@article{zhang_kleinstreuer_hyun_2012, title={Size-change and deposition of conventional and composite cigarette smoke particles during inhalation in a subject-specific airway model}, volume={46}, ISSN={["1879-1964"]}, DOI={10.1016/j.jaerosci.2011.12.002}, abstractNote={In light of the established health risks of cigarette smoking, less harmful cigarettes (or potential reduced exposure products (PREPs)) have been marketed. Thus, it is of interest to analyze and compare the inhaled droplet dynamics of conventional and new composite cigarette smoke particles (CSPs). Inhalation pattern, hygroscopic growth and deposition of different composite cigarette smoke particles (CSPs) have been simulated numerically in a subject-specific human respiratory airway model from the mouth to generation G9. The validated computer model has been developed to consider the interaction of different deposition mechanisms, including impaction, sedimentation, diffusion, hygroscopic growth, coagulation, as well as possible cloud motion under different exposure and steady breathing conditions (e.g., puffing, post-puffing and two-step inhalation). The computer simulation results are consistent with numerous in-vivo and in-vitro studies as well as whole-lung modeling for deposition of conventional CSPs including hygroscopic growth and cloud motion. It is demonstrated that changes in cigarette composition significantly influence the hygroscopic growth of CSPs. In general, the growth rate of new composite CSPs is larger than the conventional one if the initial water mole-fraction is lower in the droplet. Hygroscopic growth of the new composite CSPs is not a significant mechanism leading to elevated deposition in the oral and tracheobronchial (TB) airways, provided that the relative humidity in the lungs does not exceed 99.5% and the droplet size does not exceed 3 μm; however, enhanced deposition may occur if the particles can grow over 3 μm. In this case, the deposition patterns of CSPs may be controlled by changing the primary composition, especially the initial ratio of water and glycerol. The simulation data with cloud diameters of 0.15–0.2 cm in the oral cavity and 0.5–0.6 cm in the trachea closely match the in-vivo lung deposition measurements of highly dense (conventional) CSPs. Specifically, preferred deposition occurs in the upper airway region, i.e., from the oral cavity to the second bifurcation, with deposition fractions of about 13–22% from the oral cavity to the larynx and 40–57% in the TB airways. This study is helpful for quantitatively evaluating the dose-exposure and subsequent health effects of both conventional and potentially less-harmful cigarettes.}, journal={JOURNAL OF AEROSOL SCIENCE}, author={Zhang, Zhe and Kleinstreuer, Clement and Hyun, Sinjae}, year={2012}, month={Apr}, pages={34–52} }
 @article{hyun_kleinstreuer_longest_chen_2004, title={Particle-hemodynamics simulations and design options for surgical reconstruction of diseased carotid artery bifurcations}, volume={126}, ISSN={["1528-8951"]}, DOI={10.1115/1.1688777}, abstractNote={Based on the hypothesis that aggravating hemodynamic factors play a key role in the onset of arterial diseases, the methodology of “virtual prototyping” of branching blood vessels was applied to diseased external carotid artery (ECA) segments. The goals were to understand the underlying particle-hemodynamics and to provide various geometric design options for improved surgical reconstruction based on the minimization of critical hemodynamic wall parameters (HWPs). First, a representative carotid artery bifurcation (CAB) and then CABs with stenosed ECAs, i.e., a distally occluded ECA and an ECA stump, were analyzed based on transient three-dimensional blood flow solutions, employing a user-enhanced commercial finite volume code. Specifically, the HWPs, i.e., oscillatory shear index, wall shear stress angle gradient, near-wall residence time of monocytes, and near-wall helicity angle difference were evaluated to compare the merits of each design option, including a reconstructed near-optimal junction which generates the lowest HWP-values. The results provide physical insight to the biofluid dynamics of branching blood vessels and guide vascular surgeons as well as stent manufacturers towards interventions leading to high sustained patency rates.}, number={2}, journal={JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME}, author={Hyun, S and Kleinstreuer, C and Longest, PW and Chen, C}, year={2004}, month={Apr}, pages={188–195} }
 @article{buchanan_kleinstreuer_hyun_truskey_2003, title={Hemodynamics simulation and identification of susceptible sites of atherosclerotic lesion formation in a model abdominal aorta}, volume={36}, ISSN={["1873-2380"]}, DOI={10.1016/S0021-9290(03)00088-5}, abstractNote={Employing the rabbit's abdominal aorta as a suitable atherosclerotic model, transient three-dimensional blood flow simulations and monocyte deposition patterns were used to evaluate the following hypotheses: (i) simulation of monocyte transport through a model of the rabbit abdominal aorta yields cell deposition patterns similar to those seen in vivo, and (ii) those deposition patterns are correlated with hemodynamic wall parameters related to atherosclerosis. The deposition pattern traces a helical shape down the aorta with local elevation in monocyte adhesion around vessel branches. The cell deposition pattern was altered by an exercise waveform with fewer cells attaching in the upper abdominal aorta but more attaching around the renal orifices. Monocyte deposition was correlated with the wall shear stress gradient and the wall shear stress angle gradient. The wall stress gradient, the wall shear stress angle gradient and the normalized monocyte deposition fraction were correlated with the distribution of monocytes along the abdominal aorta and monocyte deposition is correlated with the measured distribution of monocytes around the major abdominal branches in the cholesterol-fed rabbit. These results suggest that the transport and deposition pattern of monocytes to arterial endothelium plays a significant role in the localization of lesions.}, number={8}, journal={JOURNAL OF BIOMECHANICS}, author={Buchanan, JR and Kleinstreuer, C and Hyun, S and Truskey, GA}, year={2003}, month={Aug}, pages={1185–1196} }
 @article{loh_hyun_ro_kleinstreuer_2002, title={Acoustic streaming induced by ultrasonic flexural vibrations and associated enhancement of convective heat transfer}, volume={111}, ISSN={["0001-4966"]}, DOI={10.1121/1.1433811}, abstractNote={Acoustic streaming induced by ultrasonic flexural vibrations and the associated convection enhancement are investigated. Acoustic streaming pattern, streaming velocity, and associated heat transfer characteristics are experimentally observed. Moreover, analytical analysis based on Nyborg’s formulation is performed along with computational fluid dynamics (CFD) simulation using a numerical solver CFX 4.3. Two distinctive acoustic streaming patterns in half-wavelength of the flexural vibrations are observed, which agree well with the theory. However, acoustic streaming velocities obtained from CFD simulation, based on the incompressible flow assumption, exceed the theoretically estimated velocity by a factor ranging from 10 to 100, depending upon the location along the beam. Both CFD simulation and analytical analysis reveal that the acoustic streaming velocity is proportional to the square of the vibration amplitude and the wavelength of the vibrating beam that decreases with the excitation frequency. It is observed that the streaming velocity decreases with the excitation frequency. Also, with an open-ended channel, a substantial increase in streaming velocity is observed from CFD simulations. Using acoustic streaming, a temperature drop of 40 °C with a vibration amplitude of 25 μm at 28.4 kHz is experimentally achieved.}, number={2}, journal={JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA}, author={Loh, BG and Hyun, S and Ro, PI and Kleinstreuer, C}, year={2002}, month={Feb}, pages={875–883} }
 @article{hyun_kleinstreuer_archie_2001, title={Computational particle-hemodynamics analysis and geometric reconstruction after carotid endarterectomy}, volume={31}, ISSN={["0010-4825"]}, DOI={10.1016/S0010-4825(01)00007-5}, abstractNote={Transient three-dimensional laminar incompressible dilute suspension flow in rigid in-plane carotid artery bifurcations has been solved with a user-enhanced finite-volume program. Instantaneous velocity vector and wall shear stress vector fields illustrate strong "disturbed flow" patterns. Implications of elevated surface contours of hemodynamic wall parameters, indicating such disturbed flows, and particle deposition sites are discussed and a relative comparison in terms of indicator functions between the endarterectomized carotid artery bifurcation and two design improvements is shown. Although the combined perioperative mortality and non-fatal stroke rate for carotid endarterectomy ranges only from 2% to 7%, the final geometric design recommendation presented merits consideration because it may significantly lower the chances of post-operative complications such as stroke, ischemic attack, or even death. The new carotid artery bifurcation design is based on the overall reduction of "disturbed flow" indicator functions, including the time-averaged wall shear stress angle deviation and a wall deposition parameter for critical blood particles, such as monocytes.}, number={5}, journal={COMPUTERS IN BIOLOGY AND MEDICINE}, author={Hyun, S and Kleinstreuer, C and Archie, JP}, year={2001}, month={Sep}, pages={365–384} }
 @article{kleinstreuer_hyun_buchanan_longest_archie_truskey_2001, title={Hemodynamic parameters and early intimal thickening in branching blood vessels}, volume={29}, DOI={10.1615/critrevbiomedeng.v29.i1.10}, abstractNote={Intimal thickening due to atherosclerotic lesions or intimal hyperplasia in medium to large blood vessels is a major contributor to heart disease, the leading cause of death in the Western World. Balloon angioplasty with stenting, bypass surgery, and endarterectomy (with or without patch reconstruction) are some of the techniques currently applied to occluded blood vessels. On the basis of the preponderance of clinical evidence that disturbed flow patterns play a key role in the onset and progression of atherosclerosis and intimal hyperplasia, it is of interest to analyze suitable hemodynamic wall parameters that indicate susceptible sites of intimal thickening and/or favorable conditions for thrombi formation. These parameters, based on the wall shear stress, wall pressure, or particle deposition, are applied to interpret experimental/clinical observations of intimal thickening. Utilizing the parameters as "indicator" functions, internal branching blood vessel geometries are analyzed and possibly altered for different purposes: early detection of possibly highly stenosed vessel segments, prediction of future disease progression, and vessel redesign to potentially improve long-term patency rates. At the present time, the focus is on the identification of susceptible sites in branching blood vessels and their subsequent redesign, employing hemodynamic wall parameters. Specifically, the time-averaged wall shear stress (WSS), its spatial gradient (WSSG), the oscillatory shear index (OSI), and the wall shear stress angle gradient (WSSAG) are compared with experimental data for an aortoceliac junction. Then, the OSI, wall particle density (WPD), and WSSAG are segmentally averaged for different carotid artery bifurcations and compared with clinical data of intimal thickening. The third branching blood vessel under consideration is the graft-to-vein anastomosis of a vascular access graft. Suggested redesigns reduce several hemodynamic parameters (i.e., the WSSG, WSSAG, and normal pressure gradient [NPG]), thereby reducing the likelihood of restenosis, especially near the critical toe region.}, number={1}, journal={Critical Reviews in Biomedical Engineering}, author={Kleinstreuer, C. and Hyun, S. and Buchanan, J. R. and Longest, P. W. and Archie, J. P. and Truskey, G. A.}, year={2001}, pages={1–64} }
 @article{hyun_kleinstreuer_2001, title={Numerical simulation of mixed convection heat and mass transfer in a human inhalation test chamber}, volume={44}, ISSN={["1879-2189"]}, DOI={10.1016/S0017-9310(00)00268-4}, abstractNote={Large baffled rectangular chambers, Rochester-style test chambers, and displacement ventilated rooms have traditionally been used to study effects of potentially toxic pollutants on animals and humans. Recently, the interest in harmful effects of indoor gaseous pollutants and associated air quality control have rapidly increased because most urban dwellers spend more than 90% of their daily lives in closed environments. Of interest here are the experimentally validated CFD simulations of transient turbulent non-isothermal flow with tracer gas transport in a personal exposure environment. The purpose of this paper is to examine the effect of transient breathing on trace gas ambient (i.e., exposure) concentrations and ultimately the uptake (i.e., dose concentrations) by the subject for three different orientations with respect to the non-isothermal air stream and the location of the tracer gas source.}, number={12}, journal={INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER}, author={Hyun, S and Kleinstreuer, C}, year={2001}, month={Jun}, pages={2247–2260} }
 @article{comer_kleinstreuer_hyun_kim_2000, title={Aerosol transport and deposition in sequentially bifurcating airways}, volume={122}, ISSN={["1528-8951"]}, DOI={10.1115/1.429636}, abstractNote={Deposition patterns and efficiencies of a dilute suspension of inhaled particles in three-dimensional double bifurcating airway models for both in-plane and 90 deg out-of-plane configurations have been numerically simulated assuming steady, laminar, constant-property air flow with symmetry about the first bifurcation. Particle diameters of 3, 5, and 7 μm were used in the simulation, while the inlet Stokes and Reynolds numbers varied from 0.037 to 0.23 and 500 to 2000, respectively. Comparisons between these results and experimental data based on the same geometric configuration showed good agreement. The overall trend of the particle deposition efficiency, i.e., an exponential increase with Stokes number, was somewhat similar for all bifurcations. However, the deposition efficiency of the first bifurcation was always larger than that of the second bifurcation, while in general the particle efficiency of the out-of-plane configuration was larger than that of the in-plane configuration. The local deposition patterns consistently showed that the majority of the deposition occurred in the carinal region. The distribution pattern in the first bifurcation for both configurations were symmetric about the carina, which was a direct result of the uniaxial flow at the inlet. The deposition patterns about the second carina showed increased asymmetry due to highly nonuniform flow generated by the first bifurcation and were extremely sensitive to bifurcation orientation. Based on the deposition variations between bifurcation levels and orientations, the use of single bifurcation models was determined to be inadequate to resolve the complex fluid–particle interactions that occur in multigenerational airways. [S0148-0731(00)01102-X]}, number={2}, journal={JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME}, author={Comer, JK and Kleinstreuer, C and Hyun, S and Kim, CS}, year={2000}, month={Apr}, pages={152–158} }
 @article{hyun_kleinstreuer_archie_2000, title={Computer simulation and geometric design of endarterectomized carotid artery bifurcations}, volume={28}, ISSN={["0278-940X"]}, DOI={10.1615/critrevbiomedeng.v28.i12.100}, abstractNote={The main goal of this computational study is to establish surgical guidelines for optimal geometries of carotid endarterectomy reconstructions that may measurably reduce postoperative complications, that is, thrombosis, stroke, and/or restenosis. The underlying hypotheses are that nonuniform hemodynamics, or "disturbed flows," are linked to arterial diseases and consequently that minimization of "disturbed flow" indicators leads to geometric bifurcation designs that lower postoperative complication rates. Considering transient 3-D laminar blood flow in partially occluded, in-plane, rigid-wall carotid artery bifurcations, the results presented include time-averaged indicators of "disturbed flow", such as the wall shear stress, spatial wall shear stress gradient, and wall shear stress angle deviation. In addition, trajectories and deposition patterns of critical blood particles (i.e., monocytes) are shown and evaluated. Within given physiological constraints, the vessel geometry was then changed in order to reduce the magnitudes of key indicators associated with thrombosis (i.e., blood clot formation) or restenosis (e.g., renewed atherosclerosis and/or hyperplasia). The quantitative results and knowledge base generated will be crucial for future clinical trials.}, number={1-2}, journal={CRITICAL REVIEWS IN BIOMEDICAL ENGINEERING}, author={Hyun, S and Kleinstreuer, C and Archie, JP}, year={2000}, pages={53–59} }
 @article{hyun_kleinstreuer_archie_2000, title={Hemodynamics analyses of arterial expansions with implications to thrombosis and restenosis}, volume={22}, ISSN={["1350-4533"]}, DOI={10.1016/S1350-4533(00)00006-0}, abstractNote={It is assumed that critical hemodynamic factors play an important role in the onset, localization and degree of post-operative complications, for example, thrombosis and restenosis. Of special interest are sudden expansion flows, which may occur in straight artery segments such as the common carotid after endarterectomy or end-to-end anastomoses. Sudden expansion geometries are possible origins of early post-operative emboli and significant myointimal hyperplasia resulting in early or late complications. Transient laminar axisymmetric and fully three-dimensional blood flows were simulated employing a validated finite volume code in conjunction with a Runge–Kutta particle tracking technique. Disturbed flow indicators, which may predict the onset of thrombosis and/or restenosis, were identified and employed to evaluate 90°-step and smooth expansion geometries. Smooth expansion geometries have weaker disturbed flow features than step expansion geometries. Specifically, the regions near the expansion wall and the reattachment point are susceptible to both atherosclerotic lesion and thrombi formations as indicated by non-uniform hemodynamic indicators such as near-zero wall shear stress and elevated wall shear stress gradients as well as blood particle accumulation and deposition. A new parameter, the wall shear stress angle deviation (WSSAD) has been introduced, which indicates areas of abnormal endothelial cell morphology and particle wall deposition. In turn, regions of low wall shear stress and high wall shear stress gradients are recognized as susceptible sites for arterial diseases. Thus, it is interesting to note that high WSSAD surface areas cover low wall shear stress, high wall shear stress gradient locations as well as high wall particle deposition. A gradual change in step expansion geometry provides better results in terms of WSSAD values and hence potentially reducing atherosclerosis as well as thrombi formation.}, number={1}, journal={MEDICAL ENGINEERING & PHYSICS}, author={Hyun, S and Kleinstreuer, C and Archie, JP}, year={2000}, month={Jan}, pages={13–27} }