589 results for Chase, J.G.

  • Continuous Glucose Monitors and Tight Glycaemic Control in Intensive Care: An In-Silico Proof of Concept Analysis

    Signal, M.; Pretty, C.G.; LeCompte, A.J.; Shaw, G.M.; Chase, J.G. (2010)


    University of Canterbury Library

    Tight glycaemic control (TGC) in critical care has shown distinct benefits, but has also proven difficult to obtain. The risk of severe hypoglycaemia (< 2.2mmol/L) raises significant concerns for safety. Continuous Glucose Monitors (CGMs) offer frequent, though potentially noisy, automated measurement and thus the possibility of using them for early detection and intervention of hypoglycaemic events. This in-silico study investigates the potential of CGM devices to maintain control, prevent hypoglycaemia and reduce clinical effort. Retrospective clinical data from the SPRINT TGC study covering 26 patients was used with clinically validated metabolic system models and 3 different stochastic noise models (two Gaussian and one first-order autoregressive.) The noisy, virtual CGM blood glucose (BG) values were filtered and used to drive the SPRINT TGC protocol. A simple threshold alarm was used to trigger glucose interventions to avert potential hypoglycaemia. Monte Carlo analysis was used to get robust results from the stochastic noise models. Using SPRINT with simulated CGM noise, the BG time in the 4.4-6.1mmol/L band was reduced no more than 3% from 45.2% obtained with glucometer sensors. The number of patients experiencing severe hypoglycaemia was reduced by 0-30%. Duration of hypoglycaemic events was reduced by 19-65%. Finally, nurse workload was reduced by approximately 20 minutes per patient, per day. The results of this proof of concept study justify a pilot clinical study for verification in a clinical setting.

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  • Rocket Roll Dynamics and Disturbance – Minimal modelling and system identification

    Hann, C.E.; Snowdon, M.; Rao, A.; Tang, R.; Korevaar, A.; Skinner, G.; Keall, A.; Chen, X.Q.; Chase, J.G. (2010)


    University of Canterbury Library

    The roll dynamics of a 5kg, 1.3 m high sounding rocket are analyzed in a vertical wind tunnel. Significant turbulence in the tunnel makes the system identification of the effective inertia, damping and asymmetry with respect to roll challenging. A novel method is developed which decouples the disturbance from the rocket frame’s intrinsic roll dynamics and allows accurate prediction of roll rate and angle. The parameter identification method is integral-based, and treats wind disturbances as equivalent to a movement in the actuator fins. The method is robust, requires minimal computation, and gave a realistic disturbance distribution reflecting the randomness of the turbulent wind flow. The mean absolute roll rate of the rocket frame observed in experiments was 16.4 degree/s and the model predicted the roll rate with a median error of 0.51 degrees/s with a 90th percentile of 1.25 degrees/s. The roll angle (measured by an encoder), was tracked by the model with a median absolute error of 0.25 degrees and a 90th percentile of 0.50 degrees. These results prove the concept of this minimal modeling approach which will be extended to pitch and yaw dynamics in the future.

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  • Modeled Insulin Sensitivity and Interstitial Insulin Action from a Pilot Study of Dynamic Insulin Sensitivity Tests

    Lin, J.; Jamaludin, U.; Docherty, P.D.; Razak, N.N.; Le Compte, A.J.; Pretty, C.G.; Hann, C.E.; Shaw, G.M.; Chase, J.G. (2010)


    University of Canterbury Library

    An accurate test for insulin resistance can delay or prevent the development of Type 2 diabetes and its complications. The current gold standard test, CLAMP, is too labor intensive to be used in general practice. A recently developed dynamic insulin sensitivity test, DIST, uses a glucose-insulin-C-peptide model to calculate model-based insulin sensitivity, SI. Preliminary results show good correlation to CLAMP. However both CLAMP and DIST ignore saturation in insulin-mediated glucose removal. This study uses the data from 17 patients who underwent multiple DISTs to investigate interstitial insulin action and its influence on modeled insulin sensitivity. The critical parameters influencing interstitial insulin action are saturation in insulin receptor binding, αG, and plasma-interstitial difiusion rate, nI . Very low values of αG and very low values of nI produced the most intra-patient variability in SI. Repeatability in SI is enhanced with modeled insulin receptor saturation. Future parameter study on subjects with varying degree of insulin resistance may provide a better understanding of different contributing factors of insulin resistance.

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  • Glargine as a Basal Insulin Supplement in Recovering Critically Ill Patients - An In Silico Study

    Razak, N.N.; Lin, J.; Chase, J.G.; Shaw, G.M.; Pretty, C.G.; Le Compte, A.J.; Suhaimi, F.M.; Jamaludin, U. (2010)


    University of Canterbury Library

    Tight glycaemic control is now benefiting medical and surgical intensive care patients by reducing complications associated with hyperglycaemia. Once patients leave this intensive care environment, less acute wards do not continue to provide the same level of glycaemic control. Main reason is that these less acute wards do not have the high levels of nursing resources to provide the same level of glycaemic control. Therefore developments in protocols that are less labour intensive are necessary. This study examines the use of insulin glargine for basal supplement in recovering critically ill patients. These patients represent a group who may benefit from such basal support therapy. In silico study results showed the potential in reducing nursing effort with the use of glargine. However, a protocol using only glargine for glucose control did not show to be effective in the simulated patients. This may be an indication that a protocol using only glargine is more suitable after discharge from critical care.

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  • Impact of variation in patient response on model-based control of glycaemia in critically ill patients

    LeCompte, A.J.; Chase, J.G.; Shaw, G.M.; Lin, J.; Lynn, A.; Pretty, C.G. (2010)


    University of Canterbury Library

    Critically ill patients commonly experience stress-induced hyperglycaemia, and several studies have shown tight glycaemic control (TGC) can reduce patient mortality. However, tight control is often difficult to achieve due to conflicting drug therapies and evolving patient condition. Thus, a number of studies have failed to achieve TGC possibly due to use of fixed insulin dosing protocols over adaptive patient-specific methods. Model-based targeted glucose control can adapt insulin and dextrose interventions to match identified patient sensitivity. This study explores the impact on control of assuming patient response to insulin is constant versus time-varying. Simulated trials of glucose control were performed on adult and neonatal virtual patient cohorts. Results indicate assumptions of constant insulin sensitivity can lead to significantly increased rates of hypoglycaemia, a commonly cited issue preventing increased adoption of tight glycaemic control in critical care. It is clear that adaptive, patientspecific, approaches are better able to manage inter- and intra- patient variability than typical, fixed protocols.

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  • Evaluation of the Performances and Costs of a Spectrum of DIST Protocols

    Docherty, P.D.; Chase, J.G.; Lotz, T.F.; Hann, C.E.; TeMorenaga, L.; McAuley, K.A.; Shaw, G.M.; Berkeley, J.E,; Mann, J.I. (2010)


    University of Canterbury Library

    The strategic design of most insulin sensitivity (SI) tests maximises either accuracy or economy, but not both. Hence, accurate, large-scale screening isn’t feasible. The DIST was developed to better optimize both important metrics. The highly flexible DIST protocol samples insulin, glucose and C-peptide during a comparatively short test. Varying the sampling periods and assays, and utilising alternative computational methods enables a wide range of tests with different accuracy and economy tradeoffs. The result is a hierarchy of tests to facilitate low-cost screening. Eight variations of the DIST are evaluated against the fully-sampled test by correlating the SI and endogenous insulin production (Uen(t)) metrics. Five variations include sample and assay reductions and three utilise DISTq parameter estimations. The DISTq identification methods only require glucose assays and thus enable real-time analysis. Three DISTq methods were tested; the fully-sampled, the Short, and the 30 minute two-sample protocol. 218 DIST tests were completed on 84 participants to provide the data for this study. Methods that assayed insulin replicated the findings of the full DIST particularly well (R=0.89~0.92) while those that assayed C-peptide managed to best replicate endogenous insulin metrics (R=0.72~1.0). The three DISTq protocols correlated to the fully-sampled DIST at R=0.83, 0.77 and 0.71 respectively. As expected, test resolution increased with rising protocol cost and intensity. The ability of significantly less expensive tests to replicate the values of the fully-sampled DIST was relatively high (R=0.92 with four glucose and two insulin assays and 0.71 with only two glucose assays). Thus, an SI screening programme could achieve high resolution at a low cost by using a lower resolution DIST test. When an individual’s result is close to a diagnostic threshold stored test samples could be re-assayed for more species to allow a higher resolution analysis without the need for a second invasive clinical test. Hence, a single test can lead to several outcomes with this hierarchy approach, enabling large scale screening with high resolution only where required with minimal and feasible economic cost and only a single invasive clinical procedure.

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  • A Fast and Accurate Diagnostic Test for Severe Sepsis Using Kernel Classifiers

    Parente, J.D.; Lee, D.S.; Lin, J.; Chase, J.G.; Shaw, G.M. (2010)


    University of Canterbury Library

    Severe sepsis occurs frequently in the intensive care unit (ICU) and is a leading cause of admission, mortality, and cost. Treatment guidelines recommend early intervention, however gold standard blood culture test results may return in up to 48 hours. Insulin sensitivity (SI) is known to decrease with worsening condition and inflammatory response, and could thus be used to aid clinical treatment decisions. Some glycemic control protocols are able to accurately identify SI in real-time. A biomarker for severe sepsis was developed from retrospective SI and concurrent temperature, heart rate, respiratory rate, blood pressure, and SIRS score from 36 adult patients with sepsis. Patients were identified as having sepsis based on a clinically validated sepsis score (ss) of 2 or higher (ss = 0–4 for increasing severity). Kernel density estimates were used for the development of joint probability density profiles for ss = 2 and ss < 2 data hours (213 and 5858 respectively of 6071 total hours) and for classification. From the receiver operator characteristic (ROC) curve, the optimal probability cutoff values for classification were determined for in-sample and out-of-sample estimates. A biomarker including concurrent insulin sensitivity and clinical data for the diagnosis of severe sepsis (ss = 2) achieves 69–94% sensitivity, 75–94% specificity, 0.78–0.99 AUC, 3–17 LHR+, 0.06–0.4 LHR-, 9–38% PPV, 99–100% NPV, and a diagnostic odds ratio of 7–260 for optimal probability cutoff values of 0.32 and 0.27 for in-sample and out-of-sample data, respectively. The overall result lies between these minimum and maximum error bounds. Thus, the clinical biomarker shows good to high accuracy and may provide useful information as a real-time diagnostic test for severe sepsis.

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  • Influence Of HF2V Damping Devices On The Performance Of The SAC3 Building Subjected To The SAC Ground Motion Suites

    Rodgers, G.W.; Chase, J.G.; MacRae, G.A.; Bacht, T.; Dhakal, R.P.; Desombre, J. (2010)


    University of Canterbury Library

    Recent advances in energy dissipation for structural systems can create structural connections that undergo zero sacrificial energy absorbing damage, even at extreme story drifts. However, questions exist around the ability of such structures to re-center after a major event. In this paper, the seismic performance of the as-designed SAC LA3 seismic frame with rigid moment connections at the beam ends is compared with the same frame using semi-rigid connections with high force-to-volume (HF2V) lead dissipators. Non-linear dynamic analysis is preformed using Abaqus™. With respect to re-centering, the presence of the gravity frames in the model is also considered. It was found that the placement of dissipators, ignoring the effect of gravity frames, caused a 12% increase in period due to the decreased stiffness of the connections. During design level ground shaking the semi-rigid connections with HF2V dissipators have slightly lower accelerations, up to an 80% increase in peak drift, and a 200% increase in the permanent displacement compared to the as-designed case, but no structural damage is expected. When gravity frames are considered, the floor accelerations decrease further, the peak displacements do not significantly change, but the residual storey drift ratios reduce to approximately 0.17%. This result is less than one half that of the as-designed frame, where typically gravity frame effects are not considered. The addition of braces with a stiffness 20% of the pushover stiffness ensures that the structures can re-center after any given event to within construction error. The realistic non-linear dynamic analyses combining HF2V dissipators with gravity frames and well-designed non-structural elements creates a system with almost no structural damage and low residual displacements.

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  • Intensive Control Insulin-Nutrition-Glucose Model Validated in Critically Ill Patients

    Lin, J.; Razak, N.N.; Pretty, C.G.; LeCompte, A.J.; Docherty, P.D.; Parente, J.D.; Shaw, G.M.; Hann, C.E.; Chase, J.G. (2010)


    University of Canterbury Library

    A comprehensive, more physiologically relevant Intensive Control Insulin-Nutrition- Glucose (ICING) Model is presented and validated using data from critically ill patients. Glucose utilisation and its endogenous production in particular, are more distinctly expressed. A more robust glucose absorption model through ingestion is also added. Finally, this model also includes explicit pathways of insulin kinetics, clearance and utilisation. Identification of critical constant population parameters is carried out parametrically, optimising one hour forward prediction errors, while avoiding model identifiability issues. The identified population values are pG = 0.006 min-1, EGPb = 1.16 mmol/min and nI = 0.003 min-1, all of which are within reported physiological ranges. Insulin sensitivity, SI , is identified hourly for each individual. All other model parameters are kept at well-known population values or functions of body weight or surface area. A sensitivity study confirms the validity of limiting time-varying parameters to SI only. The model achieves median fitting error <1% in data from 173 patients (N = 42,941 hrs in total) who received insulin while in the Intensive Care Unit (ICU) and stayed for more than 72 hrs. Most importantly, the median per patient one-hour ahead prediction error is a very low 2.80% [IQR 1.18, 6.41%]. It is significant that the 75th percentile prediction error is now within the lower bound of typical glucometer measurement errors of 7-12%. This result further confirms that the model is suitable for developing model-based insulin therapies, and capable of delivering tight blood glucose control, in a real-time model based control framework with a tight prediction error range.

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  • Validation of a Model-based Virtual Trials Method for Tight Glycemic Control in Intensive Care

    Suhaimi, F.M.; Chase, J.G.; LeCompte, A.J.; Preiser, J-C,; Lin, J.; Shaw, G.M. (2010)


    University of Canterbury Library

    In-silico virtual trials offer significant advantages in cost, time and safety. However, no such method has been truly validated with clinical data. This study tests 2 matched cohorts from an independent ICU treated with 2 different glycaemic control protocols. The goal is to validate the in-silico virtual trials model and methods, including the underlying assumptions. A retrospective analysis used records from a 211 patient subset of the Glucontrol trial in Liege, Belgium. Glucontrol-A (N = 142) targeted a BG range of 4.4-6.1 mmol/L and Glucontrol-B (N = 69) targeted 7.8-10.0 mmol/L. Cohorts were matched by APACHE II score, but the Glucontrol A cohort was slightly older (p = 0.0352). Results showed high correlation between self- and cross-validation virtual trials and clinical results. The virtual trials models and methods are thus validated on independent data.

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  • Range90 as indicator for ventilator output versus patients demand: NAVA and pressure support for non-invasively ventilated patients

    Chiew, Y.S.; Piquilloud, L.; Lambermont, B.; Roeseler, J.; Revelly, J.P.; Bialais, E.; Tassaux, D.; Jolliet, P.; Chase, J.G.; Desaive, T. (2012)


    University of Canterbury Library

    2-pages

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  • Composite slab effects on beam-column subassemblies: Further development

    Chaudhari, T.; MacRae, G.A.; Bull, D.; Chase, J.G.; Hobbs, M. (2014)


    University of Canterbury Library

    Composite slab construction is gaining popularity in New Zealand. These slabs may influence the beam column joint subassemblies as they exposed to earthquake induced shaking. However several design issues with composite slabs need to be addressed so that they can be used to their full advantage in design. These relate to the ability to consider the slab effect on the beam design strength, the likely statistical variation of beam and slab under strong seismic shocks that will affect the column joint demand and the resistance of the panel zone. In this paper, the experimental test setups are described which considers slab isolation, beam overstrength, full depth slab around the column, low damage connection, and demand on the panel zone. A new concept of slab confinement using a shear key will be presented to form a force transfer mechanism to avoid failure of concrete either in crushing or spalling. Also the development of a non-prying sliding hinge joint low damage connection and its performance under composite slab is discussed. The outcome of this will be useful to develop simple design recommendations for the New Zealand steel standard.

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  • Using "system sensing" during the implementation of a new mechatronics engineering curriculum

    O'Steen, B.; Brogt, E.; Chen, X.; Chase, J.G. (2010)


    University of Canterbury Library

    Virtual presentation 6pages

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  • Using "system sensing" during the implementation of a new mechatronics engineering curriculum

    O'Steen, B.; Brogt, E.; Chen, X.Q.; Chase, J.G. (2010)


    University of Canterbury Library

    Virtual presentation 6pages

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  • Influence Of HF2V Damping Devices On The Performance Of The SAC3 Building Subjected To The SAC Ground Motion Suites

    Rodgers, G.W.; Chase, J.G.; MacRae, G.A.; Bacht, T.; Dhakal, R.P.; Desombre, J. (2010)


    University of Canterbury Library

    Recent advances in energy dissipation for structural systems can create structural connections that undergo zero sacrificial energy absorbing damage, even at extreme story drifts. However, questions exist around the ability of such structures to re-center after a major event. In this paper, the seismic performance of the as-designed SAC LA3 seismic frame with rigid moment connections at the beam ends is compared with the same frame using semi-rigid connections with high force-to-volume (HF2V) lead dissipators. Non-linear dynamic analysis is preformed using Abaqus™. With respect to re-centering, the presence of the gravity frames in the model is also considered. It was found that the placement of dissipators, ignoring the effect of gravity frames, caused a 12% increase in period due to the decreased stiffness of the connections. During design level ground shaking the semi-rigid connections with HF2V dissipators have slightly lower accelerations, up to an 80% increase in peak drift, and a 200% increase in the permanent displacement compared to the as-designed case, but no structural damage is expected. When gravity frames are considered, the floor accelerations decrease further, the peak displacements do not significantly change, but the residual storey drift ratios reduce to approximately 0.17%. This result is less than one half that of the as-designed frame, where typically gravity frame effects are not considered. The addition of braces with a stiffness 20% of the pushover stiffness ensures that the structures can re-center after any given event to within construction error. The realistic non-linear dynamic analyses combining HF2V lead dissipators with gravity frames and well-designed non-structural elements creates a system with almost no structural damage and low residual displacements.

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  • Altered blood glucose dynamics during and after anhepatic phase of liver transplantation: a model-based approach

    Homlok, J.; Chase, J.G.; Benyo, B.; Kovacs, K. (2013)


    University of Canterbury Library

    “© © 2013 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.”

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  • Comparison of model based and clinical blood glucose evolution during and after anhepatic status

    Homlok, J.; Chase, J.G.; Turi, Cs; Benyo, B. (2013)

    Conference Contributions - Other
    University of Canterbury Library

    Blood glucose (BG) control is a major difficulty during liver transplantation (LT). A model-based approach to analysis and control can enhance the efficiency of BG management during LT surgery. An existing clinically validated metabolic model was fitted to data from 8 LT patients. The reperfusion part of the post-anhepatic phase of LT shows a clear consistent dynamic rise in blood glucose (BG) level that would enable better prediction of future BG in this phase. Model fitting errors showed that the fundamental model captured all primary dynamics but parameter adjustment to reflect known conditions during LT surgery in specific phases would improve model quality.

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  • Development and Identification of a Closed-Loop Model of the Cardiovascular System Including the Atria

    Pironet, A.; Revie, J.A.; Paeme, S.; Dauby, P.C.; Chase, J.G.; Desaive, T. (2011)

    Conference Contributions - Published
    University of Canterbury Library

    The atria play an important role in cardiac function. The introduction of two chambers representing the atria in an existing model of the cardiovascular system could provide useful information. A previously validated cardiovascular system model is modified to include the atria, whose behaviour is modelled in an original way. An a-wave pressure independent of the volume is introduced to make the model more realistic. This is one of the ten new parameters that are introduced in the atrial model. Six of these parameters are identified with an extension of the previously existing parameter identification method. A method to infer important atrial pressure characteristics from the ventricular pressure waveform is also developed. Identification of the model parameters with and without atria are performed using data sets from a pulmonary embolism pig trial. The error is bigger in the model containing the atria, but remains of the order of measurement errors. The model with atria provides useful information about these two new compartments, without requiring the need for new measurements. This work is a useful improvement of the already existing model and identification methods as it now allows characterization of atrial function.

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  • Analytical Investigation of the Effects of HF2V Damping Devices on the Seismic Performance of the SAC3 Building

    Rodgers, G.W.; Chase, J.G.; MacRae, G.; Bacht, T.; Desombre, J.J.; Dhakal, R.P. (2009)

    Conference Contributions - Published
    University of Canterbury Library

    In this paper, the seismic performance of the 3 storey seismic frame with rigid moment connections at the beam ends (commonly known as the SAC3 building) is compared with that of the same frame using semi-rigid connections with high force to volume (HF2V) lead dissipators. The presence of the gravity frames in the model is also considered. It was found that the placement of dissipators, ignoring the effect of the gravity frames, caused a 12% increase in period of the frame due to the decreased stiffness of the connections. During design level ground shaking the semi-rigid connections with HF2V dissipators have slightly lower accelerations, up to an 80% increase in peak drift, and a 200% increase in the permanent displacement compared to the as-designed case, but no structural damage is expected. When the gravity frames are considered, the floor accelerations decrease further, the peak displacements do not significantly change, but the residual storey dirft ratios reduce to approximately 0.17%. This result is less than one half that of the as-designed frame, where typically gravity frame effects are not considered. The analyses show that combining HF2V lead dissipators with gravity frames and well-designed non-structural elements creates a system with almost no structural damage and low residual displacements.

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  • Using Upper Storeys as Semi-Active Tuned Mass Damper Building Systems - A Case Study Analysis

    Chey, M-H.; Rodgers, G.W.; Chase, J.G.; Mander, J.B. (2010)

    Journal Articles
    University of Canterbury Library

    This paper presents an exploratory case study based analysis of the seismic performance of multistorey passive and semi-active tuned mass damper (PTMD and SATMD) building systems are investigated for 12-storey moment resisting frames modelled as ‘10+2’ storey and ‘8+4’ storey. Segmented upper stories of the structure are isolated as a tuned mass, and a passive viscous damper or semi-active resetable device is adopted for energy dissipation. Optimum TMD control parameters and appropriate matching SATMD configurations are adopted from a companion study on a simplified two degree of freedom (2-DOF) system. Log-normal statistical performance results are presented for 30 probabilistically scaled earthquake records. The time history analysis and normalised reduction factor results show the response reductions for all seismic hazards. Thus, large SATMD systems can effectively manage seismic response for multi degree of freedom (MDOF) systems across a broad range of ground motions in comparison to passive solutions. This research demonstrates the validity of the TMD building systems for consideration in future design and construction. It also provides a template for the design and analysis of passive or semi-active TMD buildings utilising large masses, or more efficiently, added storys, for improving seismic response performance.

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