bluuebunny/crossref_metadata_2025 huggingface dataset:
Clinical Implementation of Dual‐Source Computed Tomography for Diagnostic Cardiovascular Angiography: Initial Experience
Authors: Dikkers R. , De Jonge G. J. , Willems T. P. , Van Ooijen P. M. A. , Piers L. H. , Tio R. A. , Oudkerk M.
Published: September 2006

Coronary angiography (CAG) has been the standard method for detection and follow‐up of coronary artery disease for years. However, it has a slight but discrete complication rate. With the introduction of multidetector computed tomography (MDCT), the coronary system could be evaluated non‐invasively. The limited temporal and spatial resolution of the first MDCT scanners made the examination quality of scanning of patients with high, increasing or irregular heart rates or patients with stents, clips or severely calcified arteries less predictable. The introduction of dual‐source computed tomography (DSCT) might constitute a promising new concept for cardiac CT. In this study, we present our first experience with DSCT. We investigated seven patients for different indications with DSCT. Image quality was reliable in all patients despite the presence of high heart rates (up to 105 beats per minute), heavy calcifications and surgical clips. DSCT showed stenoses which were not detected on CAG. Regarding the fact that DSCT not only offers morphological information of the coronary vessel wall and lumen but also delivers all standard functional cardiac parameters, it has true potential as a routine diagnostic tool in the cardiac diagnostic workup. In conclusion, first results of DSCT show high‐quality, consistent cardiac and coronary imaging independent of heart rate and patient condition. These features enable a breakthrough in non‐invasive cardiac and coronary imaging.
Genetic Variation in Fragmented Forest Stands of the Andean Oak Quercus humboldtii Bonpl. (Fagaceae)1
Authors: Fernández‐M. Juan F. , Sork Victoria L.
Published: September 2006

Quercus humboldtii is a montane forest dominant species in Colombia, which has experienced significant habitat loss. Using three microsatellite loci, we compared the genetic diversity of adults and seedlings in fragments of small and large size. Results show high genetic diversity, comparable to other temperate oak species (Ho= 0.813, He= 0.780, and f=−0.044). However, allelic richness reduction in seedlings of the most fragmented part of the landscape, suggested restricted gene flow and risk of future genetic bottlenecks, if larger tracts of forest disappear.
MENTAL HEALTH AND JUVENILE ARRESTS: CRIMINALITY, CRIMINALIZATION, OR COMPASSION?*
Authors: HIRSCHFIELD PAUL , MASCHI TINA , WHITE HELENE RASKIN , TRAUB LEAH GOLDMAN , LOEBER ROLF
Published: September 2006

Juveniles in secure confinement allegedly suffer from more mental health problems than their peers. This may reflect background and behavioral characteristics commonly found in clients of both mental health and juvenile justice systems. Another explanation is that mental disorders increase the risk of arrest. These interpretations were tested on a sample of Pittsburgh boys (n = 736). Findings indicate that arrested youth exhibit more attention deficit hyperactivity (ADH) problems, oppositional defiant (OD) problems, and nondelinquent externalizing symptoms prior to their first arrests compared to their never‐arrested peers. However, arrested and nonarrested youth score similarly on prior affective and anxiety problems and internalizing symptoms. Net of delinquency, substance use, and other selection factors, internalizing problems lower the risk of subsequent arrest, whereas OD problems and nondelinquent externalizing symptoms increase it. ADH problems have no effect on arrest net of delinquency and substance use. These findings lend only partial support to the criminalization hypothesis. Whereas some mental health symptoms increase the risk of arrest, others elicit more cautious or compassionate official responses.
VARIATION IN TRIAL PENALTIES AMONG SERIOUS VIOLENT OFFENSES*
Authors: ULMER JEFFERY T. , BRADLEY MINDY S.
Published: September 2006

We examine the differences in the sentencing of those who plead guilty and those convicted by jury trial among defendants convicted of serious violent offenses. Drawing from a focal concerns and court communities perspective on court decision making, we develop several hypotheses about jury trial penalties for serious violent offenders, and how such penalties may vary by offense characteristics, defendant characteristics, and court contexts. Our hierarchical models using Pennsylvania sentencing data from 1997 to 2000 reveal that defendants are substantially penalized if they exercise their right to a jury trial and then lose. Furthermore, this jury trial penalty is not evenly assessed, but depends on the seriousness and type of offense, defendant criminal history, and court contextual characteristics such as caseload, court community size, local violent crime rates, and the size of local black populations.
CORPORATE SELF‐POLICING AND THE ENVIRONMENT*
Authors: STRETESKY PAUL B.
Published: September 2006

The U.S. Environmental Protection Agency's Self‐Policing Policy (more commonly referred to as the Audit Policy) waives or reduces penalties when regulated entities voluntarily discover, disclose, and correct environmental violations. This study draws upon a rational choice model of corporate crime to determine if traditional regulatory efforts such as inspections and enforcement actions are associated with the odds of disclosing an environmental violation under the Audit Policy. A case control design is used to compare companies that self‐police to companies that do not self‐police. The event group consists of all 551 companies that disclosed at least one environmental violation under the Audit Policy between October 1, 1998 and September 30, 2000. The control group consists of a simple random sample of 551 companies that did not use the Audit Policy but were discovered to have violated at least one environmental law during the same time period as the event group. There is no evidence that inspections and enforcement increase Audit Policy use. However, the results do suggest, first, that the Audit Policy is more likely to be used by large companies than by small companies and, second, that it is likely to be used for reporting violations as opposed to more serious emissions or permit violations. In terms of public policy these findings suggest that regulatory agencies such as the EPA can do relatively little to increase the self‐policing of environmental violations.
DRIVING WHILE BLACK: BIAS PROCESSES AND RACIAL DISPARITY IN POLICE STOPS*
Authors: WARREN PATRICIA , TOMASKOVIC‐DEVEY DONALD , SMITH WILLIAM , ZINGRAFF MATTHEW , MASON MARCINDA
Published: September 2006

We estimate the degree of racial disparity in police vehicular stops separately for local and state police in North Carolina in the year 2000. We introduce four mechanisms that might produce racial disparities in police stops—racial profiling, race sensitive police deployment, cognitive bias and stereotyping, and prejudice. We then model the relative odds of police vehicle stops as a function of race, driving behavior, and other demographic statuses separately by police organization type, with controls for omitted variable bias at both the driver and spatial level. We find only weak evidence of racial disparity in stops by officers of the state highway patrol but stronger evidence in those made by local police officers.
DOES CORRECTIONAL PROGRAM QUALITY REALLY MATTER? THE IMPACT OF ADHERING TO THE PRINCIPLES OF EFFECTIVE INTERVENTION*
Authors: LOWENKAMP CHRISTOPHER T. , LATESSA EDWARD J. , SMITH PAULA
Published: September 2006

Research Summary:

This study analyzed data on 3,237 offenders placed in 1 of 38 community‐based residential programs as part of their parole or other post‐release control. Offenders terminated from these programs were matched to, and compared with, a group of offenders (N = 3,237) under parole or other post‐release control who were not placed in residential programming. Data on program characteristics and treatment integrity were obtained through staff surveys and interviews with program directors. This information on program characteristics was then related to the treatment effects associated with each program.

Policy Implications:

Significant and substantial relationships between program characteristics and program effectiveness were noted. This research provides information that is relevant to the development of correctional programs, and it can be used by funding agencies when awarding contracts for services.
SCARLET LETTERS AND RECIDIVISM: DOES AN OLD CRIMINAL RECORD PREDICT FUTURE OFFENDING?*
Authors: KURLYCHEK MEGAN C. , BRAME ROBERT , BUSHWAY SHAWN D.
Published: September 2006

Research Summary:

This research explores the issue of old prior records and their ability to predict future offending. In particular, we are interested in the question of whether, after a given period of time, the risk of recidivism for a person who has been arrested in the distant past is ever indistinguishable from that of a population of persons with no prior arrests. Two well‐documented empirical facts guide our investigation: (1) Individuals who have offended in the past are relatively more likely to offend in the future, and (2) the risk of recidivism declines as the time since the last criminal act increases. We find that immediately after an arrest, the knowledge of this prior record does significantly differentiate this population from a population of nonoffenders. However, these differences weaken dramatically and quickly over time so that the risk of new offenses among those who last offended six or seven years ago begins to approximate (but not match) the risk of new offenses among persons with no criminal record.

Policy Implications:

Individuals with official records of past offending behavior encounter a barrier when they try to obtain employment, even if a person's most recent offense occurred in the distant past. There are many reasons for such obstacles, but they are at least partially premised on the concern that individuals with arrest records—even from the distant past—are more likely to offend in the future than persons with no criminal history. Our analysis questions the logic of such practices and suggests that after a given period of remaining crime free, it may be prudent to wash away the brand of “offender” and open up more legitimate opportunities to this population.
PROPOSITION 8 AND CRIME RATES IN CALIFORNIA: THE CASE OF THE DISAPPEARING DETERRENT
Authors: WEBSTER CHERYL MARIE , DOOB ANTHONY N. , ZIMRING FRANKLIN E.
Published: September 2006

Research Summary:

In 1999, Daniel Kessler and Steven Levitt published an article that purported to provide support for the marginal deterrent effects of harsher sanctions on levels of crime. Specifically, they concluded that sentence enhancements that came into effect in California in June 1982 as a result of Proposition 8 were responsible for a subsequent drop in serious crime in this state. Our article examines the analyses and findings of this article and suggests that their conclusion of a deterrent impact fails to withstand scrutiny when more complete and more detailed crime data are used and the comparability of “control” groups is carefully examined. In particular, the addition of annual crime levels for all years (versus only the odd‐numbered years that Kessler and Levitt examine) calls into question the prima facie support for a deterrent effect presented by Kessler and Levitt. Specifically, it demonstrates not only that the crime drop in California began before, rather than after, the passing into law of the sentence enhancements in 1982 but also that the downward slope did not accelerate after the change in law. Furthermore, the comparability of the two “control” groups with the “treatment” group is challenged, rendering suspect any findings based on these comparisons.

Policy Implications:

Case studies suggesting that crime decreased after the imposition of harsh sentencing policies are often cited as evidence of marginal general deterrence. As has been demonstrated in other contexts, the question that needs to be asked is “Compared with what?” Kessler and Levitt's (1999) article demonstrates that those interested in sentencing policy need to be sensitive not only to the appropriateness of the comparisons that are made, but also to the choice of data that are presented.
Should a Cosmopolitan Worry about the “Brain Drain”?
Authors: Kapur Devesh , McHale John
Published: September 2006

Many developing countries are experiencing high rates of emigration of their highly skilled citizens. This essay asks if a cosmopolitan—who we take to be generally supportive of freer international migration—should worry about the adverse effects on those remaining behind in poor countries. We document the extent of skilled outflows, discuss the causes and consequences of those outflows, and offer principles to guide a cosmopolitan policy response. We argue that skilled emigration harms long-run institutional development. The right response, however, is not to shut down the one reasonably liberal element of the international migration regime but to look for ways to make international migration work better for development.
Holes in the Rights Framework: Racial Discrimination, Citizenship, and the Rights of Noncitizens
Authors: Goldston James A.
Published: September 2006

In recent years, states have increasingly exploited their traditional discretion over matters of citizenship to carve out significant exceptions to the universality of human rights protection. This primarily occurs in two ways: through denial and deprivation of citizenship and through the imposition of illegitimate distinctions between citizens and noncitizens. The results of such actions may be physical expulsion, disenfranchisement, exclusion from access to public benefits, and acts of violence and discrimination. The potential for abuse is heightened for racial and ethnic minorities. Racial discrimination is a major cause of denationalization and restrictive access to citizenship. And citizenship status is often used as a proxy for racial grounds in justifying denial of other human rights. The treatment of noncitizens compellingly tests societies' commitments to the rule of law. This essay explores how human rights norms—particularly the body of law that forbids discrimination on grounds of racial or ethnic origin—can be deployed to combat the worst effects of citizenship denial and ill-treatment of non-citizens. It recommends that the problem be addressed through three principal activities: documentation and public education; clarification and distillation of legal standards related to citizenship; and enforcement of existing norms, including those prohibiting racial discrimination.
Sensor Placement for Angular Velocity Determination
Authors: Genin Guy M. , Genin Joseph
Published: September 2006

Velocity transducer placement to uniquely determine the angular velocity of a rigid body is investigated. The angular velocity of a rigid body can be determined with no fewer than five properly placed velocity transducers, if no other types of sensors are present and no algebraic constraint equation involving the angular velocity vector can be written. Complete characterization of the velocity of a rigid body requires six transducers. Choice of transducer placement and orientation requires care, as suboptimal transducer placement can result in data from which the determination of a unique angular velocity vector is impossible. Conditions for successful transducer placement are established, and two examples of adequate transducer placement are presented: an Earth-penetrating projectile, and a bioengineering device for the measurement of head motion.
Transient Fueling Controller Identification for Spark Ignition Engines
Authors: Franchek Matthew A. , Mohrfeld Jackie , Osburn Andy
Published: September 2006

Presented in this paper is a feedforward fueling controller identification methodology for the transient fueling control of spark ignition (SI) engines. The hypothesis of this work is that the feedforward fueling control of SI engines can be separated into steady state and transient phenomena and that the majority of the nonlinear behavior associated with engine fueling can be captured with nonlinear steady state models. The proposed transient controller identification process is built from standard nonparametric identification techniques followed by parametric model recovery. Crank angle serves as the independent variable for these models. Two separate system identification problems are solved to identify the air path dynamics and the fueling path dynamics. The transient feedforward controller is then calculated as the ratio of the air path-over-the fueling path dynamics thereby coordinating the engine fueling with the air path dynamics. It will be shown that a linear transient feedforward-fueling controller operating in tandem with a nonlinear steady state fueling controller can achieve air-fuel ratio regulation comparable to the production fueling controller without the extensive controller calibration process. The engine used in this investigation is a 1999 Ford 4.6L V-8 fuel injected engine.
Estimating Model Uncertainty using Confidence Interval Networks: Applications to Robust Control
Authors: Buckner Gregory D. , Choi Heeju , Gibson Nathan S.
Published: September 2006

Robust control techniques require a dynamic model of the plant and bounds on model uncertainty to formulate control laws with guaranteed stability. Although techniques for modeling dynamic systems and estimating model parameters are well established, very few procedures exist for estimating uncertainty bounds. In the case of H∞ control synthesis, a conservative weighting function for model uncertainty is usually chosen to ensure closed-loop stability over the entire operating space. The primary drawback of this conservative, “hard computing” approach is reduced performance. This paper demonstrates a novel “soft computing” approach to estimate bounds of model uncertainty resulting from parameter variations, unmodeled dynamics, and nondeterministic processes in dynamic plants. This approach uses confidence interval networks (CINs), radial basis function networks trained using asymmetric bilinear error cost functions, to estimate confidence intervals associated with nominal models for robust control synthesis. This research couples the “hard computing” features of H∞ control with the “soft computing” characteristics of intelligent system identification, and realizes the combined advantages of both. Simulations and experimental demonstrations conducted on an active magnetic bearing test rig confirm these capabilities.
Distributed Robust Control of Compliant Framed Wheeled Modular Mobile Robots
Authors: Zhu Xiaorui , Minor Mark A. , Park Sungyong
Published: September 2006

A distributed robust controller for Compliant Framed wheeled Modular Mobile Robots (CFMMR) is studied in this paper. This type of wheeled mobile robot uses rigid axles coupled by compliant frame modules to provide both full suspension and enhanced steering capability without additional hardware. In this research, a distributed nonlinear damping controller using backstepping techniques for wheel-torque control is first developed for single-axle unicycle type robots. The controller is then extended to multiple-axle CFMMR configurations and is robust to disturbances created by modeling errors; especially highly nonlinear frame forces caused by axle interaction. In particular, the controller considers time-varying reference velocities and allows the robot to perform posture regulation, path following, or general trajectory tracking. A two-axle scout CFMMR configuration is used to evaluate the controller. Simulation and experimental results verify robust dynamic motion control of path following.
Heterodyne Digital Control of a High-Frequency Micromechanical Oscillator
Authors: Kriewall Thomas E. , Garbini Joseph L. , Sidles John A. , Jacky Jonathan P.
Published: September 2006

In this paper we present heterodyne control as a technique for digital feedback control of a high-frequency, narrowband micromechanical oscillator. In this technique, isolated and synchronized hardware downconversion and upconversion components are used in conjunction with digital signal processing (DSP) to control the oscillator. Heterodyne control offers reduced computational effort for the digital control of high-frequency, narrow band system, the reduction of noise outside the pass-band, and the generation of lock-in amplifier signals. We present heterodyne control with design criteria in the context of magnetic resonance force microscopy (MRFM) cantilever control. Finally, we present experimental results of heterodyne control applied to an emulated radio-frequency microcantilever system.
Identification of the Heat Flux in a Quasi-Static Thermoelastic System
Authors: Kolmanovsky Ilya , Polis Michael P. , Sivergina Irina F.
Published: September 2006

This paper treats the problem of estimating the heat flux through the free end of a thermoelastic rod, which is allowed to come into contact with a rigid obstacle. This problem is motivated by the need to develop techniques for indirect measurement of heating in applications, such as, brake systems and machine tools. Under a quasi-static approximation, the problem becomes that of characterizing thermal processes in the rod. Assuming that direct and exact measurements at the contacting end of the rod cannot be taken, the problem is to determine if there is contact with the obstacle; and if there is contact, to characterize the conductivity processes at the contacting end. We study the case of weighted-average temperature measurements throughout the rod. Identifiability results and on-line recursive estimation procedures are developed.
LMI Based to Robust Genetic Control Design for a Class of Uncertain Neutral Systems With State and Input Delays
Authors: Chen Jenq-Der
Published: September 2006

In this paper, a robust genetic control design problem for a class of uncertain neutral delay systems in state and control input is considered. The methodology is based on the constructive use of the Lyapunov functional, and a new delay-dependent stabilization criterion is proposed to guarantee robust stability for the systems via linear control. Linear matrix inequality (LMI) and genetic algorithm (GA) are used to seek the state-feedback gain without complex mathematics.
Design of Feedback Systems With Plant Input Rate Saturation via QFT Approach
Authors: Wu Wei , Jayasuriya Suhada
Published: September 2006

In this paper, a synthesis approach for input rate saturation compensation of feedback systems is presented. Uncertain, stable plants of type greater than or equal to 1 are considered. Based on Horowitz’s original design for input amplitude saturation (Horowitz, I., 1983) and extensions developed in (Wu, W., and Jayasuriya, S., 1999; Wu, W., and Jayasuriya, S., 2001; Wu, W., 2000) an independent loop around the rate saturating element is introduced for saturation compensation by means of the third DOF (degree of freedom) saturation compensator, H(s). First, the structure of the additional loop transmission is constructed to generate the desired response behavior on a systems recovery from saturation. Second, robust stability and robust performance under the addition of H(s) are investigated. The circle criterion, describing function, and nonovershooting conditions are utilized to generate design constraints. In the end, all design constraints involving saturation compensation are expressed as frequency domain bounds, and the synthesis of saturation compensator H(s) follows from loop shaping methods such as QFT. The proposed approach guarantees input/output stability under saturation for the plant class considered.
A Hierarchical Approach to Manipulator Velocity Field Control Considering Dynamic Friction Compensation
Authors: Moreno-Valenzuela Javier , Kelly Rafael
Published: September 2006

The velocity field control of robot manipulators is addressed in this paper. The proposed algorithm has a hierarchical structure based on a velocity field kinematic control scheme for joint velocity resolution and an inner loop of joint velocity control that uses an observer for friction compensation. Experiments on a two degrees-of-freedom direct-drive arm illustrate the performance of the proposed controller.
Adaptive Estimation of Time-Varying Parameters in Linearly Parametrized Systems
Authors: Zhu Yongliang , Pagilla Prabhakar R.
Published: September 2006

Adaptive estimation of time-varying parameters in linearly parametrized systems is considered. The estimation time is divided into small intervals; in each interval the time-varying parameter is approximated by a time polynomial with unknown coefficients. A condition for resetting of the parameter estimate at the beginning of each interval is derived; the condition guarantees that the estimate of the time-varying parameter is continuous and also allows for the coefficients of the polynomial to be different in various time intervals. A modified version of the least-squares algorithm is provided to estimate the time-varying parameters. Stability of the proposed algorithm is shown and discussed. Simulation results on an example are given to validate the proposed method.
Sampled-data Control of a Class of Nonlinear Flat Systems With Application to Unicycle Trajectory Tracking
Authors: Léchevin N. , Rabbath C. A.
Published: September 2006

In this paper we propose a flatness-based nonlinear sampled-data control approach for the trajectory tracking of nonlinear differentially flat systems that can be expressed in cascade form. The nonlinear sampled-data control method relies on the flatness property for the generation of appropriate trajectories, with the design of one-step predictive control laws, and on controller discretization by means of an averaging-like method. In the paper we demonstrate that the causality problem that might arise in the implementation is avoided by using an estimator based on numerical integration techniques of sufficiently high order. Stability-like properties are proved. Numerical simulations show that the proposed sampled-data control law offers the best closed-loop performance when compared with nonlinear direct digital design for the trajectory tracking of a rotorcraft-like UAV modeled as the unicycle. The synthesis of the nonlinear sampled-data control law takes advantage of the feedback linearizability property of the unicycle model. Furthermore, the proposed nonlinear sampled-data control does not rely on approximated discretization techniques and is computed from exponentially convergent steering trajectories that result from the stabilization of the linearized unicycle model.
Model Based Analysis and Control Design of a Urea-SCR deNOx Aftertreatment System
Authors: Upadhyay Devesh , Van Nieuwstadt Michiel
Published: September 2006

In this paper we tackle issues relevant to model based control design for a Urea based Selective Catalytic Reduction (SCR) process relevant to automotive applications. A three state, control oriented, lumped parameter model of the system is used to investigate essential controllability and observability properties of the Urea-SCR plant. Results from the controllability and observability analysis of both nonlinear and linearized models are shown to have realistic implications. Observer design for predicting gas phase ammonia slip is outlined and results presented. An altered definition of the catalyst efficiency is used in control design. It is shown that this altered definition lends itself readily to control synthesis in the Sliding Mode framework while satisfying the dual control objectives of maximizing NOx reduction and minimizing ammonia slip.
Suboptimal Bilinear Routh Approximant for Discrete Systems
Authors: Choo Younseok
Published: September 2006

Recently an improved bilinear Routh approximation method has been suggested for the order reduction of discrete systems. In the method, the last α and β parameters of a reduced model were replaced by new parameters so that the impulse response energy of an original system is also preserved in the reduced model without destroying the stability preserving and time-moments matching properties. In this paper a new and simple improvement is proposed from which one can find a suboptimal bilinear Routh approximant. Compared to the previous result, the approach of this paper has an advantage that the improvement is always guaranteed.
Unsteady Flow Structure and Global Variables in a Centrifugal Pump
Authors: González José , Santolaria Carlos
Published: September 2006

A relationship between the global variables and the dynamic flow structure numerically obtained for a low specific speed centrifugal pump is presented in this paper. A previously developed unsteady flow model is used to correlate the dynamic field with the flow characteristics inside the impeller and volute of a single-stage commercial pump. Actually, the viscous incompressible Navier-Stokes equations are solved within a 3D unsteady flow model. A sliding mesh technique is applied to take into account the impeller-volute interaction. After the numerical model has been successfully compared with the experimental data for the unsteady pressure fluctuations pattern in the volute shroud, a new step is proposed in order to correlate the observed effects with the flow structure inside the pump. In particular, the torque as a function of the relative position of the impeller blades is related to the blades loading, and the secondary flow in the volute is related to the different pressure patterns numerically obtained. Local flow analysis and qualitative study of the helicity in different volute sections is performed. The main goal of the study presented is the successful correlation of local and global parameters for the flow in a centrifugal pump. The pressure forces seem to be the main driven mechanism to establish the flow features both in the impeller and volute, for a wide range of operating conditions.
Measurement of Permeability and Slip Coefficient of Porous Tubes
Authors: Brown N. M. , Lai F. C.
Published: September 2006

Experiments have been conducted to measure the permeability and slip coefficient of seven porous tubes. They were made from fiberglass and nylon nettings with various wall thicknesses. Tests show that these tubes have a distinct permeability in the longitudinal and radial directions. In addition, the slip coefficient which is important in many applications was determined. From the results obtained, one can conclude that both permeabilities depend on the material, but the radial permeability also depends on the wall thickness. The slip coefficient depends not only on the material but also on the Reynolds number, permeabilities, and wall thickness.
Hybrid Particle/Grid Method for Predicting Motion of Micro- and Macrofree Surfaces
Authors: Ishii Eiji , Ishikawa Toru , Tanabe Yoshiyuki
Published: September 2006

We developed a method of hybrid particle/cubic interpolated propagation (CIP) to predict the motion of micro- and macrofree surfaces within gas-liquid flows. Microfree surfaces (smaller than the grid sizes) were simulated with the particle method, and macrofree surfaces (larger than the grid sizes) were simulated with the grid method (CIP is a kind of grid method). With the hybrid, velocities given by the advection part of the particle method were combined with those given by the advection part of CIP. Furthermore, the particles used with the particle method were assigned near the macrofree surfaces by using the volume fraction of liquid that was calculated with CIP. The method we developed was used to predict the collapse of a liquid column. Namely, it was simultaneously able to predict both large deformation in the liquid column and its fragmentation, and the predicted configurations for the liquid column agreed well with the experimentally measured ones. It was also used to predict the behavior of liquid films at the outlet of a fuel injector used for automobile engines. The particle method in the simulation was mainly used for liquid films in the air region and the grid method was used for the other regions to shorten the computational time. The predicted profile of the liquid film was very sharp in the air region where the liquid film became thinner than the grid sizes; there was no loss of liquid film with numerical diffusion.
Hydrofoil Drag Reduction by Partial Cavitation
Authors: Amromin Eduard , Kopriva Jim , Arndt Roger E. A. , Wosnik Martin
Published: September 2006

Partial cavitation reduces hydrofoil friction, but a drag penalty associated with unsteady cavity dynamics usually occurs. With the aid of inviscid theory a design procedure is developed to suppress cavity oscillations. It is demonstrated that it is possible to suppress these oscillations in some range of lift coefficient and cavitation number. A candidate hydrofoil, denoted as OK-2003, was designed by modification of the suction side of a conventional NACA-0015 hydrofoil to provide stable drag reduction by partial cavitation. Validation of the design concept with water tunnel experiments has shown that the partial cavitation on the suction side of the hydrofoil OK-2003 does lead to drag reduction and a significant increase in the lift to drag ratio within a certain range of cavitation number and within a three-degree range of angle of attack. Within this operating regime, fluctuations of lift and drag decrease down to levels inherent to cavitation-free flow. The favorable characteristics of the OK-2003 are compared with the characteristics of the NACA-0015 under cavitating conditions.
Resistance and Fluctuating Pressures of a Large Elbow in High Reynolds Numbers
Authors: Shiraishi Tadashi , Watakabe Hisato , Sago Hiromi , Konomura Mamoru , Yamaguchi Akira , Fujii Tadashi
Published: September 2006

For the Japan Atomic Energy Agency sodium-cooled fast reactor, an experimental study on the fluctuating pressure of the hot legs was carried out with tests in a 1/3-scale model. The total resistance coefficient is consistent with published data, and, additionally, our research has given data up to the Reynolds number of 8.0×106. The flow visualization and velocity measurement confirmed the independence of the flow on the Reynolds number. Pressures on the pipe wall were statistically examined to predict the characteristics of fluctuating pressures of the hot legs. It reveals that generation of fluctuating pressure is dominant on the boundary of flow separation and reattachment.
A Computational Study of Torque and Forces Due to Compressible Flow on a Butterfly Valve Disk in Mid-stroke Position
Authors: Leutwyler Zachary , Dalton Charles
Published: September 2006

The ability to accurately predict the aerodynamic torque and lift and drag forces on a 2-D model of a 0.18 aspect ratio biconvex circular-arc disk operating in a compressible flow using computational fluid dynamics (CFD) was investigated. Fluent 6.0 was the CFD package utilized to perform these calculations. Grid-convergence and time-convergence/stability were analyzed first, followed by a qualitative study of the Spalart-Allmaras, k-ε, and k-ω turbulence models with their enhancement features and model variants. Fluent was used to predict the pressure profile on the disk surface for disk positions 30, 45, and 60 deg (where 0 deg is the fully closed position) and over a range of pressure ratios. The pressure ratios were selected to determine the capability of CFD to accurately predict the flow field and resulting torque in flows ranging from nearly incompressible to highly compressible. Fluent predictions for the pressure profiles on the disk were compared to test data so that the lift and drag forces and aerodynamic torque could be determined responsibly. Acceptable comparisons were noted.
Effects of Curvature and Convective Heat Transfer in Curved Square Duct Flows
Authors: Mondal R. N. , Kaga Y. , Hyakutake T. , Yanase S.
Published: September 2006

Non-isothermal flows with convective heat transfer through a curved duct of square cross section are numerically studied by using a spectral method, and covering a wide range of curvature, δ, 0<δ≤0.5 and the Dean number, Dn, 0≤Dn≤6000. A temperature difference is applied across the vertical sidewalls for the Grashof number Gr=100, where the outer wall is heated and the inner one cooled. Steady solutions are obtained by the Newton-Raphson iteration method and their linear stability is investigated. It is found that the stability characteristics drastically change due to an increase of curvature from δ = 0.23 to 0.24. When there is no stable steady solution, time evolution calculations as well as their spectral analyses show that the steady flow turns into chaos through periodic or multi-periodic flows if Dn is increased no matter what δ is. The transition to a periodic or chaotic state is retarded with an increase of δ. Nusselt numbers are calculated as an index of horizontal heat transfer and it is found that the convection due to the secondary flow, enhanced by the centrifugal force, increases heat transfer significantly from the heated wall to the fluid. If the flow becomes periodic and then chaotic, as Dn increases, the rate of heat transfer increases remarkably.
Design Optimization of Micro Synthetic Jet Actuator for Flow Separation Control
Authors: Baysal Oktay , Köklü Mehti , Erbaş Nurhak
Published: September 2006

A computational analysis and design methodology is presented for effective microflow control using synthetic jets. The membrane is modeled as a moving boundary to accurately compute the flow inside the jet cavity. Compressible Navier-Stokes equations are solved with boundary conditions for the wall slip and the temperature jump conditions encountered for a specific range of Knudsen numbers. For validation, microchannel flow and microfilter flow are successfully computed. Then, flow past a backward-facing step in a microchannel is considered. Analysis is coupled with a design methodology to improve the actuator effectiveness. The objective function is selected to be the square of the vorticity (enstrophy) integrated over a separated region. First, from a design of experiments study, orifice and actuator cavity widths are identified as the most effective design variables. Then, a response surface method is constructed to find the improved control of the flow. This optimization results in more than 83% reduction of the enstrophy of the recirculation region.
Experimental Study of the Flow in a Simulated Hard Disk Drive
Authors: Barbier Charlotte , Humphrey Joseph A. C. , Maslen Eric
Published: September 2006

Instantaneous circumferential and radial velocity components of the air flowing past a symmetrical pair of suspension/slider-units (SSUs) attached to an E-Block/arm were measured in a specially designed corotating disk apparatus simulating a hard disk drive (HDD) using the particle image velocimetry technique. The geometrical dimensions of the components in the apparatus test section were scaled up by a factor of two, approximately, relative to those of a nominal 312 inch HDD. Most of the measurements were obtained on the interdisk midplane for two angular orientations of the arm/SSUs: (a) One with the tip of the SSUs near the hub supporting the disks; (b) another with the tip of the SSUs near the rims of the disks. Data obtained for disk rotational speeds ranging from 250 to 3000rpm (corresponding to 1250 to 15,000rpm, approximately, in a 312 inch HDD) were post-processed to yield mean and rms values of the two velocity components and of the associated shear stress, the mean axial vorticity, and the turbulence intensity (based on the two velocity components). At the locations investigated near the arm/SSUs, and for disk rotational speeds larger than 1500rpm, the mean velocity components are found to be asymptotically independent of disk speed of rotation but their rms values appear to still be changing. At two locations 90 and 29deg, respectively, upstream of the arm/SSUs, the flow approaching this obstruction displays features that can be attributed to the three-dimensional wake generated by the obstruction. Also, between these two locations and depending on the angular orientation of the arm/SSUs, the effect of the obstruction is to induce a three-dimensional region of flow reversal adjacent to the hub. Notwithstanding, the characteristics of the flow immediately upstream and downstream of the arm/SSUs appear to be determined by local flow-structure interactions. Aside from their intrinsic fundamental value, the data serve to guide and test the development of turbulence models and numerical calculation procedures for predicting this complex class of confined rotating flows, and to inform the improved design of HDDs.
The Instability of Shear Thinning and Shear Thickening Spiralling Liquid Jets: Linear Theory
Authors: Uddin J. , Decent S. P. , Simmons M. J.
Published: September 2006

The linear instability of a power law liquid emerging as a jet from an orifice on the surface of a rotating container is investigated, with applications to industrial prilling. Asymptotic methods are used to examine the growth rate and wavenumber of the most unstable traveling wave mode for different flow index numbers. Comparison with Newtonian liquids show that for small rotation rates shear thinning liquids are most stable to disturbances. In contrast for higher rotation rates we find shear thickening liquids are more stable than shear thinning liquids. The influence of viscosity, surface tension, and rotation rate on the growth rates and most unstable wavenumbers associated with both types of liquids are also examined.
Numerical Study of Active Flow Control for a Transitional Highly Loaded Low-Pressure Turbine
Authors: Rizzetta Donald P. , Visbal Miguel R.
Published: September 2006

Active control was simulated numerically for the subsonic flow through a highly loaded low-pressure turbine. The configuration approximated cascade experiments that were conducted to investigate a reduction in turbine stage blade count, which can decrease both weight and mechanical complexity. At a nominal Reynolds number of 25,000 based upon axial chord and inlet conditions, massive separation occurred on the suction surface of each blade due to uncovered turning. Vortex generating jets were then used to help mitigate separation, thereby reducing wake losses. Computations were performed using both steady blowing and pulsed mass injection to study the effects of active flow control on the transitional flow occurring in the aft-blade and near-wake regions. The numerical method utilized a centered compact finite-difference scheme to represent spatial derivatives, that was used in conjunction with a low-pass Pade-type nondispersive filter operator to maintain stability. An implicit approximately factored time-marching algorithm was employed, and Newton-like subiterations were applied to achieve second-order temporal accuracy. Calculations were carried out on a massively parallel computing platform, using domain decomposition to distribute subzones on individual processors. A high-order overset grid approach preserved spatial accuracy in locally refined embedded regions. Features of the flowfields are described, and simulations are compared with each other, with available experimental data, and with a previously obtained baseline case for the noncontrolled flow. It was found that active flow control was able to maintain attached flow over an additional distance of 19–21% of the blade chord, relative to the baseline case, which resulted in a reduction of the wake total pressure loss coefficient of 53–56%.
Detection of Partial Blockages in a Branched Piping System by the Frequency Response Method
Authors: Mohapatra Pranab K. , Chaudhry M. Hanif , Kassem Ahmed , Moloo Jamaluddin
Published: September 2006

Steady oscillatory flow in a branched piping system with partial blockages is studied by using the frequency response method. The peak pressure frequency diagrams at the downstream end are developed with the partial blockage at different locations in the system by using the transfer matrix method. A systematic procedure is presented to estimate the size and the location of a single partial blockage in the system. For more than one partial blockage, it is observed that there is a definite relationship between the frequency responses of the individual and combined partial blockages.
Predictions of Charge Drift in a Concept Electrosprayed DISI Engine
Authors: Nhumaio Geraldo C. S. , Watkins A. Paul
Published: September 2006

Limited to nonvaporizing spray cases, this work discusses the transport of charged droplets within a cylinder of a motored axisymmetric model electrosprayed direct injection spark ignition (eDISI) engine with electrified walls. The concept engine investigated here is assumed to operate with an electrostatic atomizer previously studied for application in fuel burners [Yule et al., 1994, Fuel, 74(7), pp. 1094–1103]. A split/multiple injection strategy is employed in which three pulses of 5mg each are made at crank angles of 80, 150 and 300 deg ATDC of the intake, which fall within the intervals for stable combustion of either early or late injection modes of operation of DISI engines [Jackson et al., 1997, SAE Paper No. 970543]. The direct Simulation Monte Carlo (DSMC) approach embodied in an in-house CFD research code is used to simulate the discrete phase flow with the electrical charge distribution for different instants within the computational cells being computed by simple addition of the droplet charges residing in particular cells at particular instants of time. It is shown in the half engine cycle investigated that the use of charged sprays in eDISI engines may help to reduce the in-cylinder wall-wetting phenomenon. In addition, pockets of highest electrical charge are found to populate the region near the spark plug by 345 deg CA, which may be a path for improved combustion efficiency.
THE ELECTRONIC BAND STRUCTURE OF AlN, AlSb, AlAs AND THEIR TERNARY ALLOYS WITH In
Authors: MOHAMMAD REZEK , KATIRCIOĞLU ŞENAY
Published: September 2006

The electronic band structure of AlN , AlSb , AlAs and their ternary alloys with In has been investigated by ETB. The ETB method has been formulated for sp3d2 basis and nearest neighbor interactions of the compounds and its energy parameters have been derived from the results of the present first principles calculations carried on AlN , AlSb and AlAs . It has been found that the present ETB energy parameters can produce the band structure of the compounds and their ternary alloys with In successfully.
PHASE TRANSITIONS IN SELF-GRAVITATING SYSTEMS
Authors: CHAVANIS P. H.
Published: September 2006

We discuss the nature of phase transitions in self-gravitating systems. We show the connection between the binary star model of Padmanabhan, the thermodynamics of stellar systems and the thermodynamics of self-gravitating fermions. We stress the inequivalence of statistical ensembles for systems with long-range interactions, like gravity. In particular, we contrast the microcanonical evolution of stellar systems from the canonical evolution of self-gravitating Brownian particles. At low energies, self-gravitating Hamiltonian systems experience a gravothermal catastrophe in the microcanonical ensemble. At low temperatures, self-gravitating Brownian systems experience an isothermal collapse in the canonical ensemble. For classical particles, the gravothermal catastrophe leads to a binary star surrounded by a hot halo while the isothermal collapse leads to a Dirac peak containing all the mass. For self-gravitating fermions, the collapse stops when quantum degeneracy comes into play through the Pauli exclusion principle. The end-product of the collapse is a fermion ball, resembling a cold white dwarf star, surrounded by a halo. We can thus describe a phase transition from a gaseous phase to a condensed phase. At high energies or high temperatures, the condensate can experience an explosion, reverse to the collapse, and return to the gaseous phase. Due to the existence of long-lived metastable states, the points of collapse and explosion differ. This leads to a notion of hysteretic cycle in microcanonical and canonical ensembles.