The hydrodynamic characteristics of upflow anaerobic sludge blanket (UASB) reactors were investigated in this study. A UASB reactor was visualized as being set‐up of a number of continuously stirred tank reactors (CSTRs) in series. An increasing‐sized CSTRs (ISC) model was developed to describe the hydrodynamics of such a bioreactor. The gradually increasing tank size in the ISC model implies that the dispersion coefficient decreased along the axial of the UASB reactor and that its hydrodynamic behavior was basically dispersion‐controlled. Experimental results from both laboratory‐scale H2‐producing and full‐scale CH4‐producing UASB reactors were used to validate this model. Simulation results demonstrate that the ISC model was better than the other models in describing the hydrodynamics of the UASB reactors. Moreover, a three‐dimensional computational fluid dynamics (CFD) simulation was performed with an Eulerian‐Eulerian three‐phase‐fluid approach to visualize the phase holdup and to explore the flow patterns in UASB reactors. The results from the CFD simulation were comparable with those of the ISC model predictions in terms of the flow patterns and dead zone fractions. The simulation results about the flow field further confirm the discontinuity in the mixing behaviors throughout a UASB reactor. © 2008 American Institute of Chemical Engineers AIChE J, 2009

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Background Involvement of resection margins and the pattern of tumor invasion are reported to be important predictors of local recurrence and survival in surgically treated patients. In this study we have retrospectively assessed the significance of these two prognostic factors in a relatively homogeneous patient population. Patients and Methods This study was confined to 150 previously untreated patients who had surgery for squamous carcinoma of the oral tongue between 1987 and 1993. There were 82 men and 68 women who ranged in age from 25 to 89 years (median 60 years). Glossectomy was peroral in 129, whereas 8 and 13, respectively, had a cheek flap or mandibulotomy approach. Some form of lymphadenectomy was performed in 109 (73%), and 51 patients (34%) received postoperative radiotherapy. Histologic slides from each primary tumor were reviewed to verify the margin status. In addition, the pattern of invasion was evaluated and graded from 1 to 4, varying from a consistently well‐defined, “pushing” border (Grade 1) to diffuse infiltration and cellular dissociation (Grade 4). Results Intraoperative frozen section assessment of margins was accurate, whether positive or negative, in 118 of 133 patients (89%). Positive or close margins (within one high‐power field) and an endophytic growth pattern were associated with a significant increase in local recurrence (p <0.003 and <0.04, respectively). With higher grades of infiltration (Grade 3 or 4; 82 patients), the tumors tended to be larger and the patients younger. Although the likelihood of nodal involvement and subsequent distant metastasis was significantly greater in those with Grade 3 or grade 4 patterns (p <0.0003 and <0.01, respectively), there was no impact on local recurrence. Cumulative survival was similar whether or not the surgical margins were involved, but was significantly reduced when the pattern of tumor invasion was of higher grade (p <0.01). Summary Frozen section provided reasonably accurate information about margins in our patients, whether taken from the patient or the surgical specimen. Positive margins increased the likelihood of local recurrence, but did not impact on survival because subsequent surgery and/or irradiation controlled tumor recurrence in some patients. Grade 3 or 4 patterns at the tumor/host interface were associated with an increased incidence of nodal and distant metastasis, as well as a significant decrease in survival. © 1999 John Wiley & Sons, Inc. Head Neck 21: 408–413, 1999.

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