taking into account the clustering of the primal defects in recoil cascades. Continuum equations describing the diffusion, field drift, and reactions of relevant species were numerically solved for a submicrometer spherical volume, within which the starting radial distributions of defects could be varied in accord with the degree of clustering. The radial profiles corresponding to neutron irradiation were chosen through pair-correlation-function analysis of vacancy and interstitial distributions obtained from the binary-collision code MARLOWE, using a spectrum of primary recoil energies computed for a fast-burst fission reactor. Model predictions of transient behavior were compared with a variety of experimental results from irradiated bulk Si, solar cells, and bipolar-junction transistors. The influence of defect clustering during neutron bombardment was further distinguished through contrast with electron irradiation, where the primal point defects are more uniformly dispersed.

  11. Modeling and calibration of pulse-modulation based ToF imaging systems

    NASA Astrophysics Data System (ADS)

    Süss, Andreas; Varga, Gabor; Marx, Michael; Fürst, Peter; Gläsener, Stefan; Tiedke, Wolfram; Jung, Melanie; Spickermann, Andreas; Hosticka, Bedrich J.

    2016-03-01

    Conversely to the continuous wave indirect time-of-flight (CW-iToF) imaging scheme, pulsed modulation ToF (PM-iToF) imaging is a promising depth measurement technique for operation at high ambient illumination. It is known that non-linearity and finite charge-transfer speed impact trueness and precision of ToF systems.1-3 As pulses are no Eigenfunctions to the shutter system, this issue is especially pronounced in pulsed modulation.2, 3 Despite these effects, it is possible to find analytical expressions founded on physical observations that map scenery parameters such as depth information, reflectance and ambient light level to sensor output.3, 4 In the application, the inverse of this map has to be evaluated. In PM-iToF, an inverse function cannot be yielded in a direct manner, as models proposed in the literature were transcendental.3, 4 For a limited range an approximating linearization can be performed to yield depth information.5 To extend the usable range, recently, an alternative approach that indirectly approximates the inverse function was presented.6 This method was founded on 1D doping concentration profiles, which, however, are typically not made available to end users. Also, limitations of the 1D approximation as well as stability are yet to be explored. This work presents a calibration methodology that copes with detector insufficiencies such as finite charge transfer speed. Contrarily to the state of the art, no prior knowledge on details of the underlying devices is required. The work covers measurement setup, a benchmark of various calibration schemes and deals with issues such as overfitting or defect pixels.

  12. Numerical studies on the effects of hot end temperature on a single-stage multi-bypass type pulse tube cryocooler

    NASA Astrophysics Data System (ADS)

    Liu, S. X.; Chen, L. B.; Zhou, Y.; Wang, J. J.

    2015-12-01

    The performance of pulse tube cryocooler is affected by the temperature of hot end, which is mainly influenced by the temperature of environment. Effects on a single-stage multibypass type pulse tube cryocooler are investigated by means of numerical simulation. For different opening of multi-bypass orifices, the refrigeration performances are studied when hot end temperature changed in a certain range, and some numerical results are provided and analysed. Together with the temperature at cold head and multi-bypass position, the mass flow rate through the multi-bypass orifice is affected significantly by the temperature of hot end, and the optimum opening of multi-bypass orifice decreases with hot end temperature increasing from 240 K to 320 K. Therefore, to select an optimal opening of bypass orifice according to the temperature of operating environment is necessary.

  13. Maximum two-phase flow rates of subcooled nitrogen through a sharp-edged orifice

    NASA Technical Reports Server (NTRS)

    Simoneau, R. J.

    1975-01-01

    An experiment was conducted and data are presented in which subcooled liquid nitrogen was discharged through a sharp-edged orifice at flow rates near the maximum. The data covered a range of inlet stagnation pressure from slightly above saturation to twice the thermodynamic critical pressure. The data were taken along five separate inlet stagnation isotherms ranging from 0.75 to 1.035 times the thermodynamic critical temperature. The results indicate that: (1) subcooled liquids do not choke or approach maximum flow in an asymptotic manner even though the back pressure is well below saturation; (2) orifice flow coefficients are not constant as is frequently assumed. A metastable jet appears to exist which breaks down if the difference between back pressure and saturation pressure is large enough.

  14. Optical measurements of gas bubbles in oil behind a cavitating micro-orifice flow

    NASA Astrophysics Data System (ADS)

    Iben, Uwe; Wolf, Fabian; Freudigmann, Hans-Arndt; Fröhlich, Jochen; Heller, Winfried

    2015-06-01

    In hydraulic systems, it is common for air release to occur behind valves or throttles in the form of bubbles. These air bubbles can affect the behavior and the performance of these systems to a substantial extent. In the paper, gas release in a liquid flow behind an orifice is analyzed by optical methods for various operation points. The bubbles are observed with a digital camera, and a detection algorithm based on the Hough transformation is used to determine their number and size. The appearance of gas bubbles is very sensitive to the inlet and outlet pressure of the orifice. Gas bubbles are only observed if choking cavitation occurs. An empirical relationship between an adjusted cavitation number and the appearance of gas release is presented. It is assumed that the observed bubbles contain mostly air. With the applied pressure differences, up to 30 % of the dissolved air was degassed in the form of bubbles.

  15. Acoustic gradient-index lens using orifice-type metamaterial unit cells

    NASA Astrophysics Data System (ADS)

    Park, Choon Mahn; Kim, Cho Hee; Park, Hee Tack; Lee, Sang Hun

    2016-03-01

    A gradient-index (GRIN) lens made of acoustic metamaterial is described that is assembled of unit cells with specific orifice characteristics. The GRIN distribution of the lens is established using different hole sizes for the unit cells. The intensity of the sound waves is demonstrated through simulations and confirmed by an experiment in a frequency band that satisfies the homogeneous medium constraints for the metamaterial. Experimental results from the focusing of sound waves of various frequencies agreed well with the expected values from the GRIN lens equation. This face-centered-orifice-cubic unit cell, which is nearly non-dispersive but asymmetric, appears to be a useful acoustic metamaterial for various acoustic devices operating with broadband frequencies.

  16. Natural orifice translumenal endoscopic radical prostatectomy (NOTES RP): the evolution of the technique.

    PubMed

    Humphreys, Mitchell R; Castle, Erik P; Andrews, Paul E

    2012-04-01

    Minimally invasive surgery is advancing to new frontiers that attempt to limit patient morbidities while providing excellent surgical outcomes. At the forefront of these efforts is natural orifice surgery, where surgical incisions can theoretically be eliminated. The purpose of this report is to describe the evolution of the clinical development of the natural orifice translumenal endoscopic radical prostatectomy (NOTES RP). It details the early experimental cadaver and animal work and the many challenges encountered to bring this procedure to clinical fruition. While the procedure remains in its infancy the clinical application to human patients shows its potential merit to positively impact the surgical control of prostate cancer. Early clinical experience does not allow the ability to draw definitive conclusions about the procedure at this time but the potential benefits for a new minimally invasive inexpensive treatment for prostate cancer patients is promising. PMID:22495282

  17. Maximum two-phase flow rates of subcooled nitrogen through a sharp-edged orifice

    NASA Technical Reports Server (NTRS)

    Simoneau, R. J.

    1975-01-01

    Data are presented of an experiment in which subcooled liquid nitrogen was discharged through a sharp-edged orifice at flow rates near the maximum. The data covered a range of inlet stagnation pressures from slightly above saturation to twice the thermodynamic critical pressure. The data were taken along five separate inlet stagnation isotherms ranging from 0.75 to 1.035 times the thermodynamic critical temperature. The results indicate that subcooled liquids do not choke or approach maximum flow in an asymptotic manner even though the back pressure is well below saturation; and orifice flow coefficients are not constant as is frequently assumed. A metastable jet appears to exist which breaks down if the difference between back pressure and saturation pressure is large enough.

  18. Development and performance analysis of a standard orifice flow calibration system

    SciTech Connect

    Akram, H. M.; Maqsood, M.; Rashid, H.

    2009-07-15

    An orifice flow system has been developed indigenously which is a primary standard for the calibration of high vacuum gauges in the range of 10{sup -3}-10{sup -6} mbar. It consists of a constant-volume flow meter, designed to generate a known flow rate of a particular gas to the vacuum chamber. This chamber is partitioned into two parts by a plate with an orifice of calculable conductance. The pressures, generated by this standard system, are compared with those of secondary standard, namely, spinning rotor gauge. Different uncertainties and correction factors are calculated. The maximum percentage deviation is from 1.16% to 0.97%. The combined uncertainties over the entire calibration range of the standard system are in the range of 4.0x10{sup -6} mbar.

  19. A model for the secondary scintillation pulse shape from a gas proportional scintillation counter

    NASA Astrophysics Data System (ADS)

    Kazkaz, K.; Joshi, T. H.

    2016-03-01

    Proportional scintillation counters (PSCs), both single- and dual-phase, can measure the scintillation (S1) and ionization (S2) channels from particle interactions within the detector volume. The signal obtained from these detectors depends first on the physics of the medium (the initial scintillation and ionization), and second how the physics of the detector manipulates the resulting photons and liberated electrons. In this paper we develop a model of the detector physics that incorporates event topology, detector geometry, electric field configuration, purity, optical properties of components, and wavelength shifters. We present an analytic form of the model, which allows for general study of detector design and operation, and a Monte Carlo model which enables a more detailed exploration of S2 events. This model may be used to study systematic effects in current detectors such as energy and position reconstruction, pulse shape discrimination, event topology, dead time calculations, purity, and electric field uniformity. We present a comparison of this model with experimental data collected with an argon gas proportional scintillation counter (GPSC), operated at 20 C and 1 bar, and irradiated with an internal, collimated 55Fe source. Additionally we discuss how the model may be incorporated in Monte Carlo simulations of both GPSCs and dual-phase detectors, increasing the reliability of the simulation results and allowing for tests of the experimental data analysis algorithms.

  20. Pulsed high-intensity focused ultrasound therapy enhances targeted delivery of cetuximab to colon cancer xenograft model in mice.

    PubMed

    Park, Min Jung; Kim, Young-Sun; Yang, Jehoon; Sun, Woo Chul; Park, Hajan; Chae, Sun Young; Namgung, Mi-Sun; Choi, Kyu-Sil

    2013-02-01

    Our aim was to evaluate whether pulsed high-intensity focused ultrasound (HIFU) therapy enhances the effect of an epidermal growth factor receptor-targeted chemotherapeutic drug, cetuximab, in treating human colon cancer xenografts in a mouse model. Balb/c nude mice with subcutaneous xenografts of HT-29 cells were randomly categorized into control (n = 9), pulsed HIFU alone (n = 10), cetuximab monotherapy (n = 8) or combined pulsed HIFU and cetuximab therapy (n = 9) group. Cetuximab, pulsed HIFU therapy, or both were administered three times per week starting from day 8 after tumor cell injection. Based on tumor growth curves up to 34 days, the combination therapy group showed more suppressed tumor growth than all other groups (p < 0.05). The final relative tumor volumes were 5.4 ± 2.1, 5.2 ± 1.3, 4.8 ± 1.8, and 3.1 ± 0.9 for control, pulsed HIFU alone, cetuximab monotherapy, and combination therapy groups, respectively. In conclusion, pulsed HIFU therapy appears to enhance the anti-tumor effect of epidermal growth factor receptor-targeted cetuximab on human colon cancer xenograft models in mice. PMID:23219035

  1. Using Gaussian mixture models to detect and classify dolphin whistles and pulses.

    PubMed

    Peso Parada, Pablo; Cardenal-López, Antonio

    2014-06-01

    In recent years, a number of automatic detection systems for free-ranging cetaceans have been proposed that aim to detect not just surfaced, but also submerged, individuals. These systems are typically based on pattern-recognition techniques applied to underwater acoustic recordings. Using a Gaussian mixture model, a classification system was developed that detects sounds in recordings and classifies them as one of four types: background noise, whistles, pulses, and combined whistles and pulses. The classifier was tested using a database of underwater recordings made off the Spanish coast during 2011. Using cepstral-coefficient-based parameterization, a sound detection rate of 87.5% was achieved for a 23.6% classification error rate. To improve these results, two parameters computed using the multiple signal classification algorithm and an unpredictability measure were included in the classifier. These parameters, which helped to classify the segments containing whistles, increased the detection rate to 90.3% and reduced the classification error rate to 18.1%. Finally, the potential of the multiple signal classification algorithm and unpredictability measure for estimating whistle contours and classifying cetacean species was also explored, with promising results. PMID:24907800

  2. Producing ion waves from acoustic pressure waves in pulsed ICP: Modeling vs. Experiments

    NASA Astrophysics Data System (ADS)

    Despiau-Pujo, Emilie; Cunge, Gilles; Darnon, Maxime; Sadeghi, Nader; Braithwaite, Nicholas

    2015-09-01

    Neutral depletion is an important phenomenon in CW high-density plasmas, mostly caused by gas heating - with a small contribution due to electron pressure Pe - under typical material processing conditions. In pulsed ICP, neutral depletion plays an important role on radical transport in the afterglow. At the beginning of the afterglow, Pe drops rapidly (10 μs) by electron cooling and the gas cools down as well. It generates a neutral pressure gradient between the plasma bulk and the reactor walls, which in turn forces the cold surrounding gas to move rapidly towards the center, thus launching an acoustic wave in the reactor. Fast gas displacement is evidenced by measuring Al atoms drift velocity in the early afterglow of a Cl2/Ar discharge by time-resolved LIF, the acoustic wave in the chamber being observed by mass spectrometry. 2D fluid simulations of Cl2 pulsed ICP predict similar results. These phenomena are further studied during both the plasma ignition and afterglow using modeling and experiments. Strong oscillations are observed both on the Cl2 neutral densities and on the ion flux. As neutrals are pushed towards (or outwards) the chamber walls by the pressure gradient, ions are also pushed in that direction through collisions, as well captured by our ion flux probe.

  3. Solving the quasi-static field model of the pulse-line accelerator; relationship to a circuit model

    SciTech Connect

    Friedman, A

    2006-02-01

    The Pulse-Line Ion Accelerator (PLIA) is a promising approach to high-gradient acceleration of an ion beam at high line charge density [1, 2, 3, 4, 5, 6]. A recent note by R. J. Briggs [7] suggests that a ''sheath helix'' model of such a system can be solved numerically in the quasi-static limit. Such a model captures the correct macroscopic behavior from ''first principles'' without the need to time-advance the full Maxwell equations on a grid. This note describes numerical methods that may be used to effect such a solution, and their connection to the circuit model that was described in an earlier note by the author [8]. Fine detail of the fields in the vicinity of the helix wires is not obtained by this approach, but for purposes of beam dynamics simulation such detail is not generally needed.

  4. Atomistic-continuum modeling of short laser pulse melting of Si targets

    NASA Astrophysics Data System (ADS)

    Lipp, V. P.; Rethfeld, B.; Garcia, M. E.; Ivanov, D. S.

    2014-12-01

    We present an atomistic-continuum model to simulate ultrashort-pulse laser melting processes in semiconductor solids on the example of silicon. The kinetics of transient nonequilibrium phase transition mechanisms is addressed with a molecular dynamics method at atomic level, whereas the laser light absorption, strong generated electron-phonon nonequilibrium, fast diffusion of and heat conduction due to photoexcited free carriers are accounted for in the continuum. We give a detailed description of the model, which is then applied to study the mechanism of short laser pulse melting of freestanding Si films. The effect of laser-induced pressure and temperature of the lattice on the melting kinetics is investigated. Two competing melting mechanisms, heterogeneous and homogeneous, were identified. Apart from the classical heterogeneous melting mechanism, the nucleation of the liquid phase homogeneously inside the material significantly contributes to the melting process. The simulations showed, that due to the open diamond structure of the crystal, the laser-generated internal compressive stresses reduce the crystal stability against the homogeneous melting. Consequently, the latter can take a massive character within several picoseconds upon the laser heating. Due to the negative volume of melting of modeled Si material, -7.5%, the material contracts upon the phase transition, relaxes the compressive stresses, and the subsequent melting proceeds heterogeneously until the excess of thermal energy is consumed. The threshold fluence value, at which homogeneous nucleation of liquid starts contributing to the classical heterogeneous propagation of the solid-liquid interface, is found from the series of simulations at different laser input fluences. For the example of Si, the laser melting kinetics of semiconductors was found to be noticeably different from that of metals with a fcc crystal structure.

  5. Mathematical modeling of selective photothermolysis to aid the treatment of vascular malformations and hemangioma with pulsed dye laser.

    PubMed

    Shafirstein, Gal; Buckmiller, Lisa M; Waner, Milton; Bäumler, Wolfgang

    2007-06-01

    Pulsed dye lasers (PDL) are the standard of care in the treatment of cutaneous vascular disorders such as the port-wine strains or hemangiomas of infancy. Nonetheless, there is still uncertainty regarding the specific laser parameters that are likely to yield optimal clinical outcomes. Using mathematical modeling, we explain and associate clinical outcomes with laser wavelength, radiant exposure, and pulse time and shape. The model's prediction that a continuous PDL pulse of 0.45 ms with a radiant exposure of 6 J/cm(2) is equivalent to delivering a 1.5-ms pulse consisting of three pulses with a radiant exposure of 12 J/cm(2) is in agreement with clinical studies. The model also suggests that for vascular malformations involving vessel diameters in the range of 150-500 microm, one should use a PDL at a wavelength of 595 nm with a radiant exposure of at least 12 J/cm(2) and pulse time of 1.5 ms, delivered in three pulses. Whereas it is calculated that malformations with vessels smaller than 50 microm will not respond to PDL in any clinical setting, an excellent response to PDL treatment at either a 585- or 595-nm wavelength can be expected for malformations with vessel diameters of 50-150 microm. Epidermal cooling is highly recommended for all settings to minimize pain and the risk of side effects. Finally, the model is used to generate a reference table that suggests specific PDL parameters for the treatment of various malformations and hemangiomas. The table cannot replace a clinician's experience with respect to which and how parameters should be changed, but provides a defined window of parameters that should be tried to improve clinical response. PMID:17268765

  6. Recognition of root canal orifices at a distance - a preliminary study of teledentistry.

    PubMed

    Brüllmann, Dan; Schmidtmann, Irene; Warzecha, Katharina; d'Hoedt, Bernd

    2011-01-01

    The remote recognition of root canal orifices was tested on 50 images of endodontically accessed teeth acquired with an intra-oral camera. The images were stored on a laptop computer and were presented to 20 observers who marked the visible canal orifices using software which stored the canal locations in standard files. The marked positions were verified on histological slices. In 87% of the cases, the canal locations were marked correctly. Inter-observer reliability depended on the location of the reviewed root canal (kappa = 0.44-0.77). The detection rate was related to the professional experience of the observers. The maximum proportion of accurate detections was found for the observers with more than 10 years of professional experience. The minimum proportion of accurate detections, 79%, was by the observer with one year of experience. The results of the study suggest that remote recognition of root canals by experienced dentists can help younger colleagues in the detection of root canal orifices. PMID:21339303

  7. Coronal microleakage of three different dental biomaterials as intra-orifice barrier during nonvital bleaching

    PubMed Central

    Zarenejad, Nafiseh; Asgary, Saeed; Ramazani, Nahid; Haghshenas, Mohammad Reza; Rafiei, Alireza; Ramazani, Mohsen

    2015-01-01

    Background: This study was designed to assess the microleakage of glass-ionomer (GI), mineral trioxide aggregate (MTA), and calcium-enriched mixture (CEM) cement as coronal orifice barrier during walking bleaching. Materials and Methods: In this experimental study, endodontic treatment was done for 70 extracted human incisors without canal calcification, caries, restoration, resorption, or cracks. The teeth were then divided into three experimental using “Simple randomization allocation” (n = 20) and two control groups (n = 5). The three cements were applied as 3-mm intra-orifice barrier in test groups, and bleaching process was then conducted using a mixture of sodium perborate powder and distilled water, for 9 days. For leakage evaluation, bovine serum albumin marker was traced in a dual-chamber technique with Bradford indicator. The Kruskal-Wallis and Mann-Whitney tests were used for statistical analysis. Results: The mean ± standard deviation leakage of samples from negative control, positive control, GI, MTA, and CEM cement groups were 0.0, 8.9 ± 0.03, 0.47 ± 0.02, 0.48 ± 0.02, and 0.49 ± 0.02 mg/mL, respectively. Statistical analysis showed no significant difference between three experimental groups (P > 0.05). Conclusion: It is concluded that GI, MTA, and CEM cements are considered as suitable intra-orifice barrier to provide coronal seal during walking bleaching. PMID:26759596

  8. Pneumatic hammer in aerostatic thrust bearings with single orifice compensation

    NASA Astrophysics Data System (ADS)

    Kong, Zhongke; Tao, Jizhong

    2013-01-01

    In dealing with the phenomenon of the pneumatic hammer in aerostatic thrust bearings, the vibrant model of the one-single freedom system has been established to study the pneumatic hammer from the point of sympathetic vibration. It is found that the bearings show a tendency to result in the pneumatic hammer with the increase of air supply pressure, and the occurrence probability of the pneumatic hammer will be reduced when the gas film thickness is maintained within a certain range. Meanwhile, the existence of the pneumatic hammer, which is caused by sympathetic vibration, is experimentally verified, and it is found that gas bearings undergo certain disturbance, which causes the system to produce micro breadth vibration. Accordingly, the micro breadth vibration causes the gas film and thrust face to form flow/structure coupled to excite the pneumatic hammer. Therefore, it provides another path to study the pneumatic hammer and is of academic value.

  9. Investigation into pulse laser heating of nanoscale Au film using dual-phase-lag model.

    PubMed

    Ho, Ching-Yen; Tsai, Yu-Hsiang; Chen, Bor-Chyuan

    2013-10-01

    In this study the thermal field is presented for pulse laser processing of nanoscale Au films. Fourier law is inadequate for describing the heat conduction in nanoscale process due to the boundary scattering and the finite relaxation time of heat carriers. In the regime where the particle description of electrons and phonons is valid, the Boltzmann equation is the most accurate option to model heat transfer in such problems. However, solving the Boltzmann equation is generally difficult due to involving three spatial, three momentums and one time. Dual-phase-lag (DPL) model is averaged over the momentum space and thus involves only spatial coordinates plus time, as in the Fourier equation. Therefore this paper utilizes the dual-phase-lag (DPL) model with scattering boundary condition to study the temperature field for laser processing of nanometer-sized thin films instead of Boltzmann equation. The results obtained from the dual-phase-lag heat conduction model, hyperbolic and parabolic heat conduction equations were compared with the available experimental data to validate the compatibility of the thermal models for analyzing the heat transfer in nanoscale thin film irradiated by laser. The temperature history at different locations of the thin film and the effects of boundary phonon scattering on the normalized temperature were also discussed. PMID:24245230

  10. Modelling inactivation of Listeria monocytogenes by pulsed electric fields in media of different pH.

    PubMed

    Gómez, N; García, D; Alvarez, I; Condón, S; Raso, J

    2005-08-25

    A study of the effect of square-wave pulsed electric fields (PEF) on the inactivation of Listeria monocytogenes in McIlvaine buffer of different pH (3.5-7.0) was conducted. L. monocytoges was more PEF sensitive at higher electric field strengths (E) and in media of low pH. A treatment at 28 kV/cm for 400 mus that inactivated 1.5, 2.3 and 3.0 Log10 cycles at pH 7.0, 6.5 and 5.0 respectively destroyed almost 6.0 Log10 cycles at pH 3.5. The general shape of survival curves of L. monocytogenes PEF treated at different pH was convex/concave upwards. A mathematical model based on the Weibull distribution accurately described these survival curves. At each pH, the shape parameter (n value) did not depend on E. The relationship between n value of the Weibull model and the pH of the treatment medium was described by the Gompertz equation. A multiple linear regression model using three predictor variables (E, E2, pH2) related the Log10 of the scale paramenter (b value) of the Weibull model with E and pH of the treatment medium. A tertiary model developed using McIlvaine buffer as treatment medium predicted satisfactorily the inactivation of L. monocytogenes in apple juice. PMID:16083822

  11. Diagnostic accuracy of a mathematical model to predict apnea–hypopnea index using nighttime pulse oximetry

    NASA Astrophysics Data System (ADS)

    Ebben, Matthew R.; Krieger, Ana C.

    2016-03-01

    The intent of this study is to develop a predictive model to convert an oxygen desaturation index (ODI) to an apnea-hypopnea index (AHI). This model will then be compared to actual AHI to determine its precision. One thousand four hundred and sixty-seven subjects given polysomnograms with concurrent pulse oximetry between April 14, 2010, and February 7, 2012, were divided into model development (n=733) and verification groups (n=734) in order to develop a predictive model of AHI using ODI. Quadratic regression was used for model development. The coefficient of determination (r2) between the actual AHI and the predicted AHI (PredAHI) was 0.80 (r=0.90), which was significant at a p<0.001. The areas under the receiver operating characteristic curve ranged from 0.96 for AHI thresholds of ≥10 and ≥15/h to 0.97 for thresholds of ≥5 and ≥30/h. The algorithm described in this paper provides a convenient and accurate way to convert ODI to a predicted AHI. This tool makes it easier for clinicians to understand oximetry data in the context of traditional measures of sleep apnea.

  12. A kinetic model for estimating net photosynthetic rates of cos lettuce leaves under pulsed light.

    PubMed

    Jishi, Tomohiro; Matsuda, Ryo; Fujiwara, Kazuhiro

    2015-04-01

    Time-averaged net photosynthetic rate (P n) under pulsed light (PL) is known to be affected by the PL frequency and duty ratio, even though the time-averaged photosynthetic photon flux density (PPFD) is unchanged. This phenomenon can be explained by considering that photosynthetic intermediates (PIs) are pooled during light periods and then consumed by partial photosynthetic reactions during dark periods. In this study, we developed a kinetic model to estimate P n of cos lettuce (Lactuca sativa L. var. longifolia) leaves under PL based on the dynamics of the amount of pooled PIs. The model inputs are average PPFD, duty ratio, and frequency; the output is P n. The rates of both PI accumulation and consumption at a given moment are assumed to be dependent on the amount of pooled PIs at that point. Required model parameters and three explanatory variables (average PPFD, frequency, and duty ratio) were determined for the simulation using P n values under PL based on several combinations of the three variables. The model simulation for various PL levels with a wide range of time-averaged PPFDs, frequencies, and duty ratios further demonstrated that P n under PL with high frequencies and duty ratios was comparable to, but did not exceed, P n under continuous light, and also showed that P n under PL decreased as either frequency or duty ratio was decreased. The developed model can be used to estimate P n under various light environments where PPFD changes cyclically. PMID:25736464

  13. Freshwater pulse experiments in a coupled climate model with bistable AMOC: testing the theory

    NASA Astrophysics Data System (ADS)

    Graham, T.; Jackson, L.; Menary, M.; Palmer, M.

    2012-04-01

    A collapse of the Atlantic meridional overturning circulation (AMOC) could have severe consequences for the climate of Northern Europe and may impact the climate of the whole planet (e.g. Vellinga and Wood, 2002). Several paleoclimate studies have suggested that such events have occurred in the past and may have been responsible for large shifts in Earth's climate. Although such events have been simulated in simple box models and models of intermediate complexity most GCMs have been unable to produce these events. Several recent papers (e.g. Rammstorf, 1999; Pardaens et al., 2003; Drijfhout et al., 2010, Hawkins et al., 2011) have suggested that the direction of freshwater transport by the AMOC at the southern boundary of the Atlantic Ocean (Fov) may be crucial to the stability of the AMOC. Observational estimates suggest that the AMOC exports freshwater from the Atlantic Ocean (Fov < 0) whereas in almost all models without flux adjustments the AMOC imports freshwater (Fov > 0). The latest UK Met Office Hadley Centre climate model (HadGEM3) has a negative Fov as a result of reduced upper ocean salinity biases in the South Atlantic. This suggests that the AMOC may be less stable than in previous models. We will present the first results from a series of freshwater pulse experiments where freshwater is rapidly added to the North Atlantic Ocean to see whether the AMOC will collapse, and furthermore whether it will recover to its initial state.

  14. Simple Two-Dimensional Corrections for One-Dimensional Pulse Tube Models

    NASA Technical Reports Server (NTRS)

    Lee, J. M.; Kittel, P.; Timmerhaus, K. D.; Radebaugh, R.

    2004-01-01

    One-dimensional oscillating flow models are very useful for designing pulse tubes. They are simple to use, not computationally intensive, and the physical relationship between temperature, pressure and mass flow are easy to understand when used in conjunction with phasor diagrams. They do not possess, however, the ability to directly calculate thermal and momentum diffusion in the direction transverse to the oscillating flow. To account for transverse effects, lumped parameter corrections, which are obtained though experiment, must be used. Or two-dimensional solutions of the differential fluid equations must be obtained. A linear two-dimensional solution to the fluid equations has been obtained. The solution provides lumped parameter corrections for one-dimensional models. The model accounts for heat transfer and shear flow between the gas and the tube. The complex Nusselt number and complex shear wall are useful in describing these corrections, with phase relations and amplitudes scaled with the Prandtl and Valensi numbers. The calculated ratio, a, between a two-dimensional solution of the oscillating temperature and velocity and a one-dimensional solution for the same shows a scales linearly with Va for Va less than 30. In this region alpha less than 0.5, that is, the enthalpy flow calculated with a two-dimensional model is 50% of a calculation using a one-dimensional model. For Va greater than 250, alpha = 0.8, showing that diffusion is still important even when it is confined to a thing layer near the tube wall.

  15. Model experiment of cosmic ray acceleration due to an incoherent wakefield induced by an intense laser pulse

    SciTech Connect

    Kuramitsu, Y.; Sakawa, Y.; Takeda, K.; Tampo, M.; Takabe, H.; Nakanii, N.; Kondo, K.; Tsuji, K.; Kimura, K.; Fukumochi, S.; Kashihara, M.; Tanimoto, T.; Nakamura, H.; Ishikura, T.; Kodama, R.; Mima, K.; Tanaka, K. A.; Mori, Y.; Miura, E.; Kitagawa, Y.

    2011-01-15

    The first report on a model experiment of cosmic ray acceleration by using intense laser pulses is presented. Large amplitude light waves are considered to be excited in the upstream regions of relativistic astrophysical shocks and the wakefield acceleration of cosmic rays can take place. By substituting an intense laser pulse for the large amplitude light waves, such shock environments were modeled in a laboratory plasma. A plasma tube, which is created by imploding a hollow polystyrene cylinder, was irradiated by an intense laser pulse. Nonthermal electrons were generated by the wakefield acceleration and the energy distribution functions of the electrons have a power-law component with an index of {approx}2. The maximum attainable energy of the electrons in the experiment is discussed by a simple analytic model. In the incoherent wakefield the maximum energy can be much larger than one in the coherent field due to the momentum space diffusion or the energy diffusion of electrons.

  16. Kinetic Monte Carlo simulations of travelling pulses and spiral waves in the lattice Lotka-Volterra model

    NASA Astrophysics Data System (ADS)

    Makeev, Alexei G.; Kurkina, Elena S.; Kevrekidis, Ioannis G.

    2012-06-01

    Kinetic Monte Carlo simulations are used to study the stochastic two-species Lotka-Volterra model on a square lattice. For certain values of the model parameters, the system constitutes an excitable medium: travelling pulses and rotating spiral waves can be excited. Stable solitary pulses travel with constant (modulo stochastic fluctuations) shape and speed along a periodic lattice. The spiral waves observed persist sometimes for hundreds of rotations, but they are ultimately unstable and break-up (because of fluctuations and interactions between neighboring fronts) giving rise to complex dynamic behavior in which numerous small spiral waves rotate and interact with each other. It is interesting that travelling pulses and spiral waves can be exhibited by the model even for completely immobile species, due to the non-local reaction kinetics.

  17. A multiscale, hierarchical model of pulse dynamics in arid-land ecosystems

    USGS Publications Warehouse

    Collins, Scott L.; Belnap, Jayne; Grimm, N. B.; Rudgers, J. A.; Dahm, Clifford N.; D'Odorico, P.; Litvak, M.; Natvig, D. O.; Peters, Douglas C.; Pockman, W. T.; Sinsabaugh, R. L.; Wolf, B. O.

    2014-01-01

    Ecological processes in arid lands are often described by the pulse-reserve paradigm, in which rain events drive biological activity until moisture is depleted, leaving a reserve. This paradigm is frequently applied to processes stimulated by one or a few precipitation events within a growing season. Here we expand the original framework in time and space and include other pulses that interact with rainfall. This new hierarchical pulse-dynamics framework integrates space and time through pulse-driven exchanges, interactions, transitions, and transfers that occur across individual to multiple pulses extending from micro to watershed scales. Climate change will likely alter the size, frequency, and intensity of precipitation pulses in the future, and arid-land ecosystems are known to be highly sensitive to climate variability. Thus, a more comprehensive understanding of arid-land pulse dynamics is needed to determine how these ecosystems will respond to, and be shaped by, increased climate variability.

  18. Laser shock peening and warm laser shock peening: process modeling and pulse shape influence

    NASA Astrophysics Data System (ADS)

    Fortunato, Alessandro; Orazi, Leonardo; Cuccolini, Gabriele; Ascari, Alessandro

    2013-02-01

    Laser shock peening is a well-known technology able to enhance the fatigue life of mechanical components by means of the introduction of residual stresses on their surface. These stresses are induced by means of the recoil pressure caused by the abrupt expansion, in a confining medium, of a laser-vaporized coating layer. If high power densities are used the recoil pressure can be high enough to induce compressive residual stresses on the target surface and to modify its mechanical properties. These mechanical properties can be predicted if the recoil pressure of the ablating layer is determined. In this paper the influence of the laser pulse shape on the recoil pressure is determined by means of a proper modeling of the whole process and the difference between cold" and warm" laser shock peening is pointed out.

  19. Modeling studies of a turbulent pulsed jet flame using LES/PDF

    NASA Astrophysics Data System (ADS)

    Zhang, Pei; Wang, Haifeng

    2015-11-01

    The combustion field in a pulsed turbulent piloted jet flame is studied using an advanced large eddy simulation (LES) / probability density function (PDF) method. Measurement data with a joint OH-PLIF/OH* chemiluminescence/LDV system are available including the temporal series of the axial velocity and planar OH images. A time-dependent inflow condition is specified based on the measurement data. A direct comparison of the mean and rms velocities from the calculations and from the measurement shows a satisfactory prediction of the flow fields by using the employed modeling methods. The predicted OH mass fractions are compared qualitatively with the measured OH images at selected temporal and spatial locations. The comparison shows a good agreement. Conditional quantities and flame index are extracted from the simulations to examine the bimodal and multi-regime combustion dynamics in the flame. This paper is based upon work supported by the National Science Foundation under Grant No. CBET-1336075.

  20. Relativistic laser piston model: Ponderomotive ion acceleration in dense plasmas using ultraintense laser pulses

    NASA Astrophysics Data System (ADS)

    Schlegel, T.; Naumova, N.; Tikhonchuk, V. T.; Labaune, C.; Sokolov, I. V.; Mourou, G.

    2009-08-01

    Laser ponderomotive force at superhigh intensities provides an efficient ion acceleration in bulk dense targets and evacuates a channel enabling further laser beam propagation. The developed quasistationary model of a laser piston—a double layer structure supported by the radiation pressure—predicts the general parameters of the acceleration process in homogeneous and inhomogeneous overdense plasmas. Particle-in-cell simulations confirm the estimated characteristics in a wide range of laser intensities and ion densities and show advantages of circularly polarized laser pulses. Two nonstationary effects are identified in the simulations. First, oscillations of the piston velocity and of the thickness of the ion charge separation layer broaden the energy spectrum of accelerated ions. Second, the electrons accelerated toward the incoming laser wave emit strong high-frequency radiation, enabling a cooling effect, which helps to sustain high charge neutrality in the piston and to maintain an efficient ion acceleration.

  1. Dimensionless heat transfer model to compress and analyze pulsed thermography data for NDT of materials

    NASA Astrophysics Data System (ADS)

    Ramirez-Granados, Juan C.; Paez, G.; Strojnik, M.

    2008-03-01

    We develop a dimensionless heat transfer model to analyze pulsed thermography data for non-destructive testing (NDT) of materials. Simulated thermographic sequences are used in order to evaluate the performance of the inspection technique. Also, we inspect organic and inorganic samples, including a layered plate and two dental pieces, in search of internal defects and structural inhomogeneities. We detect cavities and the inner structure of the samples by means of reconstructed thermograms and a modified version of the differential absolute contrast (DAC). Moreover, we develop an effective data compression method that reduces a thermographic video with m frames of p × q pixels to two matrices of p × q elements. In this data reconstruction process, precision and compression ratio are independent parameters. Finally, we find that partial translucency of dental enamel, in infrared, permits imaging of the internal structure of a tooth. This inspection technique does not require a priori knowledge about a reference defect-free area.

  2. Enthalpy modulation of a laminar pulsed nitrogen arc jet: time-resolved diagnostics and model

    NASA Astrophysics Data System (ADS)

    Rat, V.; Krowka, J.; Coudert, J. F.

    2015-08-01

    In most studies, plasma spraying of liquid feedstock for ceramic coating elaboration requires limiting the arc motion to obtain stable plasma and to favour homogeneous treatment of nanomaterials. In this chapter, an alternative approach is proposed and consists of using a pulsed arc jet modulating the specific enthalpy in time. The momentum and heat transfers can be controlled provided a synchronous injection of materials is associated with it. The rotational temperatures of the nitrogen arc jet are measured by means of time-resolved optical emission spectroscopy synchronized with the arc voltage. The enthalpy modulation ratio (hmax/hmin) is shown to be close to 2.68. A simplified model of the dynamics of heat transfers is used to interpret diagnostics and highlights a time delay between arc voltage and enthalpy at the nozzle exit due to the characteristic time of heat transfers and residence time of plasma.

  3. Ablation model for semiconductors and dielectrics under ultrafast laser pulses for solar cells micromachining

    NASA Astrophysics Data System (ADS)

    Gurizzan, Alberto; Villoresi, Paolo

    2015-01-01

    Ultrafast laser pulses provide a new tool for material processing. The ultrafast regime leads to nonlinear absorption and nonthermal interaction with the target yielding significant advantages in solar cells micromachining over traditional mechanical or Q-switched laser processes: high process speed, high energetic efficiency, reduced heat affected zone (HAZ), high quality and precision of the realized structures. Therefore, a description of the dominant physical processes underlying the ultrafast laser-matter interaction is needed to develop a simplified model able to provide an explanation of the different aspect of the process. This paper provides an overview of the fundamental equations governing the laser-material interaction process in a typical dielectric-semiconductor structure and discusses the solution on a 3D axisymmetric domain obtained with a finite element method (FEM) software applied to the problem of selective dielectric delamination in PV solar cells.

  4. Fluid modeling of a high-voltage nanosecond pulsed xenon microdischarge

    NASA Astrophysics Data System (ADS)

    Levko, Dmitry; Raja, Laxminarayan L.

    2016-07-01

    A computational modeling study of high-voltage nanosecond pulsed microdischarge in xenon gas at 10 atm is presented. The discharge is observed to develop as two streamers originating from the cathode and the anode, and propagating toward each other until they merge to form a single continuous discharge channel. The peak plasma density obtained in the simulations is ˜1024 m-3, i.e., the ionization degree of plasma does not exceed 1%. The influence of the initial gas pre-ionization is established. It is seen that an increase in the seeded plasma density results in an increase in the streamer propagation velocity and an increase in the plasma density obtained after the merging of two streamers.

  5. Electrical characterization and modeling of pulse-based forming techniques in RRAM arrays

    NASA Astrophysics Data System (ADS)

    Grossi, Alessandro; Zambelli, Cristian; Olivo, Piero; Miranda, Enrique; Stikanov, Valeriy; Walczyk, Christian; Wenger, Christian

    2016-01-01

    The forming process, which corresponds to the activation of the switching filament in Resistive Random Access Memory (RRAM) arrays, has a strong impact on the cells' performances. In this paper we characterize and compare different pulse forming techniques in terms of forming time, yield and cell-to-cell variability on 4 kbits RRAM arrays. Moreover, post-forming modeling during Reset operation of correctly working and over formed cells has been performed. An incremental form and verify technique, based on a sequence of trapezoidal waveforms with increasing voltages followed by a verify operation that terminates when the expected switching behavior has been achieved, showed the best results. This procedure narrows the post-forming current distribution whereas reducing the Reset switching voltage and the operative current. These advantages materialize in a better control of the cell-to-cell variability and in an overall time and energy saving at the system level.

  6. Reduced rank models for travel time estimation of low order mode pulses.

    PubMed

    Chandrayadula, Tarun K; Wage, Kathleen E; Worcester, Peter F; Dzieciuch, Matthew A; Mercer, James A; Andrew, Rex K; Howe, Bruce M

    2013-10-01

    Mode travel time estimation in the presence of internal waves (IWs) is a challenging problem. IWs perturb the sound speed, which results in travel time wander and mode scattering. A standard approach to travel time estimation is to pulse compress the broadband signal, pick the peak of the compressed time series, and average the peak time over multiple receptions to reduce variance. The peak-picking approach implicitly assumes there is a single strong arrival and does not perform well when there are multiple arrivals due to scattering. This article presents a statistical model for the scattered mode arrivals and uses the model to design improved travel time estimators. The model is based on an Empirical Orthogonal Function (EOF) analysis of the mode time series. Range-dependent simulations and data from the Long-range Ocean Acoustic Propagation Experiment (LOAPEX) indicate that the modes are represented by a small number of EOFs. The reduced-rank EOF model is used to construct a travel time estimator based on the Matched Subspace Detector (MSD). Analysis of simulation and experimental data show that the MSDs are more robust to IW scattering than peak picking. The simulation analysis also highlights how IWs affect the mode excitation by the source. PMID:24116527

  7. Analysis of pulsed eddy current data using regression models for steam generator tube support structure inspection

    NASA Astrophysics Data System (ADS)

    Buck, J. A.; Underhill, P. R.; Morelli, J.; Krause, T. W.

    2016-02-01

    Nuclear steam generators (SGs) are a critical component for ensuring safe and efficient operation of a reactor. Life management strategies are implemented in which SG tubes are regularly inspected by conventional eddy current testing (ECT) and ultrasonic testing (UT) technologies to size flaws, and safe operating life of SGs is predicted based on growth models. ECT, the more commonly used technique, due to the rapidity with which full SG tube wall inspection can be performed, is challenged when inspecting ferromagnetic support structure materials in the presence of magnetite sludge and multiple overlapping degradation modes. In this work, an emerging inspection method, pulsed eddy current (PEC), is being investigated to address some of these particular inspection conditions. Time-domain signals were collected by an 8 coil array PEC probe in which ferromagnetic drilled support hole diameter, depth of rectangular tube frets and 2D tube off-centering were varied. Data sets were analyzed with a modified principal components analysis (MPCA) to extract dominant signal features. Multiple linear regression models were applied to MPCA scores to size hole diameter as well as size rectangular outer diameter tube frets. Models were improved through exploratory factor analysis, which was applied to MPCA scores to refine selection for regression models inputs by removing nonessential information.

  8. Bidirectional transport and pulsing states in a multi-lane ASEP model

    NASA Astrophysics Data System (ADS)

    Lin, Congping; Steinberg, Gero; Ashwin, Peter

    2011-09-01

    In this paper, we introduce an ASEP-like transport model for bidirectional motion of particles on a multi-lane lattice. The model is motivated by in vivo experiments on organelle motility along a microtubule (MT), consisting of thirteen protofilaments, where particles are propelled by molecular motors (dynein and kinesin). In the model, organelles (particles) can switch directions of motion due to 'tug-of-war' events between counteracting motors. Collisions of particles on the same lane can be cleared by switching to adjacent protofilaments (lane changes). We analyse transport properties of the model with no-flux boundary conditions at one end of a MT ('plus end' or tip). We show that the ability to make lane changes can affect the transport efficiency and the particle-direction change rate obtained from experiments is close to optimal for achieving efficient motor and organelle transport in a living cell. In particular, we find a nonlinear scaling of the mean tip size (the number of particles accumulated at the tip) with injection rate and an associated phase transition leading to pulsing states characterized by periodic filling and emptying of the system.

  9. Mixing of Multiple Jets With a Confined Subsonic Crossflow. Part 2; Opposed Rows of Orifices in Rectangular Ducts

    NASA Technical Reports Server (NTRS)

    Holdeman, James D.; Liscinsky, David S.; Bain, Daniel B.

    1997-01-01

    This paper summarizes experimental and computational results on the mixing of opposed rows of jets with a confined subsonic crossflow in rectangular ducts. The studies from which these results were excerpted investigated flow and geometric variations typical of the complex 3-D flowfield in the combustion chambers in gas turbine engines. The principal observation was that the momentum-flux ratio, J, and the orifice spacing, S/H, were the most significant flow and geometric variables. Jet penetration was critical, and penetration decreased as either momentum-flux ratio or orifice spacing decreased. It also appeared that jet penetration remained similar with variations in orifice size, shape, spacing, and momentum-flux ratio when the orifice spacing was inversely proportional to the square-root of the momentum-flux ratio. It was also seen that planar averages must be considered in context with the distributions. Note also that the mass-flow ratios and the offices investigated were often very large (jet-to-mainstream mass-flow ratio greater than 1 and the ratio of orifices-area-to-mainstream-cross-sectional-area up to 0.5 respectively), and the axial planes of interest were often just downstream of the orifice trailing edge. Three-dimensional flow was a key part of efficient mixing and was observed for all configurations.

  10. A theoretical study of the acoustic impedance of orifices in the presence of a steady grazing flow

    NASA Technical Reports Server (NTRS)

    Rice, E. J.

    1976-01-01

    An analysis of the oscillatory fluid flow in the vicinity of a circular orifice with a steady grazing flow is presented. The study is similar to that of Hersh and Rogers but with the addition of the grazing flow. Starting from the momentum and continuity equations, a considerably simplified system of partial differential equations is developed with the assumption that the flow can be described by an oscillatory motion superimposed upon the known steady flow. The equations are seen to be linear in the region where the grazing flow effects are dominant, and a solution and the resulting orifice impedance are presented for this region. The nonlinearity appears to be unimportant for the usual conditions found in aircraft noise suppressors. Some preliminary conclusions of the study are that orifice resistance is directly proportional to grazing flow velocity (known previously from experimental data) and that the orifice inductive (mass reactance) end correction is not a function of grazing flow. This latter conclusion is contrary to the widely held notion that grazing flow removes the effect of the orifice inductive end correction. This conclusion also implies that the experimentally observed total inductance reduction with grazing flow might be in the flow within the orifice rather than in the end correction.

  11. Size distributions of fly ash using Coulter Multisizer: Use of multiple orifices and fitting to truncated log-normal distributions

    SciTech Connect

    Ghosal, S.; Ebert, J.L.; Self, S.A.

    1991-11-01

    Fly ash particles, which are predominantly spherical and glassy, are produced by melting of the mineral inclusions in the coal during combustion. Particle diameters can range from sub-micrometer (micron or {mu}m) to greater than 100 {mu}m. The size distribution of fly ash is needed to determine its role in the radiation transfer process in pulverized coal combustors. The Coulter Multisizer is an useful instrument for sizing powders with a broad size distribution. A single Multisizer orifice can size particles only within a specific size range limited at the lower end to a few percent of orifice diameter by sensitivity and at the upper end by increasing non-linearity of the signal-volume relation. A scheme for combining data obtained using orifices of different diameters is described. The manufacturers state that the smallest particle which can be sized accurately is nominally 2% of the diameter of the orifice. However, it was found that the data for particles less than 4% of the orifice diameter were not reliable. In order to use the smaller orifices, the larger particles have to be removed from the sample. A wet-sieving apparatus, designed for accurate separation of the particles by size, is described. A log-normal distribution function, truncated outside the measurement limits, fits the size distribution data well. Size parameters for fly ashes of six representative US coals are presented.

  12. Perspective on modeling tailored-pulse loading (TPL) for borehole stimulation

    SciTech Connect

    Swift, R P

    1984-08-01

    Realizing the full potential of gas-bearing deposits, such as the Eastern Devonian gas shales, requires an increased understanding of Tailored-Pulse Loading (TPL) stimulation techniques to initiate and extend multiple fractures. This is demonstrated in discussions of TPL phenomenology and of the limitations of past and current models to fully account for the mutual dependence of the governing processes and constraints. The processes include non-linear material deformation, porous flow, fracture, and fluid flow in fractures; the constraints consist of in-situ stresses, saturation, natural fractures and joints, and the TPL-source characteristics. Comprehensive modeling is one which unifies models governing each process with conditions defining the constraints, and accounts for their interaction in a coupled manner. An approach is proposed to model TPL in a unified manner that is hybrid in nature: it involves the use of state-of-the-art models combining both numerical and analytical solutions; the numerical solutions will be based both on finite-element and finite-difference algorithms. Efforts are defined to focus on the fracture initiation phase in parallel with the fracture extension phase for multiple fracturing. Various micro and macro fracture models with the coupling of porous flow effects will be under consideration for the initiation phase. Analyses of multiple fracture extension phase will include the treatment of fractures as being discrete, the influence of natural discontinuities such as joints and existing fractures, and the viscous behavior of fluid flow within fractures and joints. In addition, the linking of models for the initiation and extension phases within the framework of a single code will be pursued. 97 references, 3 figures.

  13. 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

  14. Pulse!!: a model for research and development of virtual-reality learning in military medical education and training.

    PubMed

    Dunne, James R; McDonald, Claudia L

    2010-07-01

    Pulse!! The Virtual Clinical Learning Lab at Texas A&M University-Corpus Christi, in collaboration with the United States Navy, has developed a model for research and technological development that they believe is an essential element in the future of military and civilian medical education. The Pulse!! project models a strategy for providing cross-disciplinary expertise and resources to educational, governmental, and business entities challenged with meeting looming health care crises. It includes a three-dimensional virtual learning platform that provides unlimited, repeatable, immersive clinical experiences without risk to patients, and is available anywhere there is a computer. Pulse!! utilizes expertise in the fields of medicine, medical education, computer science, software engineering, physics, computer animation, art, and architecture. Lab scientists collaborate with the commercial virtual-reality simulation industry to produce research-based learning platforms based on cutting-edge computer technology. PMID:23634475

  15. Using a hybrid-fluid model to simulate the ion-hose instability in long-pulse electron linacs

    NASA Astrophysics Data System (ADS)

    Carlsten, Bruce E.

    2005-11-01

    A numerical model of the ion-hose instability for long-pulse electron linacs is presented, where the ion motion is represented by fluid parameters. In order to gain extra numerical stability, the fluid behavior of the ions is evolved via particle-in-cell (PIC) techniques. This methodology provides a much faster simulation than a full PIC calculation, allowing for end-to-end simulations of the ion-hose instability in actual linear accelerator configurations. After the description of the simulation model and some simple test cases, the instability is analyzed for a variety of nominal accelerator transport conditions. Simulations of the instability are provided for sections of the DARHT long-pulse accelerator that show different growth regimes of the instability. We find that large-amplitude growth is possible in accelerator and transport regions lacking uniform external focusing, for electron pulse lengths of 2μsec and longer.

  16. Analytic model and frequency characteristics of plasma synthetic jet actuator

    NASA Astrophysics Data System (ADS)

    Zong, Hao-hua; Wu, Yun; Li, Ying-hong; Song, Hui-min; Zhang, Zhi-bo; Jia, Min

    2015-02-01

    This paper reports a novel analytic model of a plasma synthetic jet actuator (PSJA), considering both the heat transfer effect and the inertia of the throat gas. Both the whole cycle characteristics and the repetitive working process of PSJA can be predicted with this model. The frequency characteristics of a PSJA with 87 mm3 volume and different orifice diameters are investigated based on the analytic model combined with experiments. In the repetitive working mode, the actuator works initially in the transitional stage with 20 cycles and then in the dynamic balanced stage. During the transitional stage, major performance parameters of PSJA experience stepped growth, while during the dynamic balanced stage, these parameters are characterized by periodic variation. With a constant discharge energy of 6.9 mJ, there exists a saturated frequency of 4 kHz/6 kHz for an orifice diameter of 1 mm/1.5 mm, at which the time-averaged total pressure of the pulsed jet reaches a maximum. Between 0.5 mm and 1.5 mm, a larger orifice diameter leads to a higher saturated frequency due to the reduced jet duration time. As the actuation frequency increases, both the time-averaged cavity temperature and the peak jet velocity initially increase and then remain almost unchanged at 1600 K and 280 m/s, respectively. Besides, with increasing frequency, the mechanical energy incorporated in single pulsed jet, the expelled mass per pulse, and the time-averaged density in the cavity, decline in a stair stepping way, which is caused by the intermittent decrease of refresh stage duration in one period.

  17. Analytical modeling of transport aircraft crash scenarios to obtain floor pulses

    NASA Technical Reports Server (NTRS)

    Wittlin, G.; Lackey, D.

    1983-01-01

    The KRAS program was used to analyze transport aircraft candidate crash scenarios. Aircraft floor pulses and seat/occupant responses are presented. Results show that: (1) longitudinal only pulses can be represented by equivalent step inputs and/or static requirements; (2) the L1649 crash test floor longitudinal pulse for the aft direction (forward inertia) is less than 9g static or an equivalent 5g pulse; aft inertia accelerations are extremely small ((ch76) 3g) for representative crash scenarios; (3) a viable procedure to relate crash scenario floor pulses to standard laboratory dynamic and static test data using state of the art analysis and test procedures was demonstrated; and (4) floor pulse magnitudes are expected to be lower for wide body aircraft than for smaller narrow body aircraft.

  18. Modeling of cluster organization in metal-doped oxide glasses irradiated by a train of femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Smetanina, Evgeniya; Chimier, Benoit; Petit, Yannick; Varkentina, Nadezda; Fargin, Evelyne; Hirsch, Lionel; Cardinal, Thierry; Canioni, Lionel; Duchateau, Guillaume

    2016-01-01

    The formation of silver cluster structures at submicrometer spatial scales under the irradiation by high-power femtosecond laser pulses with high repetition rate was observed in various glasses containing silver ions. In order to account for the formation of these structures in metal-doped glasses, we present a theoretical model for the organization of noble metallic clusters induced by a train of femtosecond laser pulses. The model includes photoionization and laser heating of the sample, diffusion, kinetic reactions, and dissociation of metallic species. This model was applied to reproduce the formation of cluster structures in silver-doped phosphate glass. The parameters of the silver structures were obtained numerically under various incident pulse intensities and number of pulses. Numerical modeling shows that the involved microscopic physical and chemical processes naturally lead to the emergence of a silver cluster organization, together with charge migration and subsequent trapping giving rise to a strong static electric field buried in the irradiated area as experimentally observed. Based on this modeling, a theoretical basis is provided for the design of new metallic cluster structures with nanoscale size.

  19. Discontinuous nonequilibrium phase transitions in a nonlinearly pulse-coupled excitable lattice model

    NASA Astrophysics Data System (ADS)

    Assis, Vladimir R. V.; Copelli, Mauro

    2009-12-01

    We study a modified version of the stochastic susceptible-infected-refractory-susceptible (SIRS) model by employing a nonlinear (exponential) reinforcement in the contagion rate and no diffusion. We run simulations for complete and random graphs as well as d -dimensional hypercubic lattices (for d=3,2,1 ). For weak nonlinearity, a continuous nonequilibrium phase transition between an absorbing and an active phase is obtained, such as in the usual stochastic SIRS model [Joo and Lebowitz, Phys. Rev. E 70, 036114 (2004)]. However, for strong nonlinearity, the nonequilibrium transition between the two phases can be discontinuous for d≥2 , which is confirmed by well-characterized hysteresis cycles and bistability. Analytical mean-field results correctly predict the overall structure of the phase diagram. Furthermore, contrary to what was observed in a model of phase-coupled stochastic oscillators with a similar nonlinearity in the coupling [Wood , Phys. Rev. Lett. 96, 145701 (2006)], we did not find a transition to a stable (partially) synchronized state in our nonlinearly pulse-coupled excitable elements. For long enough refractory times and high enough nonlinearity, however, the system can exhibit collective excitability and unstable stochastic oscillations.

  20. Real-time robot path planning based on a modified pulse-coupled neural network model.

    PubMed

    Qu, Hong; Yang, Simon X; Willms, Allan R; Yi, Zhang

    2009-11-01

    This paper presents a modified pulse-coupled neural network (MPCNN) model for real-time collision-free path planning of mobile robots in nonstationary environments. The proposed neural network for robots is topologically organized with only local lateral connections among neurons. It works in dynamic environments and requires no prior knowledge of target or barrier movements. The target neuron fires first, and then the firing event spreads out, through the lateral connections among the neurons, like the propagation of a wave. Obstacles have no connections to their neighbors. Each neuron records its parent, that is, the neighbor that caused it to fire. The real-time optimal path is then the sequence of parents from the robot to the target. In a static case where the barriers and targets are stationary, this paper proves that the generated wave in the network spreads outward with travel times proportional to the linking strength among neurons. Thus, the generated path is always the global shortest path from the robot to the target. In addition, each neuron in the proposed model can propagate a firing event to its neighboring neuron without any comparing computations. The proposed model is applied to generate collision-free paths for a mobile robot to solve a maze-type problem, to circumvent concave U-shaped obstacles, and to track a moving target in an environment with varying obstacles. The effectiveness and efficiency of the proposed approach is demonstrated through simulation and comparison studies. PMID:19775961

  1. Optimal pulse penetration in Lorentz-Model dielectrics using the Sommerfeld and Brillouin precursors.

    PubMed

    Oughstun, Kurt Edmund

    2015-10-01

    Under proper initial conditions, the interrelated effects of phase and attenuation dispersion in ultrawideband pulse propagation modify the input pulse into precursor fields. Because of their minimal decay in a given dispersive medium, precursor-type pulses possess optimal penetration into that material at the frequency-chirped Lambert-Beer's law limit, making them ideally suited for remote sensing and medical imaging. PMID:26480173

  2. Energy budget of a propagating pulse in discrete and continuum fault models and its implications on models for scale dependence of strength

    NASA Astrophysics Data System (ADS)

    Heaton, T. H.; Elbanna, A. E.

    2009-12-01

    We study scale dependence of strength in dynamical systems failing at multiple length scales and its physical basis. We show that, for a spring block slider model, the strength defined as the energy per unit slip per unit rupture length decreases as a power law as the rupture length increases with the scaling exponent varying between 0 (the plastic limit) and -0.5 (the brittle limit). We conjecture that the physical basis of this scaling is in the pulse-like nature of the propagating rupture on velocity weakening (VW) interfaces which results in larger events having higher slip rates and lower dynamic friction. As a consequence, large amplitude slip pulses have less frictional work per unit slip (our definition of strength) than do small amplitude slip pulses. Since large amplitude pulses are also associated with long ruptures, the strength decreases with the physical size of the system. We investigate the energy budget in numerical simulations of the highly nonlinear multi-degree-of-freedom slider model. We construct an equation of motion (ODE) that approximately describes the spatial/temporal evolution of a slip pulse as it propagates along the slip surface. In order to extend this approach to an elastic continuum, we need to quantify the intrinsic energy of a slip pulse. We present a rational definition for the pulse energy based on the kinetic energy of the motions in the medium due to the propagating rupture. We study the spatial variation of the kinetic energy density for a slip pulse in a 2D anti-plane fault model and conclude that, for a given slip, the narrower the pulse the larger the kinetic energy associated with it and the smaller the region in which this energy is concentrated in. We also examine the relation between the pulse energy defined this way and the seismic radiated energy and propose an energy balance equation, analogous to the one derived for the spring block model, with the pulse energy as one of its components. Our future plans include

  3. Porcine skin visible lesion thresholds for near-infrared lasers including modeling at two pulse durations and spot sizes

    NASA Astrophysics Data System (ADS)

    Cain, Clarence P.; Polhamus, Garrett D.; Roach, William P.; Stolarski, David J.; Schuster, Kurt J.; Stockton, Kevin; Rockwell, Benjamin A.; Chen, Bo; Welch, Ashley J.

    2006-07-01

    With the advent of such systems as the airborne laser and advanced tactical laser, high-energy lasers that use 1315-nm wavelengths in the near-infrared band will soon present a new laser safety challenge to armed forces and civilian populations. Experiments in nonhuman primates using this wavelength have demonstrated a range of ocular injuries, including corneal, lenticular, and retinal lesions as a function of pulse duration. American National Standards Institute (ANSI) laser safety standards have traditionally been based on experimental data, and there is scant data for this wavelength. We are reporting minimum visible lesion (MVL) threshold measurements using a porcine skin model for two different pulse durations and spot sizes for this wavelength. We also compare our measurements to results from our model based on the heat transfer equation and rate process equation, together with actual temperature measurements on the skin surface using a high-speed infrared camera. Our MVL-ED50 thresholds for long pulses (350 µs) at 24-h postexposure are measured to be 99 and 83 Jcm-2 for spot sizes of 0.7 and 1.3 mm diam, respectively. Q-switched laser pulses of 50 ns have a lower threshold of 11 Jcm-2 for a 5-mm-diam top-hat laser pulse.

  4. Interaction of a turbulent boundary layer with a cavity-backed circular orifice and tonal acoustic excitation

    NASA Astrophysics Data System (ADS)

    Zhang, Qi; Bodony, Daniel

    2013-11-01

    Acoustic liners are effective reducers of jet exhaust and core noise and work by converting acoustic-bound energy into non-radiating, vorticity-bound energy through scattering, viscous, and non-linear processes. Modern liners are designed using highly-calibrated semi-empirical models that will not be effective for expected parameter spaces on future aircraft. The primary model limitation occurs when a turbulent boundary layer (TBL) grazes the liner; there are no physics-based methods for predicting the sound-liner interaction. We thus utilize direct numerical simulations to study the interaction of a Mach 0.5 zero pressure gradient TBL with a cavity-backed circular orifice under acoustic excitation. Acoustic field frequencies span the energy-containing range within the TBL and amplitudes range from 6 to 40 dB above the turbulent fluctuations. Impedance predictions are in agreement with NASA Langley-measured data and the simulation databases are analyzed in detail. A physics-based reduced-order model is proposed that connects the turbulence-vorticity-acoustic interaction and its accuracy and limitations are discussed. This work is funded by Aeroacoustics Research Consortium.

  5. Modeling and Numerical Simulation of Microwave Pulse Propagation in Air Breakdown Environment

    NASA Technical Reports Server (NTRS)

    Kuo, S. P.; Kim, J.

    1991-01-01

    Numerical simulation is used to investigate the extent of the electron density at a distant altitude location which can be generated by a high-power ground-transmitted microwave pulse. This is done by varying the power, width, shape, and carrier frequency of the pulse. The results show that once the breakdown threshold field is exceeded in the region below the desired altitude location, electron density starts to build up in that region through cascading breakdown. The generated plasma attenuates the pulse energy (tail erosion) and thus deteriorates the energy transmission to the destined altitude. The electron density saturates at a level limited by the pulse width and the tail erosion process. As the pulse continues to travel upward, though the breakdown threshold field of the background air decreases, the pulse energy (width) is reduced more severely by the tail erosion process. Thus, the electron density grows more quickly at the higher altitude, but saturates at a lower level. Consequently, the maximum electron density produced by a single pulse at 50 km altitude, for instance, is limited to a value below 10(exp 6) cm(exp -3). Three different approaches are examined to determine if the ionization at the destined location can be improved: a repetitive pulse approach, a focused pulse approach, and two intersecting beams. Only the intersecting beam approach is found to be practical for generating the desired density level.

  6. The impact of thermally pulsing asymptotic giant branch stars on hierarchical galaxy formation models

    NASA Astrophysics Data System (ADS)

    Tonini, Chiara; Maraston, Claudia; Devriendt, Julien; Thomas, Daniel; Silk, Joseph

    2009-06-01

    The spectro-photometric properties of galaxies in galaxy formation models are obtained by combining the predicted history of star formation and mass accretion with the physics of stellar evolution through stellar population models. In the recent literature, significant differences have emerged regarding the implementation of the thermally pulsing asymptotic giant branch phase of stellar evolution. The emission in the TP-AGB phase dominates the bolometric and near-IR spectrum of intermediate-age (~1Gyr) stellar populations, hence it is crucial for the correct modelling of the galaxy luminosities and colours. In this paper, for the first time, we incorporate a full prescription of the TP-AGB phase in a semi-analytic model of galaxy formation. We find that the inclusion of the TP-AGB in the model spectra dramatically alters the predicted colour-magnitude relation and its evolution with redshift. When the TP-AGB phase is active, the rest-frame V - K galaxy colours are redder by almost 2 mag in the redshift range z ~ 2-3 and by 1 mag at z ~ 1. Very red colours are produced in disc galaxies, so that the V - K colour distributions of disc and spheroids are virtually undistinguishable at low redshifts. We also find that the galaxy K-band emission is more than 1 mag higher in the range z ~ 1-3. This may alleviate the difficulties met by the hierarchical clustering scenario in predicting the red galaxy population at high redshifts. The comparison between simulations and observations has to be revisited in the light of our results.

  7.  Note: High temperature pulsed solenoid valve

    NASA Astrophysics Data System (ADS)

    Shen, Wei; Sulkes, Mark

    2010-01-01

    We have developed a high temperature pulsed solenoid valve with reliable long term operation to at least 400 °C. As in earlier published designs, a needle extension sealing a heated orifice is lifted via solenoid actuation; the solenoid is thermally isolated from the heated orifice region. In this new implementation, superior sealing and reliability were attained by choosing a solenoid that produces considerably larger lifting forces on the magnetically actuated plunger. It is this property that facilitates easily attainable sealing and reliability, albeit with some tradeoff in attainable gas pulse durations. The cost of the solenoid valve employed is quite low and the necessary machining quite simple. Our ultimate level of sealing was attained by making a simple modification to the polished seal at the needle tip. The same sealing tip modification could easily be applied to one of the earlier high T valve designs, which could improve the attainability and tightness of sealing for these implementations.

  8. A note on traveling fronts and pulses in a firing rate model of a neuronal network

    NASA Astrophysics Data System (ADS)

    Enculescu, M.

    2004-09-01

    We study the activity of a one-dimensional synaptically coupled neural network by means of a firing rate model developed by Coombes et al. [Physica D 178 (2003)]. Their approach incorporates the biologically motivated finite conduction velocity of action potentials into a neural field equation of Wilson and Cowan type [Kybernetik 13 (1973)]. The resulting integro-differential equation with a space depending delay term under the convolution may exhibit a variety of traveling and stationary patterns. In this paper we construct traveling wave solutions for the case of a firing rate given by the Heaviside step function, exponential synaptic kernel, and exponential synaptic footprint. In contrast to Coombes et al., where the model equation is first reduced to an equivalent system of partial differential equations, we make the traveling pattern ansatz into the initial integro-differential equation. We analyse two types of traveling patterns: fronts and pulses, for which we derive shape and speed. We further determine necessary conditions for the linear stability of the traveling waves.

  9. Highlighting the DNA damage response with ultrashort laser pulses in the near infrared and kinetic modeling

    PubMed Central

    Ferrando-May, Elisa; Tomas, Martin; Blumhardt, Philipp; Stöckl, Martin; Fuchs, Matthias; Leitenstorfer, Alfred

    2013-01-01

    Our understanding of the mechanisms governing the response to DNA damage in higher eucaryotes crucially depends on our ability to dissect the temporal and spatial organization of the cellular machinery responsible for maintaining genomic integrity. To achieve this goal, we need experimental tools to inflict DNA lesions with high spatial precision at pre-defined locations, and to visualize the ensuing reactions with adequate temporal resolution. Near-infrared femtosecond laser pulses focused through high-aperture objective lenses of advanced scanning microscopes offer the advantage of inducing DNA damage in a 3D-confined volume of subnuclear dimensions. This high spatial resolution results from the highly non-linear nature of the excitation process. Here we review recent progress based on the increasing availability of widely tunable and user-friendly technology of ultrafast lasers in the near infrared. We present a critical evaluation of this approach for DNA microdamage as compared to the currently prevalent use of UV or VIS laser irradiation, the latter in combination with photosensitizers. Current and future applications in the field of DNA repair and DNA-damage dependent chromatin dynamics are outlined. Finally, we discuss the requirement for proper simulation and quantitative modeling. We focus in particular on approaches to measure the effect of DNA damage on the mobility of nuclear proteins and consider the pros and cons of frequently used analysis models for FRAP and photoactivation and their applicability to non-linear photoperturbation experiments. PMID:23882280

  10. Dynamic complexities in a pest control model with birth pulse and harvesting

    NASA Astrophysics Data System (ADS)

    Goel, A.; Gakkhar, S.

    2016-04-01

    In this paper, an impulsive model is discussed for an integrated pest management approach comprising of chemical and mechanical controls. The pesticides and harvesting are used to control the stage-structured pest population. The mature pest give birth to immature pest in pulses at regular intervals. The pest is controlled by spraying chemical pesticides affecting immature as well as mature pest. The harvesting of both immature and mature pest further reduce the pest population. The discrete dynamical system obtained from stroboscopic map is analyzed. The threshold conditions for stability of pest-free state as well as non-trivial period-1 solution is obtained. The effect of pesticide spray timing and harvesting on immature as well as mature pest are shown. Finally, by numerical simulation with MATLAB, the dynamical behaviors of the model is found to be complex. Above the threshold level there is a characteristic sequence of bifurcations leading to chaotic dynamics. Route to chaos is found to be period-doubling. Period halving bifurcations are also observed.

  11. Modeling the influence of anode cathode spacing in a pulsed discharge nozzle

    NASA Astrophysics Data System (ADS)

    Broks, B. H. P.; Brok, W. J. M.; Remy, J.; van der Mullen, J. J. A. M.; Benidar, A.; Biennier, L.; Salama, F.

    2005-11-01

    The pulsed discharge nozzle (PDN) is a spectrochemical source that is designed to produce and cool molecular ions in an astrophysically relevant environment in the laboratory with limited fragmentation. In order to gain a better understanding of the PDN and to optimize the yield of molecular ions and radicals in the PDN source, a parameter study of the influence of the interelectrode distance on the plasma properties is carried out by means of a discharge model, providing a qualitative as well as a quantitative picture of the plasma. We model the electron density and energy, as well as the argon ion and metastable atom number density for various interelectrode distances. The results reveal that increasing the interelectrode distance does not significantly influence the plasma at the cathode and at the anode. However, a positive column forms between the electrodes, which increases in length as the interelectrode distance increases. This is an additional evidence that the PDN is a glow discharge. This positive column does not contribute significantly to the formation of metastable argon atoms. Because metastable argon is thought to be the primary agent in the formation of molecular ions through Penning ionization of the neutral molecular precursor there is no benefit to be expected from an increase of the interelectrode distance. In fact, electron impact dissociation of the molecules in the column might even make the source less efficient for longer column lengths. The simulations presented here provide physical insight into the characteristics of interstellar species analogs in laboratory experiments.

  12. Mathematical model of strip specimens for application of pulse-heating technique

    NASA Astrophysics Data System (ADS)

    Xiao, Peng; Wang, Qingwei; Dai, Jingmin

    2008-10-01

    The dynamic measurement of selected thermophysical properties of electrically conducting solids in the temperature range of 1100 K to the melting point was conducted using strip specimens, for simultaneous measurement of the normal spectral emissivity by using integrating sphere reflectometry. The method is based on rapid resistive self-heating of the specimen from room temperature to any desired high temperature in less than several seconds by the passage of an electical current pulse through it to measure the pertinent quantities, as current, voltage, and randiance temperature, with sub-millisecond resolution. The estimation of heat capacity and hemispherical total emissivity is based on various computational methods derived by assuming that the temperature was uniform in the central part of the specimen. The validity of this approach was verified when specimens with large cross sections and when the temperature on the specimen surface was measured. A numerical model was established with the temperature variations across the specimen was taken into consideration. The mathematical model established can be used in the simulation experiments to access the magnitude of specific phenomena due to the temperature gradient inside the specimen, in relation to the specimen geometry and to the specific thermophysical properties of different materials.

  13. Modeling double pulsing of ion beams for HEDP target heating experiments

    NASA Astrophysics Data System (ADS)

    Veitzer, Seth; Barnard, John; Stoltz, Peter; Henestroza, Enrique

    2008-04-01

    Recent research on direct drive targets using heavy ion beams suggests optimal coupling will occur when the energy of the ions increases over the course of the pulse. In order to experimentally explore issues involving the interaction of the beam with the outflowing blowoff from the target, double pulse experiments have been proposed whereby a first pulse heats a planar target producing an outflow of material, and a second pulse (˜10 ns later) of higher ion energy (and hence larger projected range) interacts with this outflow before reaching and further heating the target. We report here results for simulations of double pulsing experiments using HYDRA for beam and target parameters relevant to the proposed Neutralized Drift Compression Experiment (NDCX) II at LBNL.

  14. On the Resolution Limit of Femtosecond Stimulated Raman Spectroscopy: Modelling Fifth-Order Signals with Overlapping Pulses.

    PubMed

    Fumero, Giuseppe; Batignani, Giovanni; Dorfman, Konstantin E; Mukamel, Shaul; Scopigno, Tullio

    2015-11-16

    Femtosecond stimulated Raman scattering (FSRS) spectroscopy is a powerful pump-probe technique that can track electronic and vibrational dynamics with high spectral and temporal resolution. The investigation of extremely short-lived species, however, implies deciphering complex signals and is ultimately hampered by unwanted nonlinear effects once the time resolution limit is approached and the pulses overlap temporally. Using the loop diagrams formalism we calculate the fifth-order response of a model system and address the limiting case where the relevant dynamics timescale is comparable to the pump-pulse duration and, consequently, the pump and the probe overlap temporally. We find that in this regime, additional diagrams that do not contribute for temporally well separated pulses need to be taken into account, giving rise to new time-dependent features, even in the absence of photoinduced dynamics and for negative delays. PMID:26387662

  15. Role of energy input model on the remediation of the p-Nitrophenol contaminated over-wet soil by pulsed corona discharge plasma

    NASA Astrophysics Data System (ADS)

    Wang, C. H.; Zhang, X.; Wang, T. C.; Lu, N.; Li, J.; Wu, Y.

    2013-03-01

    Low-temperature plasma has exhibited high efficiency for fast remediation of organic-polluted soil with water content (less than 20%). In the present study, the feasibility of remediation of p-Nitrophenol (PNP) contaminated over-wet soil (water content of 100%) was studied using pulsed corona discharge plasma, which was generated in a needle-plate discharge reactor. Effect of energy input model, including pulse voltage and pulse frequency on PNP degradation, was studied. Experimental results showed that about 86.3% of PNP could be smoothly removed after 60 min discharge treatment. PNP degradation efficiency increased with an increase in pulse voltage or pulse frequency, due to the enhancement of energy input. Existence of water contributed to H2O2 generation and the amount of exhausted H2O2 increased with pulse voltage. This study is expected to provide an alternative method for remediation of contaminated soil containing much water by pulsed discharge plasma without drying pretreatment.

  16. Experiments on flow through one to four inlets of the orifice and Borda type

    NASA Technical Reports Server (NTRS)

    Hendricks, R. C.; Stetz, T. T.

    1981-01-01

    Choked flow rate and pressure profile data were taken on sequential axially aligned inlets of the orifice and Borda type. The configuration consisted of from two to four inlets spaced at two nominal separation distances of 0.7 and 30 diameters. At the nominal 30 diameter spacing, the reduced flow rate follows a simple empirical relation based on the reduced flow rate for a single inlet. At the nominal 0.7 diameter spacing, fluid jetting was prevalent at low temperatures and flow rates were the same as for a single inlet.

  17. Active control of crossflow-induced transition by means of in-line pneumatic actuator orifices

    NASA Astrophysics Data System (ADS)

    Lohse, J.; Barth, H. P.; Nitsche, W.

    2016-08-01

    The possibility of a pneumatic actuator system for controlling the crossflow vortex-induced laminar breakdown is investigated by means of hot-wire measurements. Steady blowing or suction through a spanwise row of periodically arranged orifices initiates a system of longitudinal vortices which reduces the amplitude of the most amplified stationary crossflow vortices. Thus, the onset of high-frequency secondary instability and the following laminar-turbulent transition was shifted farther downstream. All experiments were conducted at the redesigned DLR swept flat plate experiment in the open test section of the 1 m wind tunnel at the DLR in Göttingen.

  18. Performance of a High-Speed Compression-Ignition Engine Using Multiple Orifice Fuel Injection Nozzles

    NASA Technical Reports Server (NTRS)

    Spanogle, J A; Foster, H H

    1930-01-01

    This report presents test results obtained at the Langley Memorial Aeronautical Laboratory of the National Advisory Committee for Aeronautics during an investigation to determine the relative performance of a single-cylinder, high-speed, compression-ignition engine when using fuel injection valve nozzles with different numbers, sizes, and directions of round orifices. A spring-loaded, automatic injection valve was used, centrally located at the top of a vertical disk-type combustion chamber formed between horizontally opposed inlet and exhaust valves of a 5 inch by 7 inch engine.

  19. Model of propagation of acoustic pulses caused by underground nuclear explosion and theirs influence on the ionosphere

    NASA Astrophysics Data System (ADS)

    Krasnov, V.; Drobzheva, Y.

    2003-04-01

    To describe the propagation of an acoustic pulse through the inhomogeneity atmosphere we developed new equation and correspondent computer simulation code. The equation takes into account nonlinear effects, inhomogeneities of the atmosphere, absorption, expansion of a wave acoustic front, etc. The model includes subroutine of vertical movement of earth surface during an underground nuclear explosion (we use an empirical model), subroutine of acoustic pulse generation by a spall zone, subroutine of propagation of acoustic pulse up to the ionospheric height, subroutine of acoustic wave influence on the ionospheric plasma, subroutine of ionospheric perturbation influence on Doppler frequency of a radio wave. All calculations take into account geomagnetic field and neutral wind. The data measurement of acoustic pulses at heights of the ionosphere with helping Doppler radio sounding were used to test the model. We used data of Doppler shift records which were obtained during 9 underground nuclear explosion for 16 traces of radio sounding of the ionoshphere. Coefficients correlation between calculated and experimental forms is 0.7-0.94.

  20. Lumped-element model of a tapered transmission line for impedance matching in a pulsed power system

    NASA Astrophysics Data System (ADS)

    Lee, Kun-A.; Ko, Kwang-Cheol

    2016-07-01

    In a pulsed power system, impedance matching is one of the significant factors for increasing the efficiency of the system. One of the most general methods for impedance matching is to use a tapered transmission line. Because the characteristics of a tapered transmission line are changed continuously according to its position, modeling the tapered transmission line by using lumped elements is difficult. In this study, we investigated a tapered transmission line to match the impedance of power supply to that of a load by using lumped elements especially in a pulsed power system. In modeling the tapered transmission line, we used the concept of a transmission, and we introduced an efficient modeling method. We propose a simulation model based on the investigation results. The results of the study will be useful for research on tapered transmission lines.

  1. A hybrid model for simulation of secondary electron emission in plasma immersion ion implantation under different pulse rise time

    SciTech Connect

    Navab Safa, N. Ghomi, H.

    2015-02-15

    A hybrid fluid Particle in Cell–Monte Carlo Collision (PiC–MCC) model is presented to study the effect of secondary electron emission on the plasma immersion ion implantation process under different pulse rise time. The model describes the temporal evolution of various parameters of plasma such as ion density, ion velocity, secondary electron density, and secondary electron current for different rise times. A 3D–3 V PiC–MCC model is developed to simulate the secondary electrons which are emitted from the sample surface while the plasma ions and electrons are treated using a 1D fluid model. The simulation results indicate that the secondary electron density and secondary electron current increase as the rise time decreases. The main differences between the results for different rise times are found during the initial phase of the pulse. The results are explained through studying the fundamental parameters of plasma.

  2. Numerical Model of Channel and Aquatic Habitat Response to Sediment Pulses in Mountain Rivers of Central Idaho

    NASA Astrophysics Data System (ADS)

    Lewicki, M.; Buffington, J. M.; Thurow, R. F.; Isaak, D. J.

    2006-12-01

    Mountain rivers in central Idaho receive pulsed sediment inputs from a variety of mass wasting processes (side-slope landslides, rockfalls, and tributary debris flows). Tributary debris flows and hyperconcentrated flows are particularly common due to winter "rain-on-snow" events and summer thunderstorms, the effects of which are amplified by frequent wildfire and resultant changes in vegetation, soil characteristics, and basin hydrology. Tributary confluences in the study area are commonly characterized by debris fans built by these repeated sediment pulses, providing long-term controls on channel slope, hydraulics and sediment transport capacity in the mainstem channel network. These long-term impacts are magnified during debris-flow events, which deliver additional sediment and wood debris to the fan and may block the mainstem river. These changes in physical conditions also influence local and downstream habitat for aquatic species, and can impact local human infrastructure (roads, bridges). Here, we conduct numerical simulations using a modified version of Cui's [2005] network routing model to examine bedload transport and debris-fan evolution in medium- sized watersheds (65-570 km2) of south-central Idaho. We test and calibrate the model using data from a series of postfire debris-flow events that occurred from 2003-4. We investigate model sensitivity to different controlling factors (location of the pulse within the stream network, volume of the pulse, and size distribution of the input material). We predict that on decadal time scales, sediment pulses cause a local coarsening of the channel bed in the vicinity of the sediment input, and a wave of downstream fining over several kilometers of the river (as long as the pulse material is not coarser than the stream bed itself). The grain-size distribution of the pulse influences its rate of erosion, the rate and magnitude of downstream fining, and the time required for system recovery. The effects of textural

  3. Passive-Damping of the Axial Run-Out for High Speed Rotating Flexible Optical Disk Using the Idea of Damping Orifice

    NASA Astrophysics Data System (ADS)

    Gad, Abdelrasoul M. M.; Rhim, Yoon Chul

    2010-08-01

    In the present work, the idea of damping orifice is applied so as to reduce the axial run-out of a high speed rotating flexible optical disk. A track or more of rectangular-edge orifices is inscribed in a rigid flat stabilizer near the outer region of the disk that exhibits large vibration amplitudes. The effects of the orifice geometry, number of orifices per track, and the number of tracks are investigated experimentally. The results from this study show that the introduced new design of the stabilizer can reduce the axial run-out of the disk at 10,000 rpm to within 10 µm over its entire span using two tracks of damping orifices near the disk rim. The study proved that the introduced orifices in the flat stabilizer effectively enhance the damping capability of the air-film to dissipate the vibration energy of the rotating disk.

  4. Climate-Based Models for Pulsed Resources Improve Predictability of Consumer Population Dynamics: Outbreaks of House Mice in Forest Ecosystems

    PubMed Central

    Holland, E. Penelope; James, Alex; Ruscoe, Wendy A.; Pech, Roger P.; Byrom, Andrea E.

    2015-01-01

    Accurate predictions of the timing and magnitude of consumer responses to episodic seeding events (masts) are important for understanding ecosystem dynamics and for managing outbreaks of invasive species generated by masts. While models relating consumer populations to resource fluctuations have been developed successfully for a range of natural and modified ecosystems, a critical gap that needs addressing is better prediction of resource pulses. A recent model used change in summer temperature from one year to the next (ΔT) for predicting masts for forest and grassland plants in New Zealand. We extend this climate-based method in the framework of a model for consumer–resource dynamics to predict invasive house mouse (Mus musculus) outbreaks in forest ecosystems. Compared with previous mast models based on absolute temperature, the ΔT method for predicting masts resulted in an improved model for mouse population dynamics. There was also a threshold effect of ΔT on the likelihood of an outbreak occurring. The improved climate-based method for predicting resource pulses and consumer responses provides a straightforward rule of thumb for determining, with one year’s advance warning, whether management intervention might be required in invaded ecosystems. The approach could be applied to consumer–resource systems worldwide where climatic variables are used to model the size and duration of resource pulses, and may have particular relevance for ecosystems where global change scenarios predict increased variability in climatic events. PMID:25785866

  5. Climate-based models for pulsed resources improve predictability of consumer population dynamics: outbreaks of house mice in forest ecosystems.

    PubMed

    Holland, E Penelope; James, Alex; Ruscoe, Wendy A; Pech, Roger P; Byrom, Andrea E

    2015-01-01

    Accurate predictions of the timing and magnitude of consumer responses to episodic seeding events (masts) are important for understanding ecosystem dynamics and for managing outbreaks of invasive species generated by masts. While models relating consumer populations to resource fluctuations have been developed successfully for a range of natural and modified ecosystems, a critical gap that needs addressing is better prediction of resource pulses. A recent model used change in summer temperature from one year to the next (ΔT) for predicting masts for forest and grassland plants in New Zealand. We extend this climate-based method in the framework of a model for consumer-resource dynamics to predict invasive house mouse (Mus musculus) outbreaks in forest ecosystems. Compared with previous mast models based on absolute temperature, the ΔT method for predicting masts resulted in an improved model for mouse population dynamics. There was also a threshold effect of ΔT on the likelihood of an outbreak occurring. The improved climate-based method for predicting resource pulses and consumer responses provides a straightforward rule of thumb for determining, with one year's advance warning, whether management intervention might be required in invaded ecosystems. The approach could be applied to consumer-resource systems worldwide where climatic variables are used to model the size and duration of resource pulses, and may have particular relevance for ecosystems where global change scenarios predict increased variability in climatic events. PMID:25785866

  6. Investigation on Effects of Die Orifice Layout on Three-Hole Porthole Extrusion of Aluminum Alloy 6063 Tubes

    NASA Astrophysics Data System (ADS)

    Zhang, Cunsheng; Zhao, Guoqun; Chen, Hao; Guan, Yanjin; Cai, Haijin; Gao, Baojie

    2013-05-01

    Currently, with the increasing demand of high production output, much attention is paid to the research and development of multi-hole extrusion die. However, owing to the complexity of multi-hole porthole extrusion technology, it has not been applied widely in practice for the production of aluminum profiles, especially for porthole die with an odd number of die orifices. The purpose of this study is to design a three-hole porthole die for producing an aluminum tube and to optimize the location of die orifices based on computer-aided design and engineering. First, three-hole extrusion dies for different locations of die orifices are designed. Then, extrusion processes with different multi-hole porthole dies are simulated by means of HyperXtrude. Through numerical simulation, metal flow, temperature distribution, welding pressure, extrusion load, and die stress, etc. could be obtained, and the effects of the location of die orifices on extrusion process are investigated. With the increasing distance between die orifice and extrusion center (described as eccentricity ratio), metal flow becomes nonhomogeneous, and twisting or bending deformation of profile occurs, but the welding pressure rises, which improves the welding quality of profiles. However, the required extrusion force, billet and die temperature, die displacement, and stress induce no significant changes. In comparison with the extrusion force during single-hole porthole extrusion, there is 18.5% decrease of extrusion force during three-hole porthole extrusion. Finally, design rules for this kind of multi-hole extrusion dies are summarized.

  7. Short Shock Pulse Duration Experiments Plus Ignition and Growth Modeling on Composition B

    NASA Astrophysics Data System (ADS)

    May, Chadd; Tarver, Craig

    2013-06-01

    Short pulse duration shock initiation experiments were performed on 1.71 g/cm3 Composition B using electrically driven kapton flyer plates. Critical impact velocities for initiation at several flyer plate thicknesses and diameters were determined. For 2 mm diameter flyers, the critical velocities for shock initiation ranged from 4.06 to 4.72 km/s for flyer thicknesses ranging from 127 to 50.8 microns. Since the failure diameter of Composition B is approximately 4 mm, the kapton flyers imparted sufficient energy to overcome the effects of both rear and size rarefaction wave energy loses and cause detonation. The Ignition and Growth reactive flow model parameters for Composition B were modified to include unreacted Hugoniot, detonation reaction zone, and overdriven detonation experimental data and then applied to the kapton flyer data with good results. This work was performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.: Explosive, Composition B, shock to detonation transition, Ignition and Growth: 82.33.Vx, 82.40.Fp.

  8. A 1D pulse wave propagation model of the hemodynamics of calf muscle pump function.

    PubMed

    Keijsers, J M T; Leguy, C A D; Huberts, W; Narracott, A J; Rittweger, J; van de Vosse, F N

    2015-07-01

    The calf muscle pump is a mechanism which increases venous return and thereby compensates for the fluid shift towards the lower body during standing. During a muscle contraction, the embedded deep veins collapse and venous return increases. In the subsequent relaxation phase, muscle perfusion increases due to increased perfusion pressure, as the proximal venous valves temporarily reduce the distal venous pressure (shielding). The superficial and deep veins are connected via perforators, which contain valves allowing flow in the superficial-to-deep direction. The aim of this study is to investigate and quantify the physiological mechanisms of the calf muscle pump, including the effect of venous valves, hydrostatic pressure, and the superficial venous system. Using a one-dimensional pulse wave propagation model, a muscle contraction is simulated by increasing the extravascular pressure in the deep venous segments. The hemodynamics are studied in three different configurations: a single artery-vein configuration with and without valves and a more detailed configuration including a superficial vein. Proximal venous valves increase effective venous return by 53% by preventing reflux. Furthermore, the proximal valves shielding function increases perfusion following contraction. Finally, the superficial system aids in maintaining the perfusion during the contraction phase and reduces the refilling time by 37%. PMID:25766693

  9. Controlling the temperature of bones using pulsed CO2 lasers: observations and mathematical modeling

    PubMed Central

    Lévesque, Luc; Noël, Jean-Marc; Scott, Calum

    2015-01-01

    Temperature of porcine bone specimens are investigated by aiming a pulsed CO2 laser beam at the bone-air surface. This method of controlling temperature is believed to be flexible in medical applications as it avoids the uses of thermal devices, which are often cumbersome and generate rather larger temperature variations with time. The control of temperature using this method is modeled by the heat-conduction equation. In this investigation, it is assumed that the energy delivered by the CO2 laser is confined within a very thin surface layer of roughly 9 μm. It is shown that temperature can be maintained at a steady temperature using a CO2 laser and we demonstrate that the method can be adapted to be used in tandem with another laser beam. This method to control the temperature is believed to be useful in de-contamination of bone during the implantation treatment, in bone augmentation when using natural or synthetic materials and in low-level laser therapy. PMID:26713192

  10. Beverton-Holt discrete pest management models with pulsed chemical control and evolution of pesticide resistance

    NASA Astrophysics Data System (ADS)

    Liang, Juhua; Tang, Sanyi; Cheke, Robert A.

    2016-07-01

    Pest resistance to pesticides is usually managed by switching between different types of pesticides. The optimal switching time, which depends on the dynamics of the pest population and on the evolution of the pesticide resistance, is critical. Here we address how the dynamic complexity of the pest population, the development of resistance and the spraying frequency of pulsed chemical control affect optimal switching strategies given different control aims. To do this, we developed novel discrete pest population growth models with both impulsive chemical control and the evolution of pesticide resistance. Strong and weak threshold conditions which guarantee the extinction of the pest population, based on the threshold values of the analytical formula for the optimal switching time, were derived. Further, we addressed switching strategies in the light of chosen economic injury levels. Moreover, the effects of the complex dynamical behaviour of the pest population on the pesticide switching times were also studied. The pesticide application period, the evolution of pesticide resistance and the dynamic complexity of the pest population may result in complex outbreak patterns, with consequent effects on the pesticide switching strategies.

  11. Computational modeling of stress transient and bubble evolution in short-pulse laser irradiated melanosome particles

    SciTech Connect

    Strauss, M.; Amendt, P.A.; London, R.A.; Maitland, D.J.; Glinsky, M.E.; Lin, C.P.; Kelly, M.W.

    1997-03-04

    Objective is to study retinal injury by subnanosecond laser pulses absorbed in the retinal pigment epithelium (RPE) cells. The absorption centers in the RPE cell are melanosomes of order 1 {mu}m radius. Each melanosome includes many melanin particles of 10-15 nm radius, which are the local absorbers of the laser light and generate a discrete structure of hot spots. This work use the hydrodynamic code LATIS (LAser-TISsue interaction modeling) and a water equation of state to first simulate the small melanin particle of 15 nm responsible for initiating the hot spot and the pressure field. A average melanosome of 1 {mu}m scale is next simulated. Supersonic shocks and fast vapor bubbles are generated in both cases: the melanin scale and the melanosome scale. The hot spot induces a shock wave pressure than with a uniform deposition of laser energy. It is found that an absorption coefficient of 6000 -8000 cm{sup -1} can explain the enhanced shock wave emitted by the melanosome. An experimental and theoretical effort should be considered to identify the mechanism for generating shock wave enhancement.

  12. Acoustic waves generated by pulsed microwaves in viscoelastic rods: modeling and experimental verification.

    PubMed

    Bacon, C; Guilliorit, E; Hosten, B; Chimenti, D E

    2001-09-01

    The acoustic wave generation in a specimen irradiated by a pulsed microwave is predicted theoretically. The specimen is a viscoelastic rod inserted into a wave guide. The model is based on Maxwell's equations, heat equation and thermoviscoelasticity theory. Computations show the presence of temperature oscillations due to the electromagnetic interferences in the irradiated rod if its electromagnetic absorption is low. An experimental method to infer indirectly the detailed behavior of microwave-generated acoustic waves in polymer rods, including the influence of electromagnetic wave reflection at the rod ends, is presented. The method consists of measuring the oscillations in the particle acceleration detected at the end of the rod that are induced by variations in the polymer rod length. The oscillations are caused by changing electromagnetic standing-wave conditions within the rod. It is found that these oscillations are in agreement in period, amplitude, and phase, with independent values of the complex dielectric constant and complex acoustic slowness of the polyvinyl chloride samples used in the study. PMID:11572350

  13. Femoral perfusion after pulsed electromagnetic field stimulation in a steroid-induced osteonecrosis model.

    PubMed

    Ikegami, Akira; Ueshima, Keiichiro; Saito, Masazumi; Ikoma, Kazuya; Fujioka, Mikihiro; Hayashi, Shigeki; Ishida, Masashi; Fujiwara, Hiroyoshi; Mazda, Osam; Kubo, Toshikazu

    2015-07-01

    This study was designed to evaluate femoral perfusion after pulsed electromagnetic field (PEMF) stimulation in a steroid-induced osteonecrosis rabbit model by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Steroid-induced osteonecrosis was produced by single intramuscular injection of methylprednisolone in 15 rabbits. Eight rabbits underwent PEMF stimulation (PEMF group) and seven did not (control group). DCE-MRI was performed before PEMF stimulation, immediately before steroid administration, and 1, 5, 10, and 14 days after steroid administration. Regions of interest were set in the bilateral proximal femora. Enhancement ratio (ER), initial slope (IS), and area under the curve (AUC) were analyzed. ER, IS, and AUC in the control group significantly decreased after steroid administration compared with before administration (P<0.05). In PEMF group, IS significantly decreased; however, ER and AUC showed no significant differences after steroid administration compared with before. ER and IS in PEMF group were higher than in control group until 10th day, and AUC was higher until 5th day after steroid administration (P<0.05). PEMF stimulation restrains the decrease in blood flow after steroid administration. PMID:25808585

  14. Pulsed electromagnetic field treatment enhances healing callus biomechanical properties in an animal model of osteoporotic fracture.

    PubMed

    Androjna, Caroline; Fort, Brian; Zborowski, Maciej; Midura, Ronald J

    2014-09-01

    Delayed bone healing has been noted in osteoporosis patients and in the ovariectomized (OVX) rat model of estrogen-depletion osteopenia. Pulsed electromagnetic field (PEMF) devices are clinically approved as an adjunct to cervical fusion surgery in patients at high risk for non-fusion and for the treatment of fracture non-unions. These bone growth stimulating devices also accelerate the healing of fresh fracture repair in skeletally mature normal rats but have not been tested for efficacy to accelerate and/or enhance the delayed bone repair process in OVX rats. The current study tested the hypothesis that daily PEMF treatments would improve the fracture healing response in skeletally mature OVX rats. By 6 weeks of healing, PEMF treatments resulted in improved hard callus elastic modulus across fibula fractures normalizing the healing process in OVX rats with respect to this mechanical property. Radiographic evidence showed an improved hard callus bridging across fibula fractures in OVX rats treated with PEMF as compared to sham treatments. These findings provide a scientific rationale for investigating whether PEMF might improve bone-healing responses in at-risk osteoporotic patients. PMID:24764277

  15. A 1D pulse wave propagation model of the hemodynamics of calf muscle pump function

    PubMed Central

    Keijsers, J M T; Leguy, C A D; Huberts, W; Narracott, A J; Rittweger, J; van de Vosse, F N

    2015-01-01

    The calf muscle pump is a mechanism which increases venous return and thereby compensates for the fluid shift towards the lower body during standing. During a muscle contraction, the embedded deep veins collapse and venous return increases. In the subsequent relaxation phase, muscle perfusion increases due to increased perfusion pressure, as the proximal venous valves temporarily reduce the distal venous pressure (shielding). The superficial and deep veins are connected via perforators, which contain valves allowing flow in the superficial-to-deep direction. The aim of this study is to investigate and quantify the physiological mechanisms of the calf muscle pump, including the effect of venous valves, hydrostatic pressure, and the superficial venous system. Using a one-dimensional pulse wave propagation model, a muscle contraction is simulated by increasing the extravascular pressure in the deep venous segments. The hemodynamics are studied in three different configurations: a single artery–vein configuration with and without valves and a more detailed configuration including a superficial vein. Proximal venous valves increase effective venous return by 53% by preventing reflux. Furthermore, the proximal valves shielding function increases perfusion following contraction. Finally, the superficial system aids in maintaining the perfusion during the contraction phase and reduces the refilling time by 37%. © 2015 The Authors. International Journal for Numerical Methods in Biomedical Engineering published by John Wiley & Sons Ltd. PMID:25766693

  16. Controlling the temperature of bones using pulsed CO2 lasers: observations and mathematical modeling.

    PubMed

    Lévesque, Luc; Noël, Jean-Marc; Scott, Calum

    2015-12-01

    Temperature of porcine bone specimens are investigated by aiming a pulsed CO2 laser beam at the bone-air surface. This method of controlling temperature is believed to be flexible in medical applications as it avoids the uses of thermal devices, which are often cumbersome and generate rather larger temperature variations with time. The control of temperature using this method is modeled by the heat-conduction equation. In this investigation, it is assumed that the energy delivered by the CO2 laser is confined within a very thin surface layer of roughly 9 μm. It is shown that temperature can be maintained at a steady temperature using a CO2 laser and we demonstrate that the method can be adapted to be used in tandem with another laser beam. This method to control the temperature is believed to be useful in de-contamination of bone during the implantation treatment, in bone augmentation when using natural or synthetic materials and in low-level laser therapy. PMID:26713192

  17. Finite element modeling of ultrasonic waves produced by a pulsed laser

    SciTech Connect

    Dike, J.J.

    1998-03-01

    As part of an effort to apply laser ultrasonics to stress evaluation, sequential thermal and mechanical finite element analyses were used to simulate heating a region of an aluminum surface by a laser pulse and the stress waves that result. As residual or applied stresses can be related to changes in wave velocities, time-of-flight measurements may be used to determine the stresses. The goal of the effort is to improve time-of-flight measurements, and therefore resolution of the calculated stresses, using calculated waveform shapes in model-based signal processing techniques. Detailed finite element simulations of laser ultrasonics may also be used to aid development of techniques that can generate narrow band ultrasound. Because penetration of Rayleigh waves is frequency dependent, they can be used to obtain information about gradients near a surface. If the frequency of the laser generated Rayleigh waves can be controlled, laser ultrasound becomes a more useful tool for examining gradients in material properties or stresses at the surface of a part. Presented here are some preliminary finite element simulations of laser generation of ultrasound waves. Techniques for using commercial finite element codes are discussed and calculated displacement histories are presented for epicentral and same surface locations. These displacement histories are compared with results from the literature.

  18. Comparison of Code Predictions to Test Measurements for Two Orifice Compensated Hydrostatic Bearings at High Reynolds Numbers

    NASA Technical Reports Server (NTRS)

    Keba, John E.

    1996-01-01

    Rotordynamic coefficients obtained from testing two different hydrostatic bearings are compared to values predicted by two different computer programs. The first set of test data is from a relatively long (L/D=1) orifice compensated hydrostatic bearing tested in water by Texas A&M University (TAMU Bearing No.9). The second bearing is a shorter (L/D=.37) bearing and was tested in a lower viscosity fluid by Rocketdyne Division of Rockwell (Rocketdyne 'Generic' Bearing) at similar rotating speeds and pressures. Computed predictions of bearing rotordynamic coefficients were obtained from the cylindrical seal code 'ICYL', one of the industrial seal codes developed for NASA-LeRC by Mechanical Technology Inc., and from the hydrodynamic bearing code 'HYDROPAD'. The comparison highlights the difference the bearing has on the accuracy of the predictions. The TAMU Bearing No. 9 test data is closely matched by the predictions obtained for the HYDROPAD code (except for added mass terms) whereas significant differences exist between the data from the Rocketdyne 'Generic' bearing the code predictions. The results suggest that some aspects of the fluid behavior in the shorter, higher Reynolds Number 'Generic' bearing may not be modeled accurately in the codes. The ICYL code predictions for flowrate and direct stiffness approximately equal those of HYDROPAD. Significant differences in cross-coupled stiffness and the damping terms were obtained relative to HYDROPAD and both sets of test data. Several observations are included concerning application of the ICYL code.

  19. Physical parameters, modeling, and methodological details in using IR laser pulses to warm frozen or vitrified cells ultra-rapidly.

    PubMed

    Kleinhans, F W; Mazur, Peter

    2015-04-01

    We report additional details of the thermal modeling, selection of the laser, and construction of the Cryo Jig used for our ultra-rapid warming studies of mouse oocytes (Jin et al., 2014). A Nd:YAG laser operating at 1064 nm was selected to deliver short 1ms pulses of sufficient power to produce a warming rate of 1×10(7)°C/min from -190°C to 0°C. A special Cryo Jig was designed and built to rapidly remove the sample from LN2 and expose it to the laser pulse. India ink carbon black particles were required to increase the laser energy absorption of the sample. The thermal model reported here is more general than that previously reported. The modeling reveals that the maximum warming rate achievable via external warming across the cell membrane is proportional to (1/R(2)) where R is the cell radius. PMID:25724528

  20. One-dimensional model for the intracranial pulse morphological analysis during hyperventilation and CO2 inhalation tests

    NASA Astrophysics Data System (ADS)

    Ryu, Jaiyoung; Hu, Xiao; Shadden, Shawn C.

    2015-11-01

    The brain's CO2 reactivity mechanism is coupled with cerebral autoregulation and other unique features of cerebral hemodynamics. We developed a one-dimensional nonlinear model of blood flow in the cerebral arteries coupled to lumped parameter (LP) networks. The LP networks incorporate cerebral autoregulation, CO2 reactivity, intracranial pressure, cerebrospinal fluid, and cortical collateral blood flow models. The model was used to evaluate hemodynamic variables (arterial deformation, blood velocity and pressure) in the cerebral vasculature during hyperventilation and CO2 inhalation test. Tests were performed for various arterial blood pressure (ABP) representing normal and hypotensive conditions. The increase of the cerebral blood flow rates agreed well with the published measurements for various ABP measurements taken during clinical CO2 reactivity tests. The changes in distal vasculature affected the reflected pulse wave energy, which caused the waveform morphological changes at the middle cerebral, common and internal carotid arteries. The pulse morphological analysis demonstrated agreement with previous clinical measurements for cerebral vasoconstriction and vasodilation.

  1. New trends in colorectal surgery: single port and natural orifice techniques.

    PubMed

    Daher, Ronald; Chouillard, Elie; Panis, Yves

    2014-12-28

    Single-incision laparoscopic surgery (SILS) and natural orifice transluminal endoscopic surgery (NOTES) have rapidly gained pace worldwide, potentially replacing conventional laparoscopic surgery (CLS) as the preferred colorectal surgery technique. Currently available data mainly consist of retrospective series analyzed in four meta-analyses. Despite conflicting results and lack of an objective comparison, SILS appears to offer cosmetic advantages over CLS. However, due to conflicting results and marked heterogeneity, present data fail to show significant differences in terms of operative time, postoperative morbidity profiles, port-site complications rates, oncological appropriateness, duration of hospitalization or cost when comparing SILS with conventional laparoscopy for colorectal procedures. The application of "pure" NOTES in humans remains limited to case reports because of unresolved issues concerning the ideal access site, distant organ reach, spatial orientation and viscera closure. Alternatively, minilaparoscopy-assisted natural orifice surgery techniques are being developed. The transanal "down-to-up" total mesorectum excision has been derived for transanal endoscopic microsurgery (TEM) and represents the most encouraging NOTES-derived technique. Preliminary experiences demonstrate good oncological and functional short-term outcomes. Large-scale randomized controlled trials are now mandatory to confirm the long-term SILS results and validate transanal TEM for the application of NOTES in humans. PMID:25561780

  2. Effect of noncircular orifice plates on the near flow field of turbulent free jets

    NASA Astrophysics Data System (ADS)

    Xu, Min-Yi; Tong, Xing-Qing; Yue, Dan-Ting; Zhang, Jian-Peng; Mi, Jian-Chun; Nathan, G. J.; Kalt, P. A. M.

    2014-12-01

    In this paper, we experimentally investigate the near-field flow characteristics of turbulent free jets respectively issued from circular, triangular, diamond, rectangular, and notched-rectangular orifice plates into air surroundings. All the orifice plates have identical opening areas or equivalent diameters (De) and their aspect ratios (AR) range from 1 to 6.5. Planar particle image velocimetry (PIV) is used to measure the velocity field at the same Reynolds number of Re = 5 × 104, where Re = UeDe/v with Ue being the exit bulk velocity and v the kinematic viscosity of fluid. The mean and turbulent velocity fields of all the five jets are compared in detail. Results show that the noncircular jets can enhance the entrainment rate, reflected by the higher acceleration rates of mean velocity decay and spread, shorten the length of the unmixed core, expedite the increase of turbulent intensity compared with the circular counterpart shortened unmixed core, and increase turbulent intensity comparing to the circular counterpart. Among the five jets, the rectangular jet (AR = 6.5) produces the greatest decay rate of the near-field mean velocity, postpones the position at which the `axis-switching' phenomenon occurs. This supports that axis switching phenomenon strongly depends on jet initial conditions. In addition, the hump in the centerline variation of the turbulence intensity is observed in the rectangular and triangular jets, but not in the circular jet, nor in diamond jet nor in notched-rectangular jet.

  3. New trends in colorectal surgery: Single port and natural orifice techniques

    PubMed Central

    Daher, Ronald; Chouillard, Elie; Panis, Yves

    2014-01-01

    Single-incision laparoscopic surgery (SILS) and natural orifice transluminal endoscopic surgery (NOTES) have rapidly gained pace worldwide, potentially replacing conventional laparoscopic surgery (CLS) as the preferred colorectal surgery technique. Currently available data mainly consist of retrospective series analyzed in four meta-analyses. Despite conflicting results and lack of an objective comparison, SILS appears to offer cosmetic advantages over CLS. However, due to conflicting results and marked heterogeneity, present data fail to show significant differences in terms of operative time, postoperative morbidity profiles, port-site complications rates, oncological appropriateness, duration of hospitalization or cost when comparing SILS with conventional laparoscopy for colorectal procedures. The application of “pure” NOTES in humans remains limited to case reports because of unresolved issues concerning the ideal access site, distant organ reach, spatial orientation and viscera closure. Alternatively, minilaparoscopy-assisted natural orifice surgery techniques are being developed. The transanal “down-to-up” total mesorectum excision has been derived for transanal endoscopic microsurgery (TEM) and represents the most encouraging NOTES-derived technique. Preliminary experiences demonstrate good oncological and functional short-term outcomes. Large-scale randomized controlled trials are now mandatory to confirm the long-term SILS results and validate transanal TEM for the application of NOTES in humans. PMID:25561780

  4. Orifice-assisted small-incision surgery: case series in benign and oncologic gynecology.

    PubMed

    Einarsson, Jon I; Cohen, Sarah L; Puntambekar, Shailesh

    2012-01-01

    This case series describes the feasibility of orifice-assisted small-incision surgery (OASIS), a novel technique that may incorporate benefits of single-incision and natural-orifice surgery while minimizing issues such as instrument crowding and interaction of optical access with operative instrumentation. In our multiple-site series, we included patients from a large academic medical center in the northeastern United States and a private gynecology clinic in India. Between the 2 centers, a total of 14 patients (5 with benign disease and 9 with oncologic disease) underwent the following procedures: OASIS total laparoscopic hysterectomy, laparoscopic supracervical hysterectomy, laparoscopic myomectomy, or laparoscopic radical hysterectomy with pelvic lymph node dissection. The initial 14 cases were safely completed. Oncologic clearance was consistent with specialty norms. Operating time ranged from 60 to 150 minutes, and estimated blood loss ranged from 10 to 500 mL. Detailed procedure descriptions and videos are provided. Based on preliminary case series experience, OASIS seems to be a safe and feasible addition to the advanced minimally invasive surgeons' armamentarium for both benign and oncologic cases. PMID:22417906

  5. Atomistic Computational Model of Radiation Damage of Nano-sized Systems in Intense X-ray Pulses

    NASA Astrophysics Data System (ADS)

    Ho, Phay; Jiang, Wei; Lau, Kar Chun; Young, Linda

    2014-05-01

    We present a combined Monte-Carlo/molecular- dynamics (MC/MD) computational model that is suitable for monitoring the physics of intense, femtosecond XFEL pulses interacting with complex systems of various sizes, from nanometers to micrometers, and matters of various compositions. In this model, the occurrences of x-ray absorption, ionization, relaxation and electron-impact processes are treated by a MC method, and the subsequent dynamics of the all the electrons, ions and atoms are tracked using an MD method. Our model extends the previous MC/MD model and provides new capabilities to probe the impacts of transient states on radiation damage dynamics. Recently, we have added LAMMPS as the driver of MD dynamics. This is a critical addition as now our code can run on Mira, a new petascale supercomputer with 786K core processors at the Argonne Leadership Computing Facility. Also, it can treat micron-sized systems with trillions of particles and both homogeneous and heterogeneous composition. Using our model, we examine the ionization dynamics of Argon clusters in an XFEL pulse as a function of particle sizes and pulse parameters, and we compare our results with the experimental data. Supported by the Chemical Sciences, Geosciences, and Biosciences Di- vision, Office of Basic Energy Sciences, Office of Science, US Dept of Energy, Contract DE-AC02-06CH11357.

  6. Multi-Pulse laser ablation modeling with applications to automated zona removal.

    PubMed

    Wong, Christopher Yee; Mills, James K

    2015-08-01

    Laser zona drilling (LZD), the ablation of a portion of the zona pellucida (ZP) in embryos with the use of a laser, is a required step in many embryonic surgical procedures such as assisted hatching and preimplantation genetic diagnosis. The objective of LZD is to remove specific locations of the ZP while minimizing potential harmful thermal effects to important structures of the embryo, namely the blastomeres. Current thermal analyzes of lasers used in LZD only encompass the use of a single pulse, whereas LZD is typically performed using multiple pulses. In this paper we analyze the effect of multipulse LZD and introduce a linear approximation method for multi-pulse LZD. Furthermore, we describe a novel method of measuring the thermal effect of a single laser pulse using the thermosensitive fluorescent dye Rhodamine B and a high speed camera. PMID:26736816

  7. Computer modeling of electrical and thermal performance during bipolar pulsed radiofrequency for pain relief

    SciTech Connect

    Pérez, Juan J.; Pérez-Cajaraville, Juan J.; Muñoz, Víctor; Berjano, Enrique

    2014-07-15

    Purpose: Pulsed RF (PRF) is a nonablative technique for treating neuropathic pain. Bipolar PRF application is currently aimed at creating a “strip lesion” to connect the electrode tips; however, the electrical and thermal performance during bipolar PRF is currently unknown. The objective of this paper was to study the temperature and electric field distributions during bipolar PRF. Methods: The authors developed computer models to study temperature and electric field distributions during bipolar PRF and to assess the possible ablative thermal effect caused by the accumulated temperature spikes, along with any possible electroporation effects caused by the electrical field. The authors also modeled the bipolar ablative mode, known as bipolar Continuous Radiofrequency (CRF), in order to compare both techniques. Results: There were important differences between CRF and PRF in terms of electrical and thermal performance. In bipolar CRF: (1) the initial temperature of the tissue impacts on temperature progress and hence on the thermal lesion dimension; and (2) at 37 °C, 6-min of bipolar CRF creates a strip thermal lesion between the electrodes when these are separated by a distance of up to 20 mm. In bipolar PRF: (1) an interelectrode distance shorter than 5 mm produces thermal damage (i.e., ablative effect) in the intervening tissue after 6 min of bipolar RF; and (2) the possible electroporation effect (electric fields higher than 150 kV m{sup −1}) would be exclusively circumscribed to a very small zone of tissue around the electrode tip. Conclusions: The results suggest that (1) the clinical parameters considered to be suitable for bipolar CRF should not necessarily be considered valid for bipolar PRF, and vice versa; and (2) the ablative effect of the CRF mode is mainly due to its much greater level of delivered energy than is the case in PRF, and therefore at same applied energy levels, CRF, and PRF are expected to result in same outcomes in terms of

  8. Numerical Modeling and Testing of an Inductively-Driven and High-Energy Pulsed Plasma Thrusters

    NASA Technical Reports Server (NTRS)

    Parma, Brian

    2004-01-01

    Pulsed Plasma Thrusters (PPTs) are advanced electric space propulsion devices that are characterized by simplicity and robustness. They suffer, however, from low thrust efficiencies. This summer, two approaches to improve the thrust efficiency of PPTs will be investigated through both numerical modeling and experimental testing. The first approach, an inductively-driven PPT, uses a double-ignition circuit to fire two PPTs in succession. This effectively changes the PPTs configuration from an LRC circuit to an LR circuit. The LR circuit is expected to provide better impedance matching and improving the efficiency of the energy transfer to the plasma. An added benefit of the LR circuit is an exponential decay of the current, whereas a traditional PPT s under damped LRC circuit experiences the characteristic "ringing" of its current. The exponential decay may provide improved lifetime and sustained electromagnetic acceleration. The second approach, a high-energy PPT, is a traditional PPT with a variable size capacitor bank. This PPT will be simulated and tested at energy levels between 100 and 450 joules in order to investigate the relationship between efficiency and energy level. Arbitrary Coordinate Hydromagnetic (MACH2) code is used. The MACH2 code, designed by the Center for Plasma Theory and Computation at the Air Force Research Laboratory, has been used to gain insight into a variety of plasma problems, including electric plasma thrusters. The goals for this summer include numerical predictions of performance for both the inductively-driven PPT and high-energy PFT, experimental validation of the numerical models, and numerical optimization of the designs. These goals will be met through numerical and experimental investigation of the PPTs current waveforms, mass loss (or ablation), and impulse bit characteristics.

  9. Hybrid Natural Orifice Transluminal Endoscopic Surgery with Sentinel Lymph Node Navigation for Deep Early Gastric Cancer in the Fundic Region

    PubMed Central

    Park, Yoon Suk; Kim, Seong Hwan; Ryu, Hee Yun; Cho, Young Kwan; Jo, Yun Ju; Son, Tae il; Hong, Young Ok

    2016-01-01

    For patients refusing surgical treatment for deep early gastric cancer, hybrid natural orifice transluminal endoscopic surgery with sentinel lymph node navigation is a potential treatment option, particularly when the anatomic location of the cancer has low probability of lymph node metastasis. We report a case of deep early gastric cancer of the fundus beyond the endoscopic submucosal dissection indication that was treated by hybrid natural orifice transluminal endoscopic surgery with sentinel lymph node navigation. In a conventional approach, a total gastrectomy would have been needed; however, the patient refused surgical intervention. In this case, since the patient showed no positivity of the sentinel lymph node on intraoperative navigation, laparoscopic basin lymph node dissection was not performed. Hybrid natural orifice transluminal endoscopic surgery might be considered for specific regions such as the safety zone where lymph node metastases are less likely to occur. PMID:27020308

  10. Integrating the pulse of the riverscape and landscape: modelling stream metabolism using continuous dissolved oxygen measurements

    NASA Astrophysics Data System (ADS)

    Soulsby, C.; Birkel, C.; Malcolm, I.; Tetzlaff, D.

    2013-12-01

    Stream metabolism is a fundamental pulse of the watershed which reflects both the in-stream environment and its connectivity with the wider landscape. We used high quality, continuous (15 minute), long-term (>3 years) measurement of stream dissolved oxygen (DO) concentrations to estimate photosynthetic productivity (P) and system respiration (R) in forest and moorland reaches of an upland stream with peaty soils. We calibrated a simple five parameter numerical oxygen mass balance model driven by radiation, stream and air temperature, stream depth and re-aeration capacity. This used continuous 24-hour periods for the whole time series to identify behavioural simulations where DO simulations were re-produced sufficiently well to be considered reasonable representations of ecosystem functioning. Results were evaluated using a seasonal Regional Sensitivity Analysis and a co-linearity index for parameter sensitivity. This showed that >95 % of the behavioural models for the moorland and forest sites were identifiable and able to infer in-stream processes from the DO time series for almost half of all measured days at both sites. Days when the model failed to simulate DO levels successfully provided invaluable insight into time periods when other factors are likely to disrupt in-stream metabolic processes; these include (a) flood events when scour reduces the biomass of benthic primary producers, (b) periods of high water colour in higher summer/autumn flows and (c) low flow periods when hyporheic respiration is evident. Monthly P/R ratios <1 indicate a heterotrophic system with both sites exhibiting similar temporal patterns; with a maximum in February and a second peak during summer months. However, the estimated net ecosystem productivity (NPP) suggests that the moorland reach without riparian tree cover is likely to be a much larger source of carbon to the atmosphere (122 mmol C m-2 d-1) compared to the forested reach (64 mmol C m-2 d-1). The study indicates the value

  11. Downscaling transient climate change using a Neyman-Scott Rectangular Pulses stochastic rainfall model

    NASA Astrophysics Data System (ADS)

    Burton, A.; Fowler, H. J.; Blenkinsop, S.; Kilsby, C. G.

    2010-02-01

    SummaryThe future management of hydrological systems must be informed by climate change projections at relevant time horizons and at appropriate spatial scales. Furthermore, the robustness of such management decisions is dependent on both the uncertainty inherent in future climate change scenarios and the natural climate system. Addressing these needs, we present a new transient rainfall simulation methodology which combines dynamical and statistical downscaling techniques to produce transient (i.e. temporally non-stationary) climate change scenarios. This is used to generate a transient multi-model ensemble of simulated point-scale rainfall time series for 1997-2085 for the polluted Brévilles spring in Northern France. The recovery of this previously potable source may be affected by climatic changes and variability over the next few decades. The provision of locally-relevant transient climate change scenarios for use as input to hydrological models of both water quality and quantity will ultimately provide a valuable resource for planning and decision making. Observed rainfall from 1988-2006 was characterised in terms of a set of statistics for each calendar month: the daily mean, variance, probability dry, lag-1 autocorrelation and skew, and the monthly variance. The Neyman-Scott Rectangular Pulses (NSRP) stochastic rainfall model was fitted to these observed statistics and correctly simulated both monthly statistics and extreme rainfall properties. Multiplicative change factors which quantify the change in each statistic between the periods 1961-1990 and 2071-2100 were estimated for each month and for each of 13 Regional Climate Models (RCMs) from the PRUDENCE ensemble. To produce transient climate change scenarios, pattern scaling factors were estimated and interpolated from four time-slice integrations of two General Circulation Models which condition the RCMs, ECHAM4/OPYC and HadCM3. Applying both factors to the observed statistics provided projected

  12. A Superfluid Pulse Tube Refrigerator Without Moving Parts for Sub-Kelvin Cooling

    NASA Technical Reports Server (NTRS)

    Miller, Franklin K.

    2012-01-01

    A report describes a pulse tube refrigerator that uses a mixture of He-3 and superfluid He-4 to cool to temperatures below 300 mK, while rejecting heat at temperatures up to 1.7 K. The refrigerator is driven by a novel thermodynamically reversible pump that is capable of pumping the He-3 He-4 mixture without the need for moving parts. The refrigerator consists of a reversible thermal magnetic pump module, two warm heat exchangers, a recuperative heat exchanger, two cold heat exchangers, two pulse tubes, and an orifice. It is two superfluid pulse tubes that run 180 out of phase. All components of this machine except the reversible thermal pump have been demonstrated at least as proof-of-concept physical models in previous superfluid Stirling cycle machines. The pump consists of two canisters packed with pieces of gadolinium gallium garnet (GGG). The canisters are connected by a superleak (a porous piece of VYCOR glass). A superconducting magnetic coil surrounds each of the canisters.

  13. Investigations of Acoustics and Heat Transfer Characteristics of Thermoacoustic Driven Pulse Tube Refrigerators

    NASA Astrophysics Data System (ADS)

    Bretagne, E.; François, M.-X.; Ishikawa, H.

    2004-06-01

    The purpose of this article is to investigate the design of the ThermoAcoustic Driven Pulse Tube Refrigerator which is a promising solution for large scale pulse tube applications. Designing concepts and preliminary studies of heat transfer in heat exchangers specifically for large scale TADPTR are presented. Thus, we introduce the way to deal with different components of the Pulse Tube Refrigerator to achieve the most efficient regenerator operation with the constraints imposed by the thermoacoustic driver. The main building-concepts are illustrated by considering the combinations of a standing wave Thermoacoustic prime mover with (i) an Inertance-Orifice PTR and (ii) a Lumped Boost PTR. Both experimental and numerical results support the models. Furthermore, we investigate the heat transfer mechanism for Reynolds number between 104 to 2×105 in helium. For the current experiment, measurements are taken at the cold heat exchanger of the prime mover. For the purpose of the analysis we select testing conditions so that the particle displacement is larger than the heat exchanger length and the boundary layer assumption applies. Adequacy of the steady flow assumption is discussed. Nusselt number obtained from the measurements is then correlated with a function of Prandtl, Reynolds and Valensi numbers.

  14. Pulse wave analysis in a 180-degree curved artery model: Implications under physiological and non-physiological inflows

    NASA Astrophysics Data System (ADS)

    Bulusu, Kartik V.; Plesniak, Michael W.

    2013-11-01

    Systolic and diastolic blood pressures, pulse pressures, and left ventricular hypertrophy contribute to cardiovascular risks. Increase of arterial stiffness due to aging and hypertension is an important factor in cardiovascular, chronic kidney and end-stage-renal-diseases. Pulse wave analysis (PWA) based on arterial pressure wave characteristics, is well established in clinical practice for evaluation of arterial distensibility and hypertension. The objective of our exploratory study in a rigid 180-degree curved artery model was to evaluate arterial pressure waveforms. Bend upstream conditions were measured using a two-component, two-dimensional, particle image velocimeter (2C-2D PIV). An ultrasonic transit-time flow meter and a catheter with a MEMS-based solid state pressure sensor, capable of measuring up to 20 harmonics of the observed pressure waveform, monitored flow conditions downstream of the bend. Our novel continuous wavelet transform algorithm (PIVlet 1.2), in addition to detecting coherent secondary flow structures is used to evaluate arterial pulse wave characteristics subjected to physiological and non-physiological inflows. Results of this study will elucidate the utility of wavelet transforms in arterial function evaluation and pulse wave speed. Supported by NSF Grant No. CBET- 0828903 and GW Center for Biomimetics and Bioinspired Engineering.

  15. Spatio-temporal modeling and optimization of a deformable-grating compressor for short high-energy laser pulses.

    PubMed

    Qiao, J; Papa, J; Liu, X

    2015-10-01

    Monolithic large-scale diffraction gratings are desired to improve the performance of high-energy laser systems and scale them to higher energy, but the surface deformation of these diffraction gratings induce spatio-temporal coupling that is detrimental to the focusability and compressibility of the output pulse. A new deformable-grating-based pulse compressor architecture with optimized actuator positions has been designed to correct the spatial and temporal aberrations induced by grating wavefront errors. An integrated optical model has been built to analyze the effect of grating wavefront errors on the spatio-temporal performance of a compressor based on four deformable gratings. A 1.5-meter deformable grating has been optimized using an integrated finite-element-analysis and genetic-optimization model, leading to spatio-temporal performance similar to the baseline design with ideal gratings. PMID:26480107

  16. On a Fitzhugh-Nagumo type model for the pulse-like jasmonate defense response in plants.

    PubMed

    Chiangga, S; Pornkaveerat, W; Frank, T D

    2016-03-01

    A mechanistic model of the Fitzhugh-Nagumo type is proposed for the pulse-like jasmonate response in plants. The model is composed of a bistable signaling pathway coupled to a negative feedback loop. The bistable signaling pathway describes a recently discovered positive feedback loop involving jasmonate and the MYC2 transcription factor regulating promoter activity during plant defense. The negative feedback loop is assumed to reflect a second jasmonate-dependent signaling pathway that is also used for ethylene signaling. The impact of the negative feedback loop is to destroy the high-level jasmonate fixed-point of the bistable jasmonate/MYC2 module. As a result, the high-level state becomes a ghost attractor and the jasmonate defense response becomes pulse-like. PMID:26774970

  17. Noncircular Orifice Holes and Advanced Fabrication Techniques for Liquid Rocket Injectors (Phases 1, 2, 3, and 4)

    NASA Technical Reports Server (NTRS)

    Mchale, R. M.; Nurick, W. H.

    1974-01-01

    A comprehensive summary of the results of a cold-flow and hot-fire experimental study of the mixing and atomization characteristics of injector elements incorporating noncircular orifices is presented. Both liquid/liquid and gas/liquid element types are discussed. Unlike doublet and triplet elements (circular orifices only) were investigated for the liquid/liquid case while concentric tube elements were investigated for the gas/liquid case. It is concluded that noncircular shape can be employed to significant advantage in injector design for liquid rocket engines.

  18. Does Low-intensity pulsed ultrasound treatment repair articular cartilage injury? A rabbit model study

    PubMed Central

    2014-01-01

    Background Low-intensity pulsed ultrasound (LIPUS) regiment has been used to treat fractures with non-union and to promote bone union in general. The effect of LIPUS on articular cartilage metabolism has been characterized. Yet, the effect of LIPUS to repair articular cartilage injury remains unclear in vivo. Methods We designed a study to investigate the effect of LIPUS on articular cartilage repairing in a rabbit severe cartilage injury model. Eighteen rabbits were divided into three groups: Sham-operated group, operated group without-LIPUS-treatment, operated group with-LIPUS-treatment (a daily 20-minute treatment for 3 months). Full-thickness cartilage defects were surgically created on the right side distal femoral condyle without intending to penetrate into the subchondral bone, which mimicked severe chondral injury. MR images for experimental joints, morphology grading scale, and histopathological Mankin score were evaluated. Results The preliminary results showed that the operated groups with-LIPUS-treatment and without-LIPUS-treatment had significantly higher Mankin score and morphological grading scale compared with the sham-operated group. However, there was no significant difference between the with-LIPUS-treatment and without-LIPUS-treatment groups. Cartilage defects filled with proliferative tissue were observed in the with-LIPUS-treatment group grossly and under MR images, however which presented less up-take under Alcian blue stain. Furthermore, no new deposition of type II collagen or proliferation of chondrocyte was observed over the cartilage defect after LIPUS treatment. Conclusion LIPUS has no significant therapeutic potential in treating severe articular cartilage injury in our animal study. PMID:24507771

  19. Modeling of the nanoparticle coagulation in pulsed radio-frequency capacitively coupled C2H2 discharges

    NASA Astrophysics Data System (ADS)

    Liu, Xiang-Mei; Li, Qi-Nan; Li, Rui

    2015-07-01

    The role of pulse parameters on nanoparticle property is investigated self-consistently based on a couple of fluid model and aerosol dynamics model in a capacitively coupled parallel-plate acetylene (C2H2) discharge. In this model, the mass continuity equation, momentum balance equation, and energy balance equation for neutral gas are taken into account. Thus, the thermophoretic force arises when a gas temperature gradient exists. The typical results of this model are positive and negative ion densities, electron impact collisions rates, nanoparticle density, and charge distributions. The simulation is performed for duty ratio 0.4/0.7/1.0, as well as pulse modulation frequency from 40 kHz to 2.7 MHz for pure C2H2 discharges at a pressure of 500 mTorr. We find that the pulse parameters, especially the duty ratio, have a great affect on the dissociative attachment coefficient and the negative density. More importantly, by decreasing the duty ratio, nanoparticles start to diffuse to the wall. Under the action of gas flow, nanoparticle density peak is created in front of the pulse electrode, where the gas temperature is smaller. Project supported by the Natural Science Foundation of Heilongjiang Province, China (Grant Nos. A2015011 and A2015010), the Postdoctoral Scientific Research Developmental Fund of Heilongjiang Province, China (Grant No. LBH-Q14159), the National Natural Science Foundation of China (Grant No. 11404180), and the Program for Young Teachers Scientific Research in Qiqihar University, China (Grant No. 2014k-Z11).

  20. Modeling target bulk heating resulting from ultra-intense short pulse laser irradiation of solid density targets

    SciTech Connect

    Antici, P.; INRS-EMT, Varennes, Québec; Istituto Nazionale di Fisica Nucleare, Via E. Fermi, 40-00044 Frascati; LULI, École Polytechnique, CNRS, CEA, UPMC, route de Saclay, 91128 Palaiseau ; Gremillet, L.; Grismayer, T.; Audebert, P.; Mančic, A.; Fuchs, J.; Borghesi, M.; Cecchetti, C. A.

    2013-12-15

    Isochoric heating of solid-density matter up to a few tens of eV is of interest for investigating astrophysical or inertial fusion scenarios. Such ultra-fast heating can be achieved via the energy deposition of short-pulse laser generated electrons. Here, we report on experimental measurements of this process by means of time- and space-resolved optical interferometry. Our results are found in reasonable agreement with a simple numerical model of fast electron-induced heating.