bluuebunny/crossref_metadata_2025 huggingface dataset:
Appraisal of Universal Wake Numbers From Data for Roughened Circular Cylinders
Authors: Buresti G.
Published: October 2009

An analysis was carried out to check whether certain existing universal wake numbers can characterize the cross-flow around roughened circular cylinders in transitional regimes. The results confirmed the soundness of the idea of the existence of a link between the drag coefficient of a bluff body, its pressure distribution, and the frequency of the shedding of vortices in its wake. In particular, Bearman’s number and Griffin’s number were shown to be able to describe this link with sufficient accuracy and to be a function of the Reynolds number based on the typical dimension of the surface roughness. A physical interpretation of Griffin’s number was also given which permits to link the drag force with the velocity of the potential flow at separation and the frequency of vortex shedding.
Correspondent Report on the Initial Meeting, Held September 3–6, 1980, of the 1980–1981 AFOSR-HTTM-Stanford Conference on Complex Turbulent Flows: Comparison of Computation and Experiment
Authors: Kline S. J. , Lilley G. M.
Published: October 2009

The first of two meetings of the 1980–1981 AFOSR-HTTM-Stanford Conference on Complex Turbulent Flows: Comparison of Computation and Experiment is described. The Conference is a cooperative research effort involving a major fraction of research workers in turbulent flow. It has three objectives: (i) establishment of trustworthy data sets that can be used as the basis for modeling complex turbulent flows and as standard trial cases for checking output of computations in such flows; (ii) the creation of a data library in standardized, machine-readable form on magnetic tape of the trustworthy cases; (iii) the comparison of current computational output from many groups with the standard trial cases. The meeting on data held at Stanford University, Sept. 3–5, 1980, is described in this paper, including: a short history of the problem, difficulties in turbulence research and recordation of adequate data sets, organization and special procedures in the conference, the trial cases established for the 1981 meeting on computation, a number of other specific results from the meeting, and conclusions. It is concluded that the 1980 meeting was successful not only in meeting goals (i) and (ii) but also in clarifying many other issues that have been troubling the research community and clarifying needs for future researches. The Proceedings from the 1980 meeting will be published in spring, 1981 and may be ordered from the first author.
The Effect of Gravity on Certain Curved Channel Potential Flows
Authors: Chow W. L. , Chan P. C. T.
Published: October 2009

It is shown that the method of hodograph transformation coupled with numerical calculations can be an effective method to account for the effect of gravity on certain two-dimensional potential flow problems. Specifically, the problem of a horizontal channel flow discharging an incompressible fluid through a circular-arc contraction has been worked out to illustrate the procedure. The upstream approaching flow conditions, the opening height, and also the downstream free surface flow must be compatible with each other. They must be determined through iterations. The method of iteration is also presented and discussed.
Preston Tube Calibrations and Direct Force Floating Element Measurements in a Two-Dimensional Turbulent Boundary Layer
Authors: McAllister J. E. , Pierce F. J. , Tennant M. H.
Published: October 2009

Preston tubes provide a convenient means of estimating local wall shear stress. Practical difficulties arise from a lack of calibration data obtained in turbulent boundary layer flows and from the wide choice of calibration equations available mainly from pipe flow calibrations. The results of an experimental study comparing a large number of direct force local wall shear stress measurements in a near-zero pressure gradient two-dimensional turbulent boundary layer flow are presented. The results indicate that there is consistent and excellent agreement between the Patel intermediate calibration formula and the direct force measurements. Typical differences among the direct force measurements and several other proposed calibration equations are also shown.
Scaling Parameters for a Time-Averaged Separation Bubble
Authors: Smits A. J.
Published: October 2009

A splitter plate is placed in the wake of a two-dimensional bluff body. The splitter plate is long enough for the separated flow behind the body to reattach on the splitter plate. The time-averaged properties of this “closed” separation bubble are investigated under a wide range of kinematic conditions. It is found that blockage reduces the base pressure coefficient (Cpb) and the distance to reattachment (l) but the relationship between l and Cpb is not obvious. The pressure distribution in the separated zone, scaled on Cpb and l, can be described by a universal curve. The usefulness of a slotted wall in reducing blockage effects on bluff body flows is shown to be limited in that the wall porosity affects only some properties of the separation bubble.
Observations and Measurements of Flow in a Partially-Filled Horizontally Rotating Cylinder
Authors: Gans R. F. , Yalisove S. M.
Published: October 2009

The authors report measurements of azimuthal velocity versus radius in a partially-filled horizontally rotating cylinder. These data confirm theoretical calculations for laminar flow. Three nonlaminar flow states are described and a map shows boundaries separating the laminar state, and two of the nonlaminar states, in a two parameter space.
Flow Aerodynamics Modeling of an MHD Swirl Combustor: Calculations and Experimental Verification
Authors: Gupta A. K. , Bee´r J. M. , Louis J. F. , Busnaina A. A. , Lilley D. G.
Published: October 2009

This paper describes a computer code for calculating the flow dynamics of constant density flow in the second stage trumpet shaped nozzle section of a two stage MHD swirl combustor for application to a disk generator. The primitive pressure-velocity variable, finite difference computer code has been developed to allow the computation of inert nonreacting turbulent swirling flows in an axisymmetric MHD model swirl combustor. The method and program involve a staggered grid system for axial and radial velocities, and a line relaxation technique for efficient solution of the equations. Turbulence simulation is by way of a two-equation κ-ε model. The code produces as output the flowfield map of the nondimensional stream function, axial, and swirl velocity. Good argeement was obtained between the theoretical predictions and the qualitative experimental results. The best seed injector location for uniform seed distribution at combustor exit is with injector located centrally on the combustor axis at entrance to the second stage combustor.
A Set of Instruments Useful for Liquid Quality Control During Cavitation Research
Authors: Oldenziel D. M.
Published: October 2009

It is well-accepted by investigators of cavitation phenomena that undissolved and dissolved gas content in the liquid used affect the onset and type of cavitation in many cases. That is why not only cavitation studies have been carried out to understand the hydrodynamic properties and interactions but also to get insight into the relations between cavitation and liquid quality. The liquid quality is a criterion which gives information about the dissolved gas content and about the undissolved gas content in terms of size distribution and concentration of bubbles and gas pockets dispersed in the liquid. Although not every detail of the interaction between cavitation (inception) and liquid quality is known, it is at least necessary to control and to know the liquid quality. In this way experiments become repeatable and the investigator is allowed to focus his attention to hydrodynamical questions only. In this paper some new and modified instruments and control systems in respect to liquid quality are described. They are an automatic dissolved air (gas) content meter, an acoustic doppler system for bubble detection and a bubble filter for injection of a known bubble mixture.
A Controlled Buoyant Jet for Enhancing Stratification in a Liquid Storage Tank
Authors: Gari H. N. , Loehrke R. I.
Published: October 2009

An inlet manifold is described for introducing liquid of arbitrary temperature into a tank without destroying pre-existing stratification. This manifold may be described as a controlled, buoyant jet. A one-dimensional, analytical model of the manifold is developed. The predictions of this model are compared in a qualitative sense, with the results of flow visualization experiments. Quantitative comparisons are also made with the results of thermal tests of the major components of the manifold.
A Study of the Measurement of Cavitation Inception Using an Electrostatic Technique
Authors: Yuecan Tan , Velkoff H. R.
Published: October 2009

A new concept for detecting cavitation inception has been studied experimentally. In this exploratory study, cavitation is generated by varying the flow velocity and pressure around a circular cylinder. Cavitation inception has been detected by sensing the natural charges and electrification generated during cavitation. The agreement between visual determination and detection using electrostatic probes was quite good. The background and possible mechanisms are reviewed and discussed.
Turbulent Air Flow Over Rough Surfaces: II. Turbulent Flow Parameters
Authors: Nourmohammadi Khosrow , Hopke P. K. , Stukel J. J.
Published: October 2009

The objective of the present study was to examine experimentally the turbulent flow structure in a repeated rib geometry rough wall surface as a function of the ratio of the roughness height to the pipe diameter (K/D), the ratio of the spacing between the elements to the roughness height (P/K), the axial position within a rib cycle, and the Reynolds number. For small P/K values, the turbulent intensities and Reynolds shear stress variations were similar to those found for smooth wall pipe flow. Unique relationships for the u′ and v′ were found that were valid in the outer layer of the flow for all axial positions and all values of P/K and K/D.
Flow in an Open Tank With a Free Surface Driven by the Spinning Bottom
Authors: Hyun Jae Min
Published: October 2009

An investigation is made of flows of a viscous incompressible fluid inside a circular cylindrical tank. The flow is driven by the spinning bottom endwall disk of the tank. Numerical solutions of the Navier-Stokes equations were obtained over a range of rotational Reynolds number and of aspect ratio (cylinder height/radius) using two kinds of boundary condition at the top: a closed tank with a rigid lid and an open tank with a free surface. We provide descriptions of flow details for these two boundary conditions at the top. For small aspect ratios, the nature of the azimuthal flow is distinctly different depending on the type of the top boundary condition, i.e., a Couette flow under a rigid lid and a solid-body rotation under a free surface. These qualitative flow patterns are insensitive to the Reynolds number. For flows with a finite aspect ratio and at small Reynolds numbers, the change in the top boundary condition has little impact on the flow. For flows with a finite aspect ratio and at large Reynolds numbers, the prevailing flow patterns are of boundary layer-type. At a given vertical level, the angular velocity attains a larger value under a free surface than under a rigid lid.
The Use of the Dye-Layer Technique for Unsteady Flow Visualization
Authors: Gad-el-Hak Mohamed
Published: October 2009

The unsteady flow around three-dimensional lifting surfaces undergoing a harmonic pitching motion was studied in a towing tank using the dye-layer technique. Different color fluorescent dyes were placed in the flow field by laying several thin, horizontal sheets prior to towing the lifting surface. The fluorescent dyes were excited using a sheet of laser light projected in the desired plane. The technique allowed the visualization of the flow in the separation zone on the low-pressure side of the lifting surface, the flow in the wake region, and the potential flow away from the surface. The complex unsteady flow structures were gleaned from observing the visualization results recorded on cine´ films.
A Study of the Internal Forces in a Variable-Displacement Vane-Pump—Part II: A Parametric Study
Authors: Karmel A. M.
Published: October 2009

This is the second part of an analytical study of the internal forces in a variable-displacement vane-pump. It presents a parametric study of the forces and torques applied to the mechanism and the shaft of this pump, as functions of line pressure, the eccentricity, and the design geometry. It is shown that the continuous components of the torque and of the direction of the radial shaft-load vary as a sawtooth wave at twice the vane-frequency while the magnitude of the radial shaft-load varies as a square wave at vane-frequency. The design criterion developed in the first part of this study is used to demonstrate the elimination of the magnitude variations in the radial shaft-load. The intermittent components of the internal forces vary as a pulse train at vane frequency and may produce high-peak pressure pulses which must be closely controlled. The variable-capacity feature of variable-displacement vane-pumps has a significant effect on the torque applied to the mechanism, but only a secondary effect on the overall radial shaft-load.
Studies on Performance and Internal Flow of U-Shaped and Snake-Shaped Bend Diffusers: 2nd Report
Authors: Shimizu Yukimaru , Nagafusa Makoto , Sugino Koichi , Kubota Takashi
Published: October 2009

This paper describes the relation between bend diffuser characteristics and internal flow. Diffusers were bent into U and snake shapes within the limitation of a single plane. In these experiments, area ratio, divergent angle and curvature radius ratio of bend elements were varied. Five types of inlet velocity profiles also were used, and their effects on diffuser performance and internal flow were investigated in detail. The following is a report on the fruitful and interesting results we have obtained.
An Application of the Weis-Fogh Mechanism to Ship Propulsion
Authors: Tsutahara M. , Kimura T.
Published: October 2009

A mechanism of hovering flight of small insects which is called the Weis-Fogh mechanism is applied to ship propulsion. A model of the propulsion mechanism is proposed, which is based on a two-dimensional model of the Weis-Fogh mechanism and consists of one or two wings in a square channel. The dynamic properties of the model are studied experimentally, and the propulsive efficiency obtained is as high as 75 percent. A model ship equipped with this propulsion mechanism was made, and working tests performed. The model ship sailed very smoothly and the moving speed of the wings was small compared with the advancing speed of the ship.
Response of an Operational Turbofan Engine to a Simulated Nuclear Blast
Authors: Dunn M. G. , Padova C. , Adams R. M.
Published: October 2009

This paper describes the results of a measurement program designed to determine the transient response of an air-breathing propulsion system to simulated nuclear blast waves. A Ludwieg-tube facility, incorporating a driver technique consisting of an activating chamber and a nonfrangible diaphragm, was used to create the required shock waves. Detailed measurements were performed at incident shock overpressures of approximately 6.9, 10.3, 13.8, and 17.2 kPa (1.0, 1.5, 2.0, and 2.5 psi). For each of these overpressures, data were obtained for engine speeds of 0, 80, 90, and 100 percent of maximum speed. Typical results are presented for distortion patterns at the fan face for both an extended bellmouth and a S-shaped inlet at either 0 or 20 deg yaw angle.
Investigation of Third-Order Closure Model of Turbulence for the Computation of Incompressible Flows in a Channel With a Backward-Facing Step
Authors: Amano R. S. , Goel P.
Published: October 2009

To predict the diffusion process of the Reynolds stresses in reattaching shear flows, the transport model for the triple-velocity products has been developed and tested for the computation of the flow in a channel with a backward-facing step. Upon comparison of the results of uuv, uvv, and vvv with those obtained by using existing algebraic correlations, it was shown that the present model improved the prediction of the triple-velocity products.
Numerical Computation of Phase Separation in Two Fluid Flow
Authors: Carver M. B.
Published: October 2009

A new iterative approach is outlined for multidimensional computational analysis of two fluid flow. Parametric surveys are described to illustrate that the method rationally predicts separation of two fluid flows under gravitational and centrifugal influences. A comparison is made between behavior computed by the method, and results reported in an experimental study of air and water flowing in elbows and pipes.
Hydrodynamics in Tubes Perturbed by Curvilinear Obstructions
Authors: Rastogi A. K.
Published: October 2009

A calculation procedure for two-dimensional separated flows over curved boundaries, e.g., flow in constricted tubes, is described. The method is based on the numerical solution with finite differences of the governing equations in orthogonal curvilinear coordinates. A body fitted curvilinear orthogonal numerical grid is generated first which is then employed for the solution of partial differential equations governing fluid flow. Results of calculations are presented for laminar and turbulent flows in constricted tubes. For turbulent flow calculations the k-ε turbulence model has been employed. Comparison between computed and measured values of flow quantities is also presented and is discussed in some detail. Although the present paper deals only with constricted pipes, the method developed is general and can be used without difficulty for two-dimensional flows over other curved boundaries.
Application of the Adjoint Sensitivity Method to the Analysis of a Supersonic Ejector
Authors: Wacholder E. , Dayan J.
Published: October 2009

Although the concepts of various types of ejectors have been thoroughly discussed in the literature during the past sixty years, a rigorous sensitivity analysis of the ejector’s performance has never been presented. In the present work a sensitivity analysis method, based on the use of adjoint functions, is introduced and applied to the one-dimensional model of a supersonic ejector. The advantage of the proposed method over all other possible techniques is that a single computer run can provide the response function sensitivities with respect to all input parameters. The usefulness of the sensitivity coefficients in predicting the ejector’s performance and the uncertainty involved, as well as in the determination of manufacturing tolerances, is demonstrated and proven to be a powerful tool in the design.
Experimental Study of the Diversion Crossflow Caused by Subchannel Blockages. Part II: Pressures in the Channels and the Comparison of the COBRA III-C Predictions With Experimental Data
Authors: Tapucu A. , Genc¸ay S. , Troche N. , Merilo M.
Published: October 2009

In this research, the hydrodynamic behavior of two laterally interconnected channels with blockages in one of them has been studied experimentally. For blockages of different shapes and severities, the mass flow rates as well as the pressures in the channels upstream and downstream of the blockage were determined. The experiments were conducted on two square channels separated by an intermediate plate with slots of different geometric parameters. Two types of blockages have been considered: plate and smooth. The shape of the smooth blockage was a cosine. The experimental data on the mass flow rates and pressures in the channels have been compared with the predictions of the subchannel code COBRA-III-C. It is observed that COBRA-III-C may not be adequate to describe the hydrodynamic behavior of two-interconnected channels with plate type blockages much higher than 30 percent severity in one of the channels. The limit of applicability of the code in the case of smooth blockages can be safely extended up to 60 percent severity.
One Dimensional Gas Flow With Internal Heating
Authors: Liou C. P. , Wylie E. B.
Published: October 2009

This paper presents a comparison of two solutions, a numerical and an analytic, to an idealized problem of frictionless transient gas flow driven by internal heating. The purpose of such a comparison is to provide a check on a general method for transient gas flow in pipelines with friction and heat transfer. The numerical solution to this problem is formulated based on the method of characteristics with specified time intervals. To avoid interpolation for integration along the characteristics, a multiplier is introduced to the acceleration term in the equation of motion. Favorable comparisons of pressure and density time histories are obtained.
Unified Equation of Motion (UEM) Approach as Applied to S1 Turbomachinery Problems
Authors: Abdallah S. , Smith C. F. , McBride M. W.
Published: October 2009

Incompressible, blade-to-blade (SI surface) flow solutions for stators and rotors of turbomachines are obtained utilizing an approach which combines the equations of motion into a single elliptic, second-order partial differential equation for the streamline field. This Unified Equation of Motion (UEM) is obtained from the momentum equation which is modified by using a stream function that satisfies the continuity equation identically. The unified equation is solved numerically by use of a finite difference technique. The velocity field is determined by differentiation of the stream function field and use of the computed streamlines. The pressure field is then determined from an energy relation along the streamlines. The present method is similar to the classical Streamline Curvature Method (SLCM) in that a computation grid is not required; however, the ellipticity of the flow field is preserved directly by the unified equation of motion. The UEM solution is substantially more stable than the SLC method and yields the periodic stagnation streamlines directly. Body-fitted curvilinear coordinates (quasi-orthogonals and streamlines) are generated naturally by the UEM solution. A number of comparisons of the results of the present method are made with experimental data and results of other numerical methods. These comparisons are made for incompressible two dimensional and quasi-three dimensional stationary and rotating blade sections. There is general agreement with accepted analysis procedures.
Comparison of Minimum Length Nozzles
Authors: Argrow B. M. , Emanuel G.
Published: October 2009

A second-order accurate method-of-characteristics algorithm is used to determine the flow field and wall contour for a supersonic, axisymmetric, minimum length nozzle with a straight sonic line. Results are presented for this nozzle and compared with three other minimum length nozzle configurations. It is shown that the one investigated actually possesses the shortest length as well as the smallest initial wall turn angle at the throat. It also has an inflection point on the wall contour, in contrast to the other configurations.
Adiabatic and Diabatic Flow Studies by Shear Stress Measurements in Annuli With Inner Cylinder Rotation
Authors: Abdallah Y. A. G. , Coney J. E. R.
Published: October 2009

The shear stress, occurring at the outer surface of a vertical annular gap formed by a stationary outer cylinder and a rotatable inner cylinder, was measured for a wide range of conditions, using a flush mounted probe. For annular gaps of radius ratio 0.8 and 0.9, axial flows of Reynolds numbers 100, 165, 200, and 300 were imposed under adiabatic and diabatic upflow and also diabatic downflow conditions. Under these conditions, the shear stress was determined over a range of Taylor numbers approaching 107, the flow being fully developed. Diabatic conditions were achieved by the isothermal heating of the outer surface of the gap. A primary regime, in which Taylor vortices are absent or exist away from the outer surface of the gap was identified. Secondary, tertiary and quaternary regimes, in which the vortex flow is in contact with that surface ensued. The contrast between the results for diabatic upflow and diabatic downflow gives an understanding of the effect of natural convection in these regimes.
Studies of Power Station Feed Pump Loss of Suction Pressure Incidents
Authors: Cranfield R. R.
Published: October 2009

Open cycle feed systems featuring a deaerator followed by the boiler feed pumps have been subject to unexpected loss in net positive suction head during transient operation. This has been traced to separation at the deaerator storage tank drain and the formation of a steam/water interface in the downcomer to the pumps. The outflow at separation when the storage tank water is subcooled is generally much greater than the maximum suction flow corresponding to the unit rating, but when the tank water boils, as during transients, it may be very much less. Thus with a high suction flow in the boiling mode, the new interface may descend in the downcomer to result in feed pump cavitation, pressure imbalance, vapor locking, severe vibration, damage to the pump and an inability to maintain forward flow. Model tests have been conducted to establish the criterion for the separation in terms of the critical outflow for specific operating conditions as a function of geometric ratios involving tank-water depth and tank/downcomer dimensions. The data obtained although scattered are in general agreement with the data from actual plant and may be used to assess safe operating parameters.
Kilovoltage beam Monte Carlo dose calculations in submillimeter voxels for small animal radiotherapy
Authors: Bazalova Magdalena , Zhou Hu , Keall Paul J. , Graves Edward E.
Published: October 2009

Purpose:

Small animal conformal radiotherapy (RT) is essential for preclinical cancer research studies and therefore various microRT systems have been recently designed. The aim of this paper is to efficiently calculate the dose delivered using our microRT system based on a microCT scanner with the Monte Carlo (MC) method and to compare the MC calculations to film measurements.

Methods:

Doses from diameter photon beams deposited in a solid water phantom with voxels are calculated using the latest versions of the EGSnrc codes BEAMNRC and DOSXYZNRC. Two dose calculation approaches are studied: a two‐step approach using phase‐space files and direct dose calculation with BEAMNRC simulation sources. Due to the small beam size and submillimeter voxel size resulting in long calculation times, variance reduction techniques are studied. The optimum bremsstrahlung splitting number (NBRSPL in BEAMNRC) and the optimum DOSXYZNRC photon splitting number are examined for both calculation approaches and various beam sizes. The dose calculation efficiencies and the required number of histories to achieve 1% statistical uncertainty—with no particle recycling—are evaluated for beams. As a final step, film dose measurements are compared to MC calculated dose distributions.

Results:

The optimum NBRSPL is approximately for both dose calculation approaches. For the dose calculations with phase‐space files, varies only slightly for beams and is established to be 300. for the DOSXYZNRC calculation with the BEAMNRC source ranges from 300 for the beam to 4000 for the beam. The calculation time significantly increases for small beam sizes when the BEAMNRC simulation source is used compared to the simulations with phase‐space files. For the 2 and beams, the dose calculations with phase‐space files are more efficient than the dose calculations with BEAMNRC sources by factors of 54 and 1.6, respectively. The dose calculation efficiencies converge for beams with diameters larger than .

Conclusions:

A very good agreement of MC calculated dose distributions to film measurements is found. The mean difference of percentage depth dose curves between calculated and measured data for 2, 5, 10, and beams is 1.8%.
A robotic system for ‐FMISO PET‐guided intratumoral measurements
Authors: Chang Jenghwa , Wen Bixiu , Kazanzides Peter , Zanzonico Pat , Finn Ronald D. , Fichtinger Gabor , Ling C. Clifton
Published: October 2009

An image‐guided robotic system was used to measure the oxygen tension in rodent tumor xenografts using interstitial probes guided by tumor hypoxia PET images. Rats with diameter tumors were anesthetized and immobilized in a custom‐fabricated whole‐body mold. Imaging was performed using a dedicated small‐animal PET scanner (R4 or Focus 120 microPET™) after the injection of the hypoxia tracer ‐fluoromisonidazole (‐FMISO). The coordinate systems of the robot and PET were registered based on fiducial markers in the rodent bed visible on the PET images. Guided by the 3D microPET image set, measurements were performed at various locations in the tumor and compared to the corresponding ‐FMISO image intensity at the respective measurement points. Experiments were performed on four tumor‐bearing rats with 4 (86), 3 (80), 7 (162), and 8 (235) measurement tracks (points) for each experiment. The ‐FMISO image intensities were inversely correlated with the measured , with a Pearson coefficient ranging from to for the 22 measurement tracks. The cumulative scatterplots of versus image intensity yielded a hyperbolic relationship, with correlation coefficients of 0.52, 0.48, 0.64, and 0.73, respectively, for the four tumors. In conclusion, PET image‐guided measurement is feasible with this robot system and, more generally, this system will permit point‐by‐point comparison of physiological probe measurements and image voxel values as a means of validating molecularly targeted radiotracers. Although the overall data fitting suggested that ‐FMISO may be an effective hypoxia marker, the use of static ‐FMISO PET postinjection scans to guide radiotherapy might be problematic due to the observed high variation in some individual data pairs from the fitted curve, indicating potential temporal fluctuation of oxygen tension in individual voxels or possible suboptimal imaging time postadministration of hypoxia‐related trapping of ‐FMISO.
MRI of prostate brachytherapy seeds at high field: A study in phantom
Authors: Thomas S. D. , Wachowicz K. , Fallone B. G.
Published: October 2009

Postimplant evaluation of prostate brachytherapy using magnetic resonance imaging (MRI) at 1.5 T has met with some difficulties due to the uncertainty associated with seed localization despite the excellent anatomical delineation this imaging modality can achieve. Seeds in vascularized regions or outside the prostate, where signal heterogeneity or drop off can obscure their position, can be difficult to identify. The increase in SNR available at 3.0 T offers the potential to improve these issues with visualization. However, before moving directly to in vivo studies, it is important to investigate the effects of artifact size on the ability to localize multiple seeds in close proximity. These artifacts are of extra concern at higher field because of the increased induced field distortions surrounding the seeds. A single prostate brachytherapy seed (IMC6711, OncoSeed™) and arrays of seed pairs were suspended in a porcine gel medium and imaged on 1.5 and 3 T MRI scanners for comparison. Two basic acquisition techniques utilized in a wide array of clinical sequences [spin‐echo based and gradient‐echo (GE) based] were investigated for the types of artifacts they produce, and their dependence on field. Analysis of the resulting voids was performed to determine the relative size of seeds as seen on the images, as well as the ability to distinguish seeds at close proximity. The seed voids at 3 T were only slightly larger than those obtained at 1.5 T (0.5 mm longer and wider) when using a spin‐echo type sequence. For this work, the authors used a proton density fast spin‐echo (FSE) sequence. These results are promising for the use of 3 T imaging for postimplant evaluation since the SNR will increase by roughly a factor of 2 with only a limited corresponding increase in artifact size. The minimum separation of the seeds to be completely distinguished using void analysis increased from between 1.5 and 3 mm to between 3 and 4.5 mm when going from 1.5 to 3 T FSE imaging. The minimum separation of the seeds for GE at the demonstration TE of 11 ms was found to be between 3 and 4.5 mm for 1.5 T and between 4.5 and 6 mm for 3 T. These GE artifact dimensions will scale down with TE and, as this happens, approach the dimensions of the FSE artifacts given above.
Fast Monte Carlo simulation on a voxelized human phantom deformed to a patient
Authors: Bueno G. , Déniz O. , Carrascosa C. B. , Delgado J. M. , Brualla L.
Published: October 2009

Purpose:

A method for performing fast simulations of absorbed dose using a patient's computerized tomography (CT) scan without explicitly relying on a calibration curve is presented.

Methods:

The method is based on geometrical deformations performed on a standard voxelized human phantom. This involves spatially transforming the human phantom to align it with the patient CT image. Since the chemical composition and density of each voxel are given in the phantom data, a calibration curve is not used in the proposed method. For this study, the Monte Carlo (MC) code PENELOPE has been used as the simulation of reference. The results obtained with PENELOPE simulations are compared to those obtained with PENFAST and with the collapsed cone convolution algorithm implemented in a commercial treatment planning system.

Results:

The comparisons of the absorbed doses calculated with the different algorithms on two patient CTs and the corresponding deformed phantoms show a maximum distance to agreement of, and in general, the obtained absorbed dose distributions are compatible within the reached statistical uncertainty. The validity of the deformation method for a broad range of patients is shown using MC simulations in random density phantoms. A PENFAST simulation of a photon beam impinging on a patient CT reaches 2% statistical uncertainty in the absorbed dose, in a voxel along the central axis, in running on a single core of a CPU.

Conclusions:

The proposed method of the absorbed dose calculation in a deformed voxelized phantom allows for dosimetric studies in the geometry of a patient CT scan. This is due to the fact that the chemical composition and material density of the phantom are known. Furthermore, simulation using the phantom geometry can provide dosimetric information for each organ. The method can be used for quality assurance procedures. In relation to PENFAST, it is shown that a purely condensed‐history algorithm (class I) can be used for absorbed dose estimation in patient CTs.
THE EFFECTS OF TAXI ON TRAFFIC FLOW
Authors: TANG TIE-QIAO , LI YAN , HUANG HAI-JUN
Published: October 2009

Taxi will come to one complete halt during the boarding/alighting period and might produce stop-and-go without passengers, so it often produces traffic interruption on the single-lane system. Tang et al. pointed out that the traffic flow model [Chin. Phys.18, 975 (2009)] can be used to directly describe various micro phenomena resulted by traffic interruption on the single-lane system, if we properly define the traffic interruption probability, so in this paper we adopt this model to study the micro phenomena resulted by taxi on the single-lane system. The numerical results show that this model can describe the effects that taxi has on the trails of each vehicle's motion and the evolutions of the flow and the density on the single-lane system, but that these effects are relevant to the initial conditions of the whole system.
INFORMATION-BASED EVACUATION EXPERIMENT AND ITS CELLULAR AUTOMATON SIMULATION
Authors: YANG LIZHONG , LIU SHAOBO , LI JIAN , ZHU KONGJIN , FANG TINGYONG
Published: October 2009

The evacuation process under emergency is studied by means of experiments and simulations, focusing on the influence of the environment information. A revised cellular automaton model in which environment information is considered as "static information" (building structure, spatial distance, etc.) and "dynamic information" (sounds of fire alarm, etc.) is introduced. Two scenarios, including evacuation with and without visibility in a classroom, are studied to investigate the different influence of the two kinds of information on human behavior. The experimental and simulation results demonstrate that:

(1) to intensify the spatial distance information can reduce the evacuation time;

(2) the spatial distance is not the only decisive factor especially in evacuation without visibility because the sound information, which is ignorable in evacuation with visibility, is playing a more important role under this condition;

(3) the intensity of static information can reflect evacuees' familiarity of the environment;

(4) the model can reproduce the experiments well, and the simulation method is useful for further study of the crowd movement simulation.
VISCOELASTIC PROPERTIES OF NETWORKS
Authors: GÜNDÜZ GÜNGÖR
Published: October 2009

A network was characterized by its viscoelastic properties. The viscoelastic property indicates the deformations or changes in the shape and in the internal structure during the evolution of a network. The change in the direction of motion was taken as elastic deformation and the change in the vertical direction as viscous deformation. These deformations were related to the change of geometry of internal structure and of shape. Thus it was possible to characterize a network by its storage and loss moduli. The change of the structure of a network during its evolution changes also its entropy. However entropy depends on the number of microstates of an already existing framework. As examples, two different systems (i) New York Stock Exchange and (ii) a melody were studied for their viscoelastic properties. The change of viscous property was compared with the change of different types of entropies such as configurational entropy, crossing entropy, and topological entropy. This last entropy was introduced and explained in the text. It was found out that there is no direct correspondence between the increase of entropy and the increase of viscous property of a network although they sometimes correlate with each other.
TAMING CHAOTIC ARRAYS BY PARAMETRIC EXCITATION WITH PROPER RANDOM PHASE
Authors: YUNG KAI LEUNG , LEI YOUMING , XU YAN
Published: October 2009

A weak harmonic parametric excitation with random phase has been introduced to tame chaotic arrays. It has been shown that when the amplitude of random phase properly increases, two different kinds of chaotic arrays, unsynchronized and synchronized, can be controlled by the criterion of top Lyapunov exponent. The Lyapunov exponent was computed based on Khasminskii's formulation and the extension of Wedig's algorithm for linear stochastic systems. In particular, it was found that with stronger coupling the synchronized chaotic arrays are more controllable than the unsynchronized ones. The bifurcation analysis, the spatiotemporal evolution, and the Poincaré map were carried out to confirm the results of the top Lyapunov exponent on the dynamical behavior of control stability. Excellent agreement was found between these results.
NUMERICAL STUDY OF ASYMMETRIC EFFECT ON A PITCHING FOIL
Authors: XIAO QING , LIAO WEI
Published: October 2009

This study investigates numerically the effect of asymmetric sinusoidal oscillating motion on the propulsion performance of a pitching foil and attempts to gain insight in whether the low thrust generated by pure pitching could be improved by asymmetric motion. The propulsion performance and flow structure are explored by solving the unsteady Navier–Stokes equations. Computations are conducted for a range of oscillation frequency, pitching amplitude, and asymmetry. The results show that the higher asymmetry can induce the stronger reverse Von Karman vortex in the wake, which in turn leads to the increased thrust. However, the propulsion efficiency reduces as increasing asymmetry. Computed results are further adopted to shed insight into the mechanism of thrust enhancement.
A Study on the Antioxidant Activity and Tissues Selective Inhibition of Lipid Peroxidation by Saponins from the Roots of Platycodon grandiflorum
Authors: Fu Xian-Jun , Liu Hong-Bing , Wang Peng , Guan Hua-Shi
Published: October 2009

Platycodi Radix is the root of Platycodon grandiflorum (Jacq.) A. DC and has been used as a traditional medicine in China. According to the theory of traditional Chinese medicine, Platycodi Radix (PR) possesses the character of lung meridian tropism (Guijing) and has selective effects on the lung and respiratory system. The aim of this study was to confirm the antioxidant effects of saponins from Platycodi Radix (PRS), with emphasis on its selective inhibition of lipid peroxidation in different tissues. The hydroxyl radical scavenging activity was determined by a H2O2/Fe2+ system; a modified thiobarbituric acid reactive species assay was used to measure the lipid peroxide in rats' tissues. These antioxidant activities were compared to ascorbic acid (Vc). The results showed that PRS had antioxidant activities in various antioxidant systems. And the inhibition capability of lipid peroxidation of PRS and Vc were excellent, but differed greatly in different tissues. These results suggested that PRS had antioxidant effects and selective inhibition of lipid peroxidation. It indicated that the mechanism of Platycodi Radix to treat some diseases might be related to its antioxidant activity, especially its tissue selective effects. However, further study is needed.
EXACT SOLUTIONS AND THEIR DYNAMICS OF TRAVELING WAVES IN THREE TYPICAL NONLINEAR WAVE EQUATIONS
Authors: LI JIBIN , ZHANG YI , CHEN GUANRONG
Published: October 2009

It was reported in the literature that some nonlinear wave equations have the so-called loop- and inverted-loop-soliton solutions, as well as the so-called loop-periodic solutions. Are these true mathematical solutions or just numerical artifacts? To answer the question, this article investigates all traveling wave solutions in the parameter space for three typical nonlinear wave equations from a theoretical viewpoint of dynamical systems. Dynamical analysis shows that all these loop- and inverted-loop-solutions are merely visual illusion of numerical artifacts. To reveal the nature of such special phenomena, this article also offers the mathematical parametric representations of these traveling wave solutions precisely in analytic forms.
NONLINEAR STATISTICS OF HUMAN SPEECH DATA
Authors: BROWN KENNETH A. , KNUDSON KEVIN P.
Published: October 2009

We study the structure of point clouds obtained as time delay embeddings of human speech signals by approximating the data sets with certain simplicial complexes and analyzing their persistent homology. Results for several different sounds are presented in embedding dimensions 3 and 4. The first Betti number allows a coarse classification of sounds into three groups: vowels, nasals and noise.
BOHMIAN TRAJECTORIES AND THE PATH INTEGRAL PARADIGM: COMPLEXIFIED LAGRANGIAN MECHANICS
Authors: SBITNEV VALERIY I.
Published: October 2009

David Bohm had shown that the Schrödinger equation, that is a "visiting card" of quantum mechanics, can be decomposed onto two equations for real functions — action and probability density. The first equation is the Hamilton–Jacobi (HJ) equation, a "visiting card" of classical mechanics, is modified by the Bohmian quantum potential. This potential is a nonlinear function of the probability density. And the second is the continuity equation. The latter can be transformed to the entropy balance equation. The Bohmian quantum potential is transformed into two Bohmian quantum correctors. The first corrector modifies the kinetic energy term of the HJ equation, and the second one modifies the potential energy term. The unification of the quantum HJ equation and the entropy balance equation gives a complexified HJ equation containing complex kinetic and potential terms. The imaginary parts of these terms have an order of smallness about the Planck constant. The Bohmian quantum corrector is an indispensable term modifying the Feynman's path integral by expanding coordinates and momenta to an imaginary sector. The difference between the Bohmian and Feynman's trajectories is that the former satisfies the principle of least action and they bifurcate on interfaces. The latter covers all possible paths from a source to a detector. They can split and annihilate.
ENRICHED DYNAMICS OF A SIMPLE NONLINEAR NONAUTONOMOUS PARALLEL LCR CIRCUIT
Authors: MANIMEHAN I. , THAMILMARAN K. , PHILOMINATHAN P.
Published: October 2009

We present the results of a very simple nonlinear nonautonomous parallel LCR circuit which exhibits a rich variety of bifurcations and chaos. This simple experimental chaotic oscillator is made up of a few passive components and a uniquely designed nonlinear element comprising of a junction diode and Op-amp based negative conductor. The system exhibits a rich dynamics such as chaos via torus breakdown, period-doubling, period three-doubling, period-adding, Farey sequences, etc., and the results of the investigation are vividly presented along with experimental, numerical and analytical evidences. The laboratory experimental outcomes are in agreement with the numerical and analytical results.
CHAOS CONTROL IMPLEMENTATION BY INTERRUPTED ELECTRIC CIRCUIT WITH SWITCHING DELAY
Authors: KOUSAKA TAKUJI , UETA TETSUSHI , MA YUE
Published: October 2009

We have demonstrated that the chaotic circuit with a switching delay is modeled by a return map, and a controller for the suppression of chaos is proposed. A circuit representing a controller stabilizing a period-1 unstable periodic orbit in an interrupted electric circuit with a certain switching delay is also discussed.
ON PLANAR PIECEWISE AND TWO-TORUS PARABOLIC MAPS
Authors: ASHWIN PETER , FU XINCHU , LIN CONGPING
Published: October 2009

We investigate properties and examples of iterated planar piecewise parabolic (PWP) maps, including those induced by two-torus parabolic maps and their inverses. PWP maps are area-preserving maps that have constant linearizations but only one eigenvector with eigenvalue one. We obtain necessary and sufficient conditions for a two-torus parabolic map to be invertible.

For noninvertible PWP maps, there are a number of questions about the existence and structure of attractors for such maps. We introduce the simplest example of a nontrivial PWP map, defined by a parabolic linear map with a translation that is a different constant on each side of a given line in the plane. For this "half plane parabolic map" we obtain sufficient conditions for a bounded attractor to exist, discuss their dynamical properties and give some examples of these and related maps.
MODELING OF NON-HBL VHE γ-RAY BLAZARS
Authors: BÖTTCHER MARKUS
Published: October 2009

This is a summary of recent modeling results of three newly detected TeV blazars of the intermediate BL Lac object (IBL) and flat-spectrum radio quasar (FSRQ) sub-classes: W Comae, 3C 66A, and 3C 279. For model fits to the spectral energy distributions of W Comae and 3C 66A, a non-negligible contribution from a source of soft radiation external to the jets of these blazars is strongly preferred over pure synchrotron-self-Compton or synchrotron-proton-blazar models, respectively. This indicates that IBLs are truly intermediate between the "classical" TeV blazars (high-frequency-peaked BL Lac objects) and FSRQs. The VHE γ-ray detection of the FSRQ 3C 279 poses severe challenges for leptonic models, and seems to favor a hadronic origin of the high-energy emission. However, even a hadronic model suffers from problems with extreme energy requirements.
A SHORT, CRITICAL REVIEW ON GAMMA-RAY EMISSION FROM GALAXY CLUSTERS
Authors: COLAFRANCESCO SERGIO
Published: October 2009

We discuss the relevance of gamma-ray observations of galaxy clusters, to unveil several issues that are relevant for Cosmology and Astro-Particle Physics of cosmic structures: the nature of Dark Matter, the origin of cosmic rays and the impact of black holes.