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R Calhoun

Publications and source records attributed to R Calhoun.

10 recordsLinked to original sources
PubMed2006

Paramagnetic particles and mixing in micro-scale flows.

Mixing in microscale flows with rotating chains of paramagnetic particles can be enhanced by adjusting the ratio of viscous to magnetic forces so that chains dynamically break and reform. Lattice Boltzmann (LB) simulations were used to calculate the interaction between the fluid and suspended paramagnetic particles under the influence of a rotating magnetic field. Fluid velocities obtained from the LB simulations are used to solve the advection diffusion equation for massless tracer particles. At relatively high Mason numbers, small chains result in low edge velocities, and hence mixing is slower than at other Mason numbers. At low Mason numbers, long, stable chains form and produce little mixing toward the center of the chains. A peak in mixing rate is observed when chains break and reform. The uniformity of mixing is greater at higher Mason numbers because more small chains result in a larger number of small mixing areas.

Algorithms↗
PubMed2006

Dynamics of rotating paramagnetic particles simulated by lattice Boltzmann and particle dynamics methods.

Novel biochemical sensors consisting of rotating chains of microscale paramagnetic particles have been proposed that would enable convenient, sensitive analyte detection. Predicting the dynamics of these particles is required to optimise their design. The results of lattice Boltzmann (LB) and particle dynamics (PD) simulations are reported, where the LB approach provides a verified solution of the complete Navier-Stokes equations, including the hydrodynamic interactions among the particles. On the other hand, the simpler PD approach neglects hydrodynamic interactions, and does not compute the fluid motion. It is shown that macroscopic properties, like the number of aggregated particles, depend only on the drag force and not on the total hydrodynamic force, making PD simulations yield reasonably accurate predictions. Relatively good agreement between the LB and PD simulations, and qualitative agreement with experimental data, are found for the number of aggregated particles as a function of the Mason number. The drag force on a rotating cylinder is significantly different from that on particle chains calculated from both simulations, demonstrating the different dynamics between the two cases. For microscopic quantities like the detailed force distributions on each particle, the complete Navier-Stokes solution, here represented by the LB simulation, is required.

Computer Simulation↗
PubMed1999

Development of bronchiolitis obliterans syndrome despite blood chimerism in human lung transplant recipients.

Bronchiolitis Obliterans Syndrome (BOS) remains the overwhelming obstacle to the success of lung transplantations (LTx). The presence of donor-specific microchimerism (DSM) and its association with lung allograft function is not well defined. To investigate the relationship between chimerism and BOS, blood was obtained from 21 LTx recipients. Genomic DNA was isolated from patient blood, and PCR-based techniques were used to identify recipient and donor HLA-DR. Fifty percent of the LTx recipients with BOS exhibited DSM at "T1" time post transplant, and 40% at one year follow-up (T2). However, 54% exhibited DSM in the BOS-free group at T1, and 44% at T2. Of the BOS-free, DSM-positive patients at T1, 29% developed BOS by T2. In contrast, 50% of BOS-free DSM-negative patients 50% developed BOS (P > 0.05). Double LTx had a higher prevalence of DSM (73%) and a lower prevalence of BOS (46%) than single LTx (50% and 80% respectively, P > 0.05). One-HLA-DR-antigen-matched LTx recipients show a low prevalence of DSM compared to non-matched (P < 0.05). This study demonstrates that the development of BOS in LTx recipients could also occur in the presence of blood chimerism.

Adult↗
PubMed1997

The Kentucky Emergency Medical Services Information System: current progress and future goals.

The Kentucky Emergency Medical Services Information System was formed in 1993 to establish a centralized registry of prehospital and emergency department data. These data can aid individual providers in planning and providing patient services and state planners in systems development and disease surveillance. This article seeks to provide an overview of the system for providers of acute care services in Kentucky, its current capabilities and future goals.

Adult↗
PubMed1996

Pediatric prehospital care: epidemiology of use in a predominantly rural state.

The objective of this study was to analyze, by retrospective review, the pediatric population utilizing emergency medical services (EMS) throughout Kentucky, with particular emphasis on differences between urban and rural areas. The source of the data used was from all prehospital runs in children less than 17 years of age reported in Kentucky in a computerized database to the state EMS branch. There were no interventions. We found that pediatric calls were more frequent in adolescents than younger children. Trauma was more frequent in older children and in rural settings and accounted for nearly 50% of all calls. Motor vehicle accidents were the most frequent cause of traumatic injuries. Run times were prolonged in the rural setting, but this was a reflection of transport rather than scene times. The use of basic life support (BLS) and advanced life support (ALS) procedures was dependent on the patient's age and the level of care of the provider. ALS procedures were infrequently performed, especially in younger patients, although the performance of these procedures did not prolong scene times. We conclude that educational initiatives for pediatric care in the prehospital setting should include assessment and stabilization of children, including appropriate procedures, both for ALS and BLS providers. Prehospital data should be linked with police reports and emergency department data to provide means of assessing the impact of prehospital services on outcome in pediatric patients.

Adolescent↗
PubMed1996

Development of a statewide trauma system: classification of levels of care available to injured patients.

OBJECTIVE: To categorize the level of care offered in emergency settings at acute care hospitals in Kentucky. DESIGN: Survey mailed to all hospitals in the state. MEASUREMENTS/MAIN RESULTS: Hospital capabilities for both adult and pediatric patients were assessed by strict adherence to a set of preset objective requirements and by a subjective review of the resources available to the acutely injured patient, based on the responses to a mailed questionnaire. There are three level 1 and nine level 2 hospitals available to adults and two level 1 and seven level 2 hospitals available to children in Kentucky. Thirty-five counties are without an acute care hospital. Objective- and subjective-based classification were discordant in approximately 25% of hospitals. Current referral patterns reflect this categorization, but referral is most often directly to level 1 centers. CONCLUSIONS: We have established a set of criteria to categorize the level of care acutely available to injured patients in Kentucky which can be simply implemented. In developing statewide systems of care, strict adherence to preset criteria may not accurately reflect the true resources available. With the lack of a planned and organized system, current referral patterns reflect transfer of patients directly to level 1 centers, which may result in overtriage and underutilization of level 2 or level 3 hospitals.

Adult↗
PubMed1987

Coexistence of gallbladder disease and morbid obesity.

To further investigate the relationship between gallbladder disease and morbid obesity, 92 morbidly obese patients underwent routine cholecystectomy at the time of their bariatric procedures. The preoperative ultrasonographic findings were positive in only 20 patients. Of the 92 patients who underwent cholecystectomy, 87 (95 percent) had pathologic evidence of gallbladder disease. This included cholecystitis, cholesterolosis, cholelithiasis, or some combination of the three. The incidence of postoperative cholecystitis, the technical difficulty of reoperation, the unnecessary expense and exposure to a second hospitalization and a second operation are all completely eliminated when routine cholecystectomy is performed in concert with elective bariatric procedures.

Adult↗