The authors place the invasive species problem in context prior to providing species descriptions... more The authors place the invasive species problem in context prior to providing species descriptions. The first three chapters offer background information on how invasive species become established, their impacts, and an overview of approaches to controlling problem species. The fourth chapter consists of a general key for identifying and locating unknown plant species. The majority of the field guide consists of profiles of individual species, including information on taxonomy, identifying characteristics, habitat, geographical range, ecological effects, introduction pathway, management strategies, and additional references. Most species are accompanied by at least two color photos, including a full view and a closeup, that illustrate identifying characteristics. The volume presents unique information not found in other books on invasive species, which tend to be either general case studies of a few species or technical monographs. The portions on ecosystem effects and management str...
Shock tubes have been extensively used in the study of blast traumatic brain injury due to increa... more Shock tubes have been extensively used in the study of blast traumatic brain injury due to increased incidence of blast-induced neurotrauma in Iraq and Afghanistan conflicts. One of the important aspects in these studies is how to best replicate the field conditions in the laboratory which relies on reproducing blast wave profiles. Evolution of the blast wave profiles along the length of the compression-driven air shock tube is studied using experiments and numerical simulations with emphasis on the shape and magnitude of pressure time profiles. In order to measure dynamic pressures of the blast, a series of sensors are mounted on a cylindrical specimen normal to the flow direction. Our results indicate that the blast wave loading is significantly different for locations inside and outside of the shock tube. Pressure profiles inside the shock tube follow the Friedlander waveform fairly well. Upon approaching exit of the shock tube, an expansion wave released from the shock tube edges significantly degrades the pressure profiles. For tests outside the shock tube, peak pressure and total impulse reduce drastically as we move away from the exit and majority of loading is in the form of subsonic jet wind. In addition, the planarity of the blast wave degrades as blast wave evolves three dimensionally. Numerical results visually and quantitatively confirm the presence of vortices, jet wind and three-dimensional expansion of the planar blast wave near the exit. Pressure profiles at 90 • orientation show flow separation. When cylinder is placed inside, this flow separation is not sustained, but when placed outside the shock tube this flow separation Communicated by M. Brouillette.
Computer Methods in Biomechanics and Biomedical Engineering, 2012
The effectiveness of helmets in extenuating the primary shock waves generated by the explosions o... more The effectiveness of helmets in extenuating the primary shock waves generated by the explosions of improvised explosive devices is not clearly understood. In this work, the role of helmet on the overpressurisation and impulse experienced by the head were examined. The shock wave-head interactions were studied under three different cases: (i) unprotected head, (ii) head with helmet but with varying head-helmet gaps and (iii) head covered with helmet and tightly fitting foam pads. The intensification effect was discussed by examining the shock wave flow pattern and verified with experiments. A helmet with a better protection against shock wave is suggested.
Your article is protected by copyright and all rights are held exclusively by Springer-Verlag. Th... more Your article is protected by copyright and all rights are held exclusively by Springer-Verlag. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your work, please use the accepted author's version for posting to your own website or your institution's repository. You may further deposit the accepted author's version on a funder's repository at a funder's request, provided it is not made publicly available until 12 months after publication.
Corridors such as roads and trails can facilitate invasions by non-native plant species. The open... more Corridors such as roads and trails can facilitate invasions by non-native plant species. The open, disturbed habitat associated with corridors provides favorable growing conditions for many non-native plant species. Bike trails are a corridor system common to many urban areas that have not been studied for their potential role in plant invasions. We sampled five linear segments of urban forest along bike trails in Lincoln, Nebraska to assess the invasion of woody non-native species relative to corridors and to assess the composition of these urban forests. The most abundant plant species were generally native species, but five non-native species were also present: white mulberry (Morus alba), common buckthorn (Rhamnus cathartica), tree-of-heaven (Ailanthus altissima), honeysuckle (Lonicera spp.) and elm (Ulmus spp.). The distribution of two of the woody species sampled, common buckthorn and honeysuckle, significantly decreased with increasing distance from a source patch of vegetation (P 5 0.031 and 0.030). These linear habitats are being invaded by non-native tree and shrub species, which may change the structure of these urban forest corridors. If nonnative woody plant species become abundant in the future, they may homogenize the plant community and reduce native biodiversity in these areas.
Blast waves generated by improvised explosive devices (IEDs) cause traumatic brain injury (TBI) i... more Blast waves generated by improvised explosive devices (IEDs) cause traumatic brain injury (TBI) in soldiers and civilians. In vivo animal models that use shock tubes are extensively used in laboratories to simulate field conditions, to identify mechanisms of injury, and to develop injury thresholds. In this article, we place rats in different locations along the length of the shock tube (i.e., inside, outside, and near the exit), to examine the role of animal placement location (APL) in the biomechanical load experienced by the animal. We found that the biomechanical load on the brain and internal organs in the thoracic cavity (lungs and heart) varied significantly depending on the APL. When the specimen is positioned outside, organs in the thoracic cavity experience a higher pressure for a longer duration, in contrast to APL inside the shock tube. This in turn will possibly alter the injury type, severity, and lethality. We found that the optimal APL is where the Friedlander waveform is first formed inside the shock tube. Once the optimal APL was determined, the effect of the incident blast intensity on the surface and intracranial pressure was measured and analyzed. Noticeably, surface and intracranial pressure increases linearly with the incident peak overpressures, though surface pressures are significantly higher than the other two. Further, we developed and validated an anatomically accurate finite element model of the rat head. With this model, we determined that the main pathway of pressure transmission to the brain was through the skull and not through the snout; however, the snout plays a secondary role in diffracting the incoming blast wave towards the skull.
The causes of nomadism, migration, and decline in vertebrates are debated issues in the ecologica... more The causes of nomadism, migration, and decline in vertebrates are debated issues in the ecological sciences. Literature suggests nomadism may arise in species that specialize in granivory, nectivory, or the utilization of rodent outbreaks. Migration is thought to arise as a result of the exploitation of certain scarce or variable food resources. Species decline is hypothesized to be the result of many different factors as well; large species, island species and specialists may be more prone to decline. A fresh perspective regarding the causes for species nomadism, migration, and decline is being investigated utilizing the ideas within the Textural Discontinuity Hypothesis. The Textural Discontinuity Hypothesis stems from complex systems analysis and posits that body mass distributions form aggregations within ecological systems, and that those body mass aggregations reflect discontinuous distributions of resources. Additionally scientists have posited that species at the edges of body mass aggregations may be exposed to highly variable resources. Literature indicates nomadic and declining bird species populations occur at the edges of body mass aggregations more frequently than expected. Migratory bird species also may be located at the edges vii The number of body mass aggregations in South African bird species by habitat and ecosystem, including and excluding aquatic species. The number of aggregations was determined by Bayesian Classification And Regression Tree analyses .
We evaluated the acute (up to 24 hours) pathophysiological response to primary blast using a rat ... more We evaluated the acute (up to 24 hours) pathophysiological response to primary blast using a rat model and helium driven shock tube. The shock tube generates animal loadings with controlled pure primary blast parameters over a wide range and field-relevant conditions. We studied the biomechanical loading with a set of pressure gauges mounted on the surface of the nose, in the cranial space and in the thoracic cavity of cadaver rats. Anesthetized rats were exposed to a single blast at precisely controlled five peak overpressures over a wide range (130, 190, 230, 250 and 290 kPa). We observed 0% mortality rates in 130 and 230 kPa groups, and 30%, 24% and 100% mortality rates in 190, 250 and 290 kPa groups, respectively. The body weight loss was statistically significant in 190 and 250 kPa groups 24 hours after exposure. The data analysis showed the magnitude of peak-to-peak amplitude of intracranial pressure (ICP) fluctuations correlates well with mortality rates. The ICP oscillations recorded for 190, 250 and 290 kPa are characterized by higher frequency (10-20 kHz) than in other two groups (7-8 kHz). We noted acute bradycardia and lung hemorrhage in all groups of rats subjected to the blast. We established the onset of both corresponds to 110 kPa peak overpressure. The immunostaining against immunoglobulin G (IgG) of brain sections of rats sacrificed 24-hours post-exposure indicated the diffuse blood-brain barrier breakdown in the brain parenchyma. At high blast intensities (peak overpressure of 190 kPa or more) the IgG uptake by neurons was evident, but there was no evidence of neurodegeneration after 24 hours post-exposure, as indicated by cupric silver staining. We observed that the acute response as well as mortality is a non-linear function of over the peak overpressure and impulse ranges explored in this work.
The wrist/forearm complex is one of the most commonly fractured body regions, yet the impact tole... more The wrist/forearm complex is one of the most commonly fractured body regions, yet the impact tolerance of the wrist is poorly understood. This study sought to quantify the injury tolerance of the adult male forearm-wrist complex under loading simulating axial impact to an outstretched hand. Fifteen isolated cadaveric forearm/wrist specimens were tested. Loading was applied via an instrumented drop tower device designed to impact the palmar surface of the hand with the wrist extended to approximately 90 degrees. Impact severity was modulated by adjusting the boundary condition of the elbow. Elbow reaction force and deformation of the specimen (deflection of the palmar surface of the hand toward the elbow) were measured. Bone-implanted strain gauges were used to detect the time of fracture. Injury risk functions were developed using parametric survival analysis with a cumulative Weibull distribution. Of 14 specimens, 10 exhibited a fracture to the wrist or forearm after test (one specimen was excluded from the analysis). Injury severities varied from nondisplaced fractures of the radius to severely displaced fractures and/or fracture-dislocations of the carpal bones. Of the potential predictors studied, the specimen deflection expressed as a percentage of the initial specimen length produced the injury risk model of best fit (50% risk of fracture at 1.69% deflection; 95% confidence interval, 1.38-2.07% deflection). The value of the elbow reaction force corresponding to a 50% risk of injury was 4.34 kN (3.80-4.97 kN). These results provide information for the prediction of wrist and forearm injury in biomechanical models simulating impacts in the field and provide tolerance information for the development of injury mitigation countermeasures.
ABSTRACT Shock tubes have been extensively used in the study of blast traumatic brain injury due ... more ABSTRACT Shock tubes have been extensively used in the study of blast traumatic brain injury due to increased incidence of blast-induced neurotrauma in Iraq and Afghanistan conflicts. One of the important aspects in these studies is how to best replicate the field conditions in the laboratory which relies on reproducing blast wave profiles. Evolution of the blast wave profiles along the length of the compression-driven air shock tube is studied using experiments and numerical simulations with emphasis on the shape and magnitude of pressure time profiles. In order to measure dynamic pressures of the blast, a series of sensors are mounted on a cylindrical specimen normal to the flow direction. Our results indicate that the blast wave loading is significantly different for locations inside and outside of the shock tube. Pressure profiles inside the shock tube follow the Friedlander waveform fairly well. Upon approaching exit of the shock tube, an expansion wave released from the shock tube edges significantly degrades the pressure profiles. For tests outside the shock tube, peak pressure and total impulse reduce drastically as we move away from the exit and majority of loading is in the form of subsonic jet wind. In addition, the planarity of the blast wave degrades as blast wave evolves three dimensionally. Numerical results visually and quantitatively confirm the presence of vortices, jet wind and three-dimensional expansion of the planar blast wave near the exit. Pressure profiles at 90° orientation show flow separation. When cylinder is placed inside, this flow separation is not sustained, but when placed outside the shock tube this flow separation is sustained which causes tensile loading on the sides of the cylinder. Friedlander waves formed due to field explosives in the intermediate-to far-field ranges are replicated in a narrow test region located deep inside the shock tube.
Blast waves generated by improvised explosive devices (IEDs) cause traumatic brain injury (TBI) i... more Blast waves generated by improvised explosive devices (IEDs) cause traumatic brain injury (TBI) in soldiers and civilians. In vivo animal models that use shock tubes are extensively used in laboratories to simulate field conditions, to identify mechanisms of injury, and to develop injury thresholds. In this article, we place rats in different locations along the length of the shock tube (i.e., inside, outside, and near the exit), to examine the role of animal placement location (APL) in the biomechanical load experienced by the animal. We found that the biomechanical load on the brain and internal organs in the thoracic cavity (lungs and heart) varied significantly depending on the APL. When the specimen is positioned outside, organs in the thoracic cavity experience a higher pressure for a longer duration, in contrast to APL inside the shock tube. This in turn will possibly alter the injury type, severity, and lethality. We found that the optimal APL is where the Friedlander waveform is first formed inside the shock tube. Once the optimal APL was determined, the effect of the incident blast intensity on the surface and intracranial pressure was measured and analyzed. Noticeably, surface and intracranial pressure increases linearly with the incident peak overpressures, though surface pressures are significantly higher than the other two. Further, we developed and validated an anatomically accurate finite element model of the rat head. With this model, we determined that the main pathway of pressure transmission to the brain was through the skull and not through the snout; however, the snout plays a secondary role in diffracting the incoming blast wave towards the skull.
Computer Methods in Biomechanics and Biomedical Engineering, 2012
The effectiveness of helmets in extenuating the primary shock waves generated by the explosions o... more The effectiveness of helmets in extenuating the primary shock waves generated by the explosions of improvised explosive devices is not clearly understood. In this work, the role of helmet on the overpressurization and impulse experienced by the head were examined. The shock wave-head interactions were studied under three different cases: (i) unprotected head, (ii) head with helmet but with varying head-helmet gaps and (iii) head covered with helmet and tightly fitting foam pads. The intensification effect was discussed by examining the shock wave flow pattern and verified with experiments. A helmet with a better protection against shock wave is suggested.
Blast waves generated by improvised explosive devices can cause mild, moderate to severe traumati... more Blast waves generated by improvised explosive devices can cause mild, moderate to severe traumatic brain injury in soldiers and civilians. To understand the interactions of blast waves on the head and brain and to identify the mechanisms of injury, compression-driven air shock tubes are extensively used in laboratory settings to simulate the field conditions. The overall goal of this effort is to understand the mechanics of blast wave-head interactions as the blast wave traverses the head/brain continuum. Toward this goal, surrogate head model is subjected to well-controlled blast wave profile in the shock tube environment, and the results are analyzed using combined experimental and numerical approaches. The validated numerical models are then used to investigate the spatiotemporal distribution of stresses and pressure in the human skull and brain. By detailing the results from a series of careful experiments and numerical simulations, this paper demonstrates that: (1) Geometry of the head governs the flow dynamics around the head which in turn determines the net mechanical load on the head. (2) Biomechanical loading of the brain is governed by direct wave transmission, structural deformations, and wave reflections from tissue-material interfaces. (3) Deformation and stress analysis of the skull and brain show that skull flexure and tissue cavitation are possible mechanisms of blast-induced traumatic brain injury.
The authors place the invasive species problem in context prior to providing species descriptions... more The authors place the invasive species problem in context prior to providing species descriptions. The first three chapters offer background information on how invasive species become established, their impacts, and an overview of approaches to controlling problem species. The fourth chapter consists of a general key for identifying and locating unknown plant species. The majority of the field guide consists of profiles of individual species, including information on taxonomy, identifying characteristics, habitat, geographical range, ecological effects, introduction pathway, management strategies, and additional references. Most species are accompanied by at least two color photos, including a full view and a closeup, that illustrate identifying characteristics. The volume presents unique information not found in other books on invasive species, which tend to be either general case studies of a few species or technical monographs. The portions on ecosystem effects and management str...
Shock tubes have been extensively used in the study of blast traumatic brain injury due to increa... more Shock tubes have been extensively used in the study of blast traumatic brain injury due to increased incidence of blast-induced neurotrauma in Iraq and Afghanistan conflicts. One of the important aspects in these studies is how to best replicate the field conditions in the laboratory which relies on reproducing blast wave profiles. Evolution of the blast wave profiles along the length of the compression-driven air shock tube is studied using experiments and numerical simulations with emphasis on the shape and magnitude of pressure time profiles. In order to measure dynamic pressures of the blast, a series of sensors are mounted on a cylindrical specimen normal to the flow direction. Our results indicate that the blast wave loading is significantly different for locations inside and outside of the shock tube. Pressure profiles inside the shock tube follow the Friedlander waveform fairly well. Upon approaching exit of the shock tube, an expansion wave released from the shock tube edges significantly degrades the pressure profiles. For tests outside the shock tube, peak pressure and total impulse reduce drastically as we move away from the exit and majority of loading is in the form of subsonic jet wind. In addition, the planarity of the blast wave degrades as blast wave evolves three dimensionally. Numerical results visually and quantitatively confirm the presence of vortices, jet wind and three-dimensional expansion of the planar blast wave near the exit. Pressure profiles at 90 • orientation show flow separation. When cylinder is placed inside, this flow separation is not sustained, but when placed outside the shock tube this flow separation Communicated by M. Brouillette.
Computer Methods in Biomechanics and Biomedical Engineering, 2012
The effectiveness of helmets in extenuating the primary shock waves generated by the explosions o... more The effectiveness of helmets in extenuating the primary shock waves generated by the explosions of improvised explosive devices is not clearly understood. In this work, the role of helmet on the overpressurisation and impulse experienced by the head were examined. The shock wave-head interactions were studied under three different cases: (i) unprotected head, (ii) head with helmet but with varying head-helmet gaps and (iii) head covered with helmet and tightly fitting foam pads. The intensification effect was discussed by examining the shock wave flow pattern and verified with experiments. A helmet with a better protection against shock wave is suggested.
Your article is protected by copyright and all rights are held exclusively by Springer-Verlag. Th... more Your article is protected by copyright and all rights are held exclusively by Springer-Verlag. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your work, please use the accepted author's version for posting to your own website or your institution's repository. You may further deposit the accepted author's version on a funder's repository at a funder's request, provided it is not made publicly available until 12 months after publication.
Corridors such as roads and trails can facilitate invasions by non-native plant species. The open... more Corridors such as roads and trails can facilitate invasions by non-native plant species. The open, disturbed habitat associated with corridors provides favorable growing conditions for many non-native plant species. Bike trails are a corridor system common to many urban areas that have not been studied for their potential role in plant invasions. We sampled five linear segments of urban forest along bike trails in Lincoln, Nebraska to assess the invasion of woody non-native species relative to corridors and to assess the composition of these urban forests. The most abundant plant species were generally native species, but five non-native species were also present: white mulberry (Morus alba), common buckthorn (Rhamnus cathartica), tree-of-heaven (Ailanthus altissima), honeysuckle (Lonicera spp.) and elm (Ulmus spp.). The distribution of two of the woody species sampled, common buckthorn and honeysuckle, significantly decreased with increasing distance from a source patch of vegetation (P 5 0.031 and 0.030). These linear habitats are being invaded by non-native tree and shrub species, which may change the structure of these urban forest corridors. If nonnative woody plant species become abundant in the future, they may homogenize the plant community and reduce native biodiversity in these areas.
Blast waves generated by improvised explosive devices (IEDs) cause traumatic brain injury (TBI) i... more Blast waves generated by improvised explosive devices (IEDs) cause traumatic brain injury (TBI) in soldiers and civilians. In vivo animal models that use shock tubes are extensively used in laboratories to simulate field conditions, to identify mechanisms of injury, and to develop injury thresholds. In this article, we place rats in different locations along the length of the shock tube (i.e., inside, outside, and near the exit), to examine the role of animal placement location (APL) in the biomechanical load experienced by the animal. We found that the biomechanical load on the brain and internal organs in the thoracic cavity (lungs and heart) varied significantly depending on the APL. When the specimen is positioned outside, organs in the thoracic cavity experience a higher pressure for a longer duration, in contrast to APL inside the shock tube. This in turn will possibly alter the injury type, severity, and lethality. We found that the optimal APL is where the Friedlander waveform is first formed inside the shock tube. Once the optimal APL was determined, the effect of the incident blast intensity on the surface and intracranial pressure was measured and analyzed. Noticeably, surface and intracranial pressure increases linearly with the incident peak overpressures, though surface pressures are significantly higher than the other two. Further, we developed and validated an anatomically accurate finite element model of the rat head. With this model, we determined that the main pathway of pressure transmission to the brain was through the skull and not through the snout; however, the snout plays a secondary role in diffracting the incoming blast wave towards the skull.
The causes of nomadism, migration, and decline in vertebrates are debated issues in the ecologica... more The causes of nomadism, migration, and decline in vertebrates are debated issues in the ecological sciences. Literature suggests nomadism may arise in species that specialize in granivory, nectivory, or the utilization of rodent outbreaks. Migration is thought to arise as a result of the exploitation of certain scarce or variable food resources. Species decline is hypothesized to be the result of many different factors as well; large species, island species and specialists may be more prone to decline. A fresh perspective regarding the causes for species nomadism, migration, and decline is being investigated utilizing the ideas within the Textural Discontinuity Hypothesis. The Textural Discontinuity Hypothesis stems from complex systems analysis and posits that body mass distributions form aggregations within ecological systems, and that those body mass aggregations reflect discontinuous distributions of resources. Additionally scientists have posited that species at the edges of body mass aggregations may be exposed to highly variable resources. Literature indicates nomadic and declining bird species populations occur at the edges of body mass aggregations more frequently than expected. Migratory bird species also may be located at the edges vii The number of body mass aggregations in South African bird species by habitat and ecosystem, including and excluding aquatic species. The number of aggregations was determined by Bayesian Classification And Regression Tree analyses .
We evaluated the acute (up to 24 hours) pathophysiological response to primary blast using a rat ... more We evaluated the acute (up to 24 hours) pathophysiological response to primary blast using a rat model and helium driven shock tube. The shock tube generates animal loadings with controlled pure primary blast parameters over a wide range and field-relevant conditions. We studied the biomechanical loading with a set of pressure gauges mounted on the surface of the nose, in the cranial space and in the thoracic cavity of cadaver rats. Anesthetized rats were exposed to a single blast at precisely controlled five peak overpressures over a wide range (130, 190, 230, 250 and 290 kPa). We observed 0% mortality rates in 130 and 230 kPa groups, and 30%, 24% and 100% mortality rates in 190, 250 and 290 kPa groups, respectively. The body weight loss was statistically significant in 190 and 250 kPa groups 24 hours after exposure. The data analysis showed the magnitude of peak-to-peak amplitude of intracranial pressure (ICP) fluctuations correlates well with mortality rates. The ICP oscillations recorded for 190, 250 and 290 kPa are characterized by higher frequency (10-20 kHz) than in other two groups (7-8 kHz). We noted acute bradycardia and lung hemorrhage in all groups of rats subjected to the blast. We established the onset of both corresponds to 110 kPa peak overpressure. The immunostaining against immunoglobulin G (IgG) of brain sections of rats sacrificed 24-hours post-exposure indicated the diffuse blood-brain barrier breakdown in the brain parenchyma. At high blast intensities (peak overpressure of 190 kPa or more) the IgG uptake by neurons was evident, but there was no evidence of neurodegeneration after 24 hours post-exposure, as indicated by cupric silver staining. We observed that the acute response as well as mortality is a non-linear function of over the peak overpressure and impulse ranges explored in this work.
The wrist/forearm complex is one of the most commonly fractured body regions, yet the impact tole... more The wrist/forearm complex is one of the most commonly fractured body regions, yet the impact tolerance of the wrist is poorly understood. This study sought to quantify the injury tolerance of the adult male forearm-wrist complex under loading simulating axial impact to an outstretched hand. Fifteen isolated cadaveric forearm/wrist specimens were tested. Loading was applied via an instrumented drop tower device designed to impact the palmar surface of the hand with the wrist extended to approximately 90 degrees. Impact severity was modulated by adjusting the boundary condition of the elbow. Elbow reaction force and deformation of the specimen (deflection of the palmar surface of the hand toward the elbow) were measured. Bone-implanted strain gauges were used to detect the time of fracture. Injury risk functions were developed using parametric survival analysis with a cumulative Weibull distribution. Of 14 specimens, 10 exhibited a fracture to the wrist or forearm after test (one specimen was excluded from the analysis). Injury severities varied from nondisplaced fractures of the radius to severely displaced fractures and/or fracture-dislocations of the carpal bones. Of the potential predictors studied, the specimen deflection expressed as a percentage of the initial specimen length produced the injury risk model of best fit (50% risk of fracture at 1.69% deflection; 95% confidence interval, 1.38-2.07% deflection). The value of the elbow reaction force corresponding to a 50% risk of injury was 4.34 kN (3.80-4.97 kN). These results provide information for the prediction of wrist and forearm injury in biomechanical models simulating impacts in the field and provide tolerance information for the development of injury mitigation countermeasures.
ABSTRACT Shock tubes have been extensively used in the study of blast traumatic brain injury due ... more ABSTRACT Shock tubes have been extensively used in the study of blast traumatic brain injury due to increased incidence of blast-induced neurotrauma in Iraq and Afghanistan conflicts. One of the important aspects in these studies is how to best replicate the field conditions in the laboratory which relies on reproducing blast wave profiles. Evolution of the blast wave profiles along the length of the compression-driven air shock tube is studied using experiments and numerical simulations with emphasis on the shape and magnitude of pressure time profiles. In order to measure dynamic pressures of the blast, a series of sensors are mounted on a cylindrical specimen normal to the flow direction. Our results indicate that the blast wave loading is significantly different for locations inside and outside of the shock tube. Pressure profiles inside the shock tube follow the Friedlander waveform fairly well. Upon approaching exit of the shock tube, an expansion wave released from the shock tube edges significantly degrades the pressure profiles. For tests outside the shock tube, peak pressure and total impulse reduce drastically as we move away from the exit and majority of loading is in the form of subsonic jet wind. In addition, the planarity of the blast wave degrades as blast wave evolves three dimensionally. Numerical results visually and quantitatively confirm the presence of vortices, jet wind and three-dimensional expansion of the planar blast wave near the exit. Pressure profiles at 90° orientation show flow separation. When cylinder is placed inside, this flow separation is not sustained, but when placed outside the shock tube this flow separation is sustained which causes tensile loading on the sides of the cylinder. Friedlander waves formed due to field explosives in the intermediate-to far-field ranges are replicated in a narrow test region located deep inside the shock tube.
Blast waves generated by improvised explosive devices (IEDs) cause traumatic brain injury (TBI) i... more Blast waves generated by improvised explosive devices (IEDs) cause traumatic brain injury (TBI) in soldiers and civilians. In vivo animal models that use shock tubes are extensively used in laboratories to simulate field conditions, to identify mechanisms of injury, and to develop injury thresholds. In this article, we place rats in different locations along the length of the shock tube (i.e., inside, outside, and near the exit), to examine the role of animal placement location (APL) in the biomechanical load experienced by the animal. We found that the biomechanical load on the brain and internal organs in the thoracic cavity (lungs and heart) varied significantly depending on the APL. When the specimen is positioned outside, organs in the thoracic cavity experience a higher pressure for a longer duration, in contrast to APL inside the shock tube. This in turn will possibly alter the injury type, severity, and lethality. We found that the optimal APL is where the Friedlander waveform is first formed inside the shock tube. Once the optimal APL was determined, the effect of the incident blast intensity on the surface and intracranial pressure was measured and analyzed. Noticeably, surface and intracranial pressure increases linearly with the incident peak overpressures, though surface pressures are significantly higher than the other two. Further, we developed and validated an anatomically accurate finite element model of the rat head. With this model, we determined that the main pathway of pressure transmission to the brain was through the skull and not through the snout; however, the snout plays a secondary role in diffracting the incoming blast wave towards the skull.
Computer Methods in Biomechanics and Biomedical Engineering, 2012
The effectiveness of helmets in extenuating the primary shock waves generated by the explosions o... more The effectiveness of helmets in extenuating the primary shock waves generated by the explosions of improvised explosive devices is not clearly understood. In this work, the role of helmet on the overpressurization and impulse experienced by the head were examined. The shock wave-head interactions were studied under three different cases: (i) unprotected head, (ii) head with helmet but with varying head-helmet gaps and (iii) head covered with helmet and tightly fitting foam pads. The intensification effect was discussed by examining the shock wave flow pattern and verified with experiments. A helmet with a better protection against shock wave is suggested.
Blast waves generated by improvised explosive devices can cause mild, moderate to severe traumati... more Blast waves generated by improvised explosive devices can cause mild, moderate to severe traumatic brain injury in soldiers and civilians. To understand the interactions of blast waves on the head and brain and to identify the mechanisms of injury, compression-driven air shock tubes are extensively used in laboratory settings to simulate the field conditions. The overall goal of this effort is to understand the mechanics of blast wave-head interactions as the blast wave traverses the head/brain continuum. Toward this goal, surrogate head model is subjected to well-controlled blast wave profile in the shock tube environment, and the results are analyzed using combined experimental and numerical approaches. The validated numerical models are then used to investigate the spatiotemporal distribution of stresses and pressure in the human skull and brain. By detailing the results from a series of careful experiments and numerical simulations, this paper demonstrates that: (1) Geometry of the head governs the flow dynamics around the head which in turn determines the net mechanical load on the head. (2) Biomechanical loading of the brain is governed by direct wave transmission, structural deformations, and wave reflections from tissue-material interfaces. (3) Deformation and stress analysis of the skull and brain show that skull flexure and tissue cavitation are possible mechanisms of blast-induced traumatic brain injury.
Uploads
Papers by Aaron Alai