Don Hettiarachchi - Academia.edu (original) (raw)

Papers by Don Hettiarachchi

Photonics

This study introduces electro-optical (EO) sensors (TurbNet sensors) that utilize a remote laser ... more This study introduces electro-optical (EO) sensors (TurbNet sensors) that utilize a remote laser beacon (either coherent or incoherent) and an optical receiver with CCD camera and embedded edge AI computer (Jetson Xavier Nx) for in situ evaluation of the path-averaged atmospheric turbulence refractive index structure parameter Cn2 at a high temporal rate. Evaluation of Cn2 values was performed using deep neural network (DNN)-based real-time processing of short-exposure laser-beacon light intensity scintillation patterns (images) captured by a TurbNet sensor optical receiver. Several pre-trained DNN models were loaded onto the AI computer and used for TurbNet sensor performance evaluation in a set of atmospheric propagation inference trials under diverse turbulence and meteorological conditions. DNN model training, validation, and testing were performed using datasets comprised of a large number of instances of scintillation frames and corresponding reference (“true”) Cn2 values that...

Real-Time Image Processing and Deep Learning 2022, May 27, 2022

Conventionally, the Fast Fourier Transform (FFT) has been adopted over the Discrete Fourier Trans... more Conventionally, the Fast Fourier Transform (FFT) has been adopted over the Discrete Fourier Transform (DFT) due to its faster execution. However, the emergence of modern high performance computing devices has favored the DFT algorithm due to its inherent parallelism. This letter explores a straightforward one-dimensional DFT whose performance is evaluated against the NVIDIA and AMD’s highly optimized FFT libraries, cuFFT and clFFT, respectively. Performance is analyzed in terms of average kernel execution time for data ranging from 21 to 225 samples across the NVIDIA GeForce GTX 1080 Ti and AMD Radeon RX 6800 XT graphical processors. The DFT algorithm achieves comparable results to the FFT routines for smaller input sizes whereas it significantly outperforms the FFT libraries for larger input lengths. The DFT shows an average performance increase of 177.7% over the cuFFT on the NVIDIA GeForce device using the CUDA toolkit. For the AMD Radeon graphical processor, the DFT outperforms ...

Free-Space Laser Communications XXXIV, 2022

Drilling is one of the most important processes in hard rock mining. With the rapid fluctuations ... more Drilling is one of the most important processes in hard rock mining. With the rapid fluctuations of the commodity prices, it is vital to gain the maximum recovery with the minimum extraction cost at all the time. Due to the heavy influence of hard rock drilling towards the extraction of minerals, even a slight increase in productivity in hard rock drilling can lead to a substantial increase in profits for the company. Hence, the recognition of the optimum drilling conditions will assist to minimise the extraction costs as well as to increase the productivity, which will eventually aid to increase the profits of the company. Since tapered button bits can be used in wide range of rock types, they are predominantly adopted in production drilling in mining industry. It is vital to detect the precise moment of button failure of a drill bit during a real time drilling process because a failure of a button can significantly increase the potential to destroy all other buttons and drop the p...

2018 Asia-Pacific Signal and Information Processing Association Annual Summit and Conference (APSIPA ASC)

Frequency-domain algorithms are used frequently to form Synthetic Aperture Radar (SAR) images fro... more Frequency-domain algorithms are used frequently to form Synthetic Aperture Radar (SAR) images from SAR video phase histories (VPH). Even though frequency-domain algorithms are computationally efficient, they work under many assumptions that do not hold for all imaging cases. Time-domain back projection (BP) algorithms can avoid such problems. The drawback of BP is that it requires a higher number of operations leading to a higher computational complexity in the order of N 3. Recently, various acceleration methods for time domain back projection have been developed in the radar processing community. This paper presents a new acceleration method for SAR BP using fixed-point arithmetic. It is shown that fixedpoint based BP algorithm is faster than traditional algorithm and it maintains a high output image quality. The proposed algorithm process images with 15.69% speedup on average, while maintaining high quality image outputs.

2020 10th Annual Computing and Communication Workshop and Conference (CCWC)

Historically, FPGA designers have used integer processing whenever possible because floating-poin... more Historically, FPGA designers have used integer processing whenever possible because floating-point processing was prohibitively costly due to higher logic requirements and speed reduction. Therefore, fixed-point processing was the norm. Recently, Intel introduced the Arria 10 FPGA which is the industry's first FPGA that includes single-precision hardened Floating-Point Units (FPUs) on DSP blocks. With the advent of hardened floating-point, FPGA designers have largely abandoned fixed-point processing. This paper introduces a series of arithmetic tests to evaluate whether fixed-point processing is obsolete considering the FPGA performance. A performance metric is developed to calculate the FPGA performance in terms of logic utilization and kernel speed. All programs are tested with Intel Stratix V FPGA which does not have hardened FPUs and Intel Arria 10 FPGA for comparison. The performance metric indicates that, on average, there is a 20.18% performance increase when Stratix V processes fixed-point operations and 27.17% performance increase when Arria 10 processes fixed-point operations. Even with hardened FPUs, it is shown that the Arria 10 FPGA exhibits a significant logic reduction when processing fixed-point operations. The results clearly indicate that the FPGAs perform better when processing converted fixed-point arithmetic operations compared to floating-point arithmetic regardless of whether they include hardened FPUs.

Electronic Imaging

Fast track article for IS&T International Symposium on Electronic Imaging 2020: Intelligent Robot... more Fast track article for IS&T International Symposium on Electronic Imaging 2020: Intelligent Robotics and Industrial Applications using Computer Vision proceedings.

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing

Time-domain back projection (BP) is a widely known method used in Synthetic Aperture Radar (SAR) ... more Time-domain back projection (BP) is a widely known method used in Synthetic Aperture Radar (SAR) image formation. Despite its advantages over other image formation algorithms, the BP method is hindered due to its computational complexity and its requirement of higher number of operations and processing power. Recently, Field Programmable Gate Array (FPGA) devices have been used for BP acceleration mainly due to their parallel processing capabilities, reconfigurability, scalability, and low power requirement. This paper presents a new Fixed-point based BP (FxBP) design for FPGA devices and a Floating-point based BP (FlBP) design to compare performance. Both designs are developed with N-Dimensional Range (NDR) structure and Single Work Item (SWI) structure using OpenCL. The FPGA performance is evaluated using a FPGA performance metric (FPM). It is shown that FxBP-NDR and FxBP-SWI designs generate high quality back projected images compared to FlBP designs, while saving 16.87% and 42.54% on logic resources and gaining 17.90% and 91.62% on FPGA performance in NDR and SWI, respectively. Obtained results clearly indicate that FPGA devices perform significantly better with FxBP designs compared to FlBP designs, even with hardened FPUs.

Energy, Sep 1, 2007

A cost-effective optimum design criterion for Organic Rankine power cycles utilizing low-temperat... more A cost-effective optimum design criterion for Organic Rankine power cycles utilizing low-temperature geothermal heat sources is presented. The ratio of the total heat exchanger area to net power output is used as the objective function and was optimized using the steepest descent method. Evaporation and condensation temperatures, geothermal and cooling water velocities are varied in the optimization method. The optimum cycle performance is evaluated and compared for working fluids that include ammonia, HCFC123, n-Pentane and PF5050. The optimization method converges to a unique solution for specific values of evaporation and condensation temperatures and geothermal and cooling water velocities. The choice of working fluid can be greatly affect the objective function which is a measure of power plant cost and in some instances the difference could be more than twice. Ammonia has minimum objective function and maximum geothermal water utilization, but not necessarily maximum cycle efficiency. Exergy analysis shows that efficiency of the ammonia cycle has been largely compromised in the optimization process than that of other working fluids. The fluids, HCFC 123 and n-Pentane, have better performance than PF 5050, although the latter has most preferable physical and chemical characteristics compared to other fluids considered.

In this paper we evaluate the potential benefits from separating process air stream at the exit o... more In this paper we evaluate the potential benefits from separating process air stream at the exit of rotary dehumidifier into two streams. One air stream, hot and humid, is called purge air stream and other is remaining process air stream. The remaining process air stream has a lower temperature and humidity ratio as result of separation of initial hot process air stream. It is found that as the purge angle increases the exit humidity ratio of remaining process air stream decreases up to a point where it reaches a minimum. The purge angle for which this occurs is named "effective purge angle". The effective purge angles for different splits between adsorption and desorption side of the rotary dehumidifier, various regeneration temperatures, non-dimensional lengths and their corresponding optimum non-dimensional times are determined. An existing finite-difference model, developed by the authors of this paper, for simulation of desiccant wheel performance is extended to account for the separation of the process air stream at the exit of rotary dehumidifier and later mixing of purge air stream and outside air to form the regeneration air stream. The performance of desiccant wheel with heated "effective purge angle" is evaluated and compared with performance of the same wheel without purge angle at all. It is found, for all cases considered in this study, that having heated "effective purge angle" has overall positive effect on the performance of the rotary dehumidifier.

Nano Fluids and Critical Heat Flux. [ASME Conference Proceedings 2008, 623 (2008)]. Mihajlo Golub... more Nano Fluids and Critical Heat Flux. [ASME Conference Proceedings 2008, 623 (2008)]. Mihajlo Golubovic, HD Madhawa Hettiarachchi, William M. Worek. Abstract. In recent years nanofluids have been attracting significant attention in the heat transfer research community. ...

Computer Aided Chemical Engineering

Intrathecal drug delivery bypasses the blood brain barrier by infusing therapeutic agents into th... more Intrathecal drug delivery bypasses the blood brain barrier by infusing therapeutic agents into the cerebrospinal fluid. Clinical studies have observed rapid distribution of intrathecally infused drugs. We hypothesize that naturally occurring cerebrospinal fluid pulsations inside the spinal canal accelerate drug transport. An experimental model of the human spinal canal was built for infusion tests of a radionucleotide in stagnant and pulsatile flow fields. The distribution of infused Technitium-99m in the spinal canal model was quantified and validated with computational study. The results show that the oscillatory flow of the cerebrospinal fluid accelerates species dispersion in the spinal canal model by a factor of two to four. To demonstrate a clinically relevant application, physiological cerebrospinal fluid pulsations were reproduced in an anatomically consistent computational model and the dispersion of baclofen, an anti-spasticity drug, inside the central nervous system was p...

The effect of the longitudinal heat conduction in the exchanger wall of a compact-plate cross flo... more The effect of the longitudinal heat conduction in the exchanger wall of a compact-plate cross flow indirect evaporative cooler is investigated. A NTU method is used to study the heat and mass transfer characteristics. A block iterative numerical method is used to solve the coupled conservation equations for the primary fluid, the secondary fluid and the liquid film. The model was validated using previously published data. The exchanger performance deterioration due to the conduction effect has been determined for various design and operating conditions. The results indicate that the thermal performance deterioration of the evaporative coolers may become significant for some typical operating conditions and could be as high as 10%, while it lies less than 5% for most conservative conditions.

Anesthesia & Analgesia, 2012

Intrathecal drug delivery is an efficient method to administer therapeutic molecules to the centr... more Intrathecal drug delivery is an efficient method to administer therapeutic molecules to the central nervous system. However, even with identical drug dosage and administration mode, the extent of drug distribution in vivo is highly variable and difficult to control. Different cerebrospinal fluid (CSF) pulsatility from patient to patient may lead to different drug distribution. Medical image-based computational fluid dynamics (miCFD) is used to construct a patient-specific model to quantify drug transport as a function of a spectrum of physiological CSF pulsations. Magnetic resonance imaging (MRI) and CINE MRI were performed to capture the patient's central nervous system anatomy and CSF pulsatile flow velocities. An miCFD model was reconstructed from these MRIs and the patient's CSF flow velocities were computed. The effect of CSF pulsatility (frequency and stroke volume) was investigated for a bolus injection of a model drug at the L2 vertebral level. Drug distribution profiles along the entire spine were computed for different heart rates: 43, 60, and 120 bpm, and varied CSF stroke volumes: 1, 2, and 3 mL. To assess toxicity risk for patients with different physiological variables, therapeutic and toxic concentration thresholds for a common anesthetic were derived from experimental studies. Toxicity risk analysis was performed for an injection of a spinal anesthetic for patients with different heart rates and CSF stroke volumes. Both heart rate and CSF stroke volume of the patient strongly influence drug distribution administered intrathecally. Doubling the heart rate (from 60 to 120 bpm) caused a 26.4% decrease in peak concentration in CSF after injection. Doubling the CSF stroke volume diminished the peak concentration after injection by 38.1%. Computations show that potentially toxic peak concentrations due to injection can be avoided by changing the infusion rate. Using slower infusion rates could avoid high peak concentrations in CSF while maintaining drug concentrations above the therapeutic threshold. Our computations identify key variables for patient to patient variability in drug distribution in the spine observed clinically. The speed of drug transport is strongly affected by the frequency and magnitude of CSF pulsations. Toxicity risks associated with an injection can be reduced for a particular patient by adjusting the infusion variables with our rigorous miCFD model.

… communications in heat …, 2006

ABSTRACT The Lewis relation is an important part of the equations that govern simultaneous heat a... more ABSTRACT The Lewis relation is an important part of the equations that govern simultaneous heat and mass transfer processes that take place in many engineering devices. Usually, the assumption is made that the value of Lewis relation is equal to 1 which is not always realistic. As result, a new method is presented for evaluation of Lewis relation. This method is then used to evaluate Lewis relation in the case of the flow of free air stream over a flat planar test specimen. The flat planar materials used to demonstrate the method in this work is made out of two different materials, bleached paper and bleached paper/Na-silicate.

Photonics

This study introduces electro-optical (EO) sensors (TurbNet sensors) that utilize a remote laser ... more This study introduces electro-optical (EO) sensors (TurbNet sensors) that utilize a remote laser beacon (either coherent or incoherent) and an optical receiver with CCD camera and embedded edge AI computer (Jetson Xavier Nx) for in situ evaluation of the path-averaged atmospheric turbulence refractive index structure parameter Cn2 at a high temporal rate. Evaluation of Cn2 values was performed using deep neural network (DNN)-based real-time processing of short-exposure laser-beacon light intensity scintillation patterns (images) captured by a TurbNet sensor optical receiver. Several pre-trained DNN models were loaded onto the AI computer and used for TurbNet sensor performance evaluation in a set of atmospheric propagation inference trials under diverse turbulence and meteorological conditions. DNN model training, validation, and testing were performed using datasets comprised of a large number of instances of scintillation frames and corresponding reference (“true”) Cn2 values that...

Real-Time Image Processing and Deep Learning 2022, May 27, 2022

Conventionally, the Fast Fourier Transform (FFT) has been adopted over the Discrete Fourier Trans... more Conventionally, the Fast Fourier Transform (FFT) has been adopted over the Discrete Fourier Transform (DFT) due to its faster execution. However, the emergence of modern high performance computing devices has favored the DFT algorithm due to its inherent parallelism. This letter explores a straightforward one-dimensional DFT whose performance is evaluated against the NVIDIA and AMD’s highly optimized FFT libraries, cuFFT and clFFT, respectively. Performance is analyzed in terms of average kernel execution time for data ranging from 21 to 225 samples across the NVIDIA GeForce GTX 1080 Ti and AMD Radeon RX 6800 XT graphical processors. The DFT algorithm achieves comparable results to the FFT routines for smaller input sizes whereas it significantly outperforms the FFT libraries for larger input lengths. The DFT shows an average performance increase of 177.7% over the cuFFT on the NVIDIA GeForce device using the CUDA toolkit. For the AMD Radeon graphical processor, the DFT outperforms ...

Free-Space Laser Communications XXXIV, 2022

Drilling is one of the most important processes in hard rock mining. With the rapid fluctuations ... more Drilling is one of the most important processes in hard rock mining. With the rapid fluctuations of the commodity prices, it is vital to gain the maximum recovery with the minimum extraction cost at all the time. Due to the heavy influence of hard rock drilling towards the extraction of minerals, even a slight increase in productivity in hard rock drilling can lead to a substantial increase in profits for the company. Hence, the recognition of the optimum drilling conditions will assist to minimise the extraction costs as well as to increase the productivity, which will eventually aid to increase the profits of the company. Since tapered button bits can be used in wide range of rock types, they are predominantly adopted in production drilling in mining industry. It is vital to detect the precise moment of button failure of a drill bit during a real time drilling process because a failure of a button can significantly increase the potential to destroy all other buttons and drop the p...

2018 Asia-Pacific Signal and Information Processing Association Annual Summit and Conference (APSIPA ASC)

Frequency-domain algorithms are used frequently to form Synthetic Aperture Radar (SAR) images fro... more Frequency-domain algorithms are used frequently to form Synthetic Aperture Radar (SAR) images from SAR video phase histories (VPH). Even though frequency-domain algorithms are computationally efficient, they work under many assumptions that do not hold for all imaging cases. Time-domain back projection (BP) algorithms can avoid such problems. The drawback of BP is that it requires a higher number of operations leading to a higher computational complexity in the order of N 3. Recently, various acceleration methods for time domain back projection have been developed in the radar processing community. This paper presents a new acceleration method for SAR BP using fixed-point arithmetic. It is shown that fixedpoint based BP algorithm is faster than traditional algorithm and it maintains a high output image quality. The proposed algorithm process images with 15.69% speedup on average, while maintaining high quality image outputs.

2020 10th Annual Computing and Communication Workshop and Conference (CCWC)

Historically, FPGA designers have used integer processing whenever possible because floating-poin... more Historically, FPGA designers have used integer processing whenever possible because floating-point processing was prohibitively costly due to higher logic requirements and speed reduction. Therefore, fixed-point processing was the norm. Recently, Intel introduced the Arria 10 FPGA which is the industry's first FPGA that includes single-precision hardened Floating-Point Units (FPUs) on DSP blocks. With the advent of hardened floating-point, FPGA designers have largely abandoned fixed-point processing. This paper introduces a series of arithmetic tests to evaluate whether fixed-point processing is obsolete considering the FPGA performance. A performance metric is developed to calculate the FPGA performance in terms of logic utilization and kernel speed. All programs are tested with Intel Stratix V FPGA which does not have hardened FPUs and Intel Arria 10 FPGA for comparison. The performance metric indicates that, on average, there is a 20.18% performance increase when Stratix V processes fixed-point operations and 27.17% performance increase when Arria 10 processes fixed-point operations. Even with hardened FPUs, it is shown that the Arria 10 FPGA exhibits a significant logic reduction when processing fixed-point operations. The results clearly indicate that the FPGAs perform better when processing converted fixed-point arithmetic operations compared to floating-point arithmetic regardless of whether they include hardened FPUs.

Electronic Imaging

Fast track article for IS&T International Symposium on Electronic Imaging 2020: Intelligent Robot... more Fast track article for IS&T International Symposium on Electronic Imaging 2020: Intelligent Robotics and Industrial Applications using Computer Vision proceedings.

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing

Time-domain back projection (BP) is a widely known method used in Synthetic Aperture Radar (SAR) ... more Time-domain back projection (BP) is a widely known method used in Synthetic Aperture Radar (SAR) image formation. Despite its advantages over other image formation algorithms, the BP method is hindered due to its computational complexity and its requirement of higher number of operations and processing power. Recently, Field Programmable Gate Array (FPGA) devices have been used for BP acceleration mainly due to their parallel processing capabilities, reconfigurability, scalability, and low power requirement. This paper presents a new Fixed-point based BP (FxBP) design for FPGA devices and a Floating-point based BP (FlBP) design to compare performance. Both designs are developed with N-Dimensional Range (NDR) structure and Single Work Item (SWI) structure using OpenCL. The FPGA performance is evaluated using a FPGA performance metric (FPM). It is shown that FxBP-NDR and FxBP-SWI designs generate high quality back projected images compared to FlBP designs, while saving 16.87% and 42.54% on logic resources and gaining 17.90% and 91.62% on FPGA performance in NDR and SWI, respectively. Obtained results clearly indicate that FPGA devices perform significantly better with FxBP designs compared to FlBP designs, even with hardened FPUs.

Energy, Sep 1, 2007

A cost-effective optimum design criterion for Organic Rankine power cycles utilizing low-temperat... more A cost-effective optimum design criterion for Organic Rankine power cycles utilizing low-temperature geothermal heat sources is presented. The ratio of the total heat exchanger area to net power output is used as the objective function and was optimized using the steepest descent method. Evaporation and condensation temperatures, geothermal and cooling water velocities are varied in the optimization method. The optimum cycle performance is evaluated and compared for working fluids that include ammonia, HCFC123, n-Pentane and PF5050. The optimization method converges to a unique solution for specific values of evaporation and condensation temperatures and geothermal and cooling water velocities. The choice of working fluid can be greatly affect the objective function which is a measure of power plant cost and in some instances the difference could be more than twice. Ammonia has minimum objective function and maximum geothermal water utilization, but not necessarily maximum cycle efficiency. Exergy analysis shows that efficiency of the ammonia cycle has been largely compromised in the optimization process than that of other working fluids. The fluids, HCFC 123 and n-Pentane, have better performance than PF 5050, although the latter has most preferable physical and chemical characteristics compared to other fluids considered.

In this paper we evaluate the potential benefits from separating process air stream at the exit o... more In this paper we evaluate the potential benefits from separating process air stream at the exit of rotary dehumidifier into two streams. One air stream, hot and humid, is called purge air stream and other is remaining process air stream. The remaining process air stream has a lower temperature and humidity ratio as result of separation of initial hot process air stream. It is found that as the purge angle increases the exit humidity ratio of remaining process air stream decreases up to a point where it reaches a minimum. The purge angle for which this occurs is named "effective purge angle". The effective purge angles for different splits between adsorption and desorption side of the rotary dehumidifier, various regeneration temperatures, non-dimensional lengths and their corresponding optimum non-dimensional times are determined. An existing finite-difference model, developed by the authors of this paper, for simulation of desiccant wheel performance is extended to account for the separation of the process air stream at the exit of rotary dehumidifier and later mixing of purge air stream and outside air to form the regeneration air stream. The performance of desiccant wheel with heated "effective purge angle" is evaluated and compared with performance of the same wheel without purge angle at all. It is found, for all cases considered in this study, that having heated "effective purge angle" has overall positive effect on the performance of the rotary dehumidifier.

Nano Fluids and Critical Heat Flux. [ASME Conference Proceedings 2008, 623 (2008)]. Mihajlo Golub... more Nano Fluids and Critical Heat Flux. [ASME Conference Proceedings 2008, 623 (2008)]. Mihajlo Golubovic, HD Madhawa Hettiarachchi, William M. Worek. Abstract. In recent years nanofluids have been attracting significant attention in the heat transfer research community. ...

Computer Aided Chemical Engineering

Intrathecal drug delivery bypasses the blood brain barrier by infusing therapeutic agents into th... more Intrathecal drug delivery bypasses the blood brain barrier by infusing therapeutic agents into the cerebrospinal fluid. Clinical studies have observed rapid distribution of intrathecally infused drugs. We hypothesize that naturally occurring cerebrospinal fluid pulsations inside the spinal canal accelerate drug transport. An experimental model of the human spinal canal was built for infusion tests of a radionucleotide in stagnant and pulsatile flow fields. The distribution of infused Technitium-99m in the spinal canal model was quantified and validated with computational study. The results show that the oscillatory flow of the cerebrospinal fluid accelerates species dispersion in the spinal canal model by a factor of two to four. To demonstrate a clinically relevant application, physiological cerebrospinal fluid pulsations were reproduced in an anatomically consistent computational model and the dispersion of baclofen, an anti-spasticity drug, inside the central nervous system was p...

The effect of the longitudinal heat conduction in the exchanger wall of a compact-plate cross flo... more The effect of the longitudinal heat conduction in the exchanger wall of a compact-plate cross flow indirect evaporative cooler is investigated. A NTU method is used to study the heat and mass transfer characteristics. A block iterative numerical method is used to solve the coupled conservation equations for the primary fluid, the secondary fluid and the liquid film. The model was validated using previously published data. The exchanger performance deterioration due to the conduction effect has been determined for various design and operating conditions. The results indicate that the thermal performance deterioration of the evaporative coolers may become significant for some typical operating conditions and could be as high as 10%, while it lies less than 5% for most conservative conditions.

Anesthesia & Analgesia, 2012

Intrathecal drug delivery is an efficient method to administer therapeutic molecules to the centr... more Intrathecal drug delivery is an efficient method to administer therapeutic molecules to the central nervous system. However, even with identical drug dosage and administration mode, the extent of drug distribution in vivo is highly variable and difficult to control. Different cerebrospinal fluid (CSF) pulsatility from patient to patient may lead to different drug distribution. Medical image-based computational fluid dynamics (miCFD) is used to construct a patient-specific model to quantify drug transport as a function of a spectrum of physiological CSF pulsations. Magnetic resonance imaging (MRI) and CINE MRI were performed to capture the patient's central nervous system anatomy and CSF pulsatile flow velocities. An miCFD model was reconstructed from these MRIs and the patient's CSF flow velocities were computed. The effect of CSF pulsatility (frequency and stroke volume) was investigated for a bolus injection of a model drug at the L2 vertebral level. Drug distribution profiles along the entire spine were computed for different heart rates: 43, 60, and 120 bpm, and varied CSF stroke volumes: 1, 2, and 3 mL. To assess toxicity risk for patients with different physiological variables, therapeutic and toxic concentration thresholds for a common anesthetic were derived from experimental studies. Toxicity risk analysis was performed for an injection of a spinal anesthetic for patients with different heart rates and CSF stroke volumes. Both heart rate and CSF stroke volume of the patient strongly influence drug distribution administered intrathecally. Doubling the heart rate (from 60 to 120 bpm) caused a 26.4% decrease in peak concentration in CSF after injection. Doubling the CSF stroke volume diminished the peak concentration after injection by 38.1%. Computations show that potentially toxic peak concentrations due to injection can be avoided by changing the infusion rate. Using slower infusion rates could avoid high peak concentrations in CSF while maintaining drug concentrations above the therapeutic threshold. Our computations identify key variables for patient to patient variability in drug distribution in the spine observed clinically. The speed of drug transport is strongly affected by the frequency and magnitude of CSF pulsations. Toxicity risks associated with an injection can be reduced for a particular patient by adjusting the infusion variables with our rigorous miCFD model.

… communications in heat …, 2006

ABSTRACT The Lewis relation is an important part of the equations that govern simultaneous heat a... more ABSTRACT The Lewis relation is an important part of the equations that govern simultaneous heat and mass transfer processes that take place in many engineering devices. Usually, the assumption is made that the value of Lewis relation is equal to 1 which is not always realistic. As result, a new method is presented for evaluation of Lewis relation. This method is then used to evaluate Lewis relation in the case of the flow of free air stream over a flat planar test specimen. The flat planar materials used to demonstrate the method in this work is made out of two different materials, bleached paper and bleached paper/Na-silicate.