Kenneth Clark - Academia.edu (original) (raw)

Papers by Kenneth Clark

Prescribed burning can be a viable tool for managing forest ecosystems. However, smoke from presc... more Prescribed burning can be a viable tool for managing forest ecosystems. However, smoke from prescribed fires, which often occur in the wildland-urban interface (WUI), can linger in an area for relatively long periods of time and have an adverse effect on human health. Smoke from low-intensity prescribed fires can also reduce visibility over roads and highways in the vicinity of these fires, producing hazardous conditions for transportation. Improved tools that quantitatively predict the potential impacts of smoke are necessary in order to maximize the benefits of prescribed fires and balance the conflicting needs of ecological fire use and effective smoke management.

Fuel treatments represent a significant component of the wildfire mitigation strategy in the Unit... more Fuel treatments represent a significant component of the wildfire mitigation strategy in the United States. However, the lack of research aimed at quantifying the explicit effectiveness of fuel treatments in reducing wildfire intensity and spread rate limits our ability to make educated decisions about the type and placement of these treatments. As part of a larger project designed to address this knowledge gap, an experiment was conducted in the New Jersey Pine Barrens.

This report describes the database used to compile, store, and manage intensive ground-based biom... more This report describes the database used to compile, store, and manage intensive ground-based biometric data collected at research sites in Colorado, Minnesota, New Hampshire, New Jersey, North Carolina, and Wyoming, supporting research activities of the U.S. North American Carbon Program (NACP). This report also provides details of each site, the sampling design and collection standards for biometric measurements, the database design, data summary examples, and the uses of intensive ground-based biometric data. Additional information on location descriptions, data, databases, and documentation may be accessed at http://www.nrs.fs.fed.us/data/lcms.

Boundary Layer Meteorology, Sep 30, 1999

The spatial variability of turbulent flow statistics in the roughness sublayer (RSL) of a uniform... more The spatial variability of turbulent flow statistics in the roughness sublayer (RSL) of a uniform even-aged 14 m (= h) tall loblolly pine forest was investigated experimentally. Using seven existing walkup towers at this stand, high frequency velocity, temperature, water vapour and carbon dioxide concentrations were measured at 15.5 m above the ground surface from October 6 to 10 in 1997. These seven towers were separated by at least 100m from each other. The objective of this study was to examine whether single tower turbulence statistics measurements represent the flow properties of RSL turbulence above a uniform even-aged managed loblolly pine forest as a best-case scenario for natural forested ecosystems. From the intensive space-time series measurements, it was demonstrated that standard deviations of longitudinal and vertical velocities (u, w) and temperature (T) are more planar homogeneous than their vertical flux of momentum (u* 2) and sensible heat (H) counterparts. Also, the measured H is more horizontally homogeneous when compared to fluxes of other scalar entities such as CO2 and water vapour. While the spatial variability in fluxes was significant (>15 %), this unique data set confirmed that single tower measurements represent the canonical" structure of single-point RSL turbulence statistics, especially flux-variance relationships. Implications to extending the moving-equilibrium" hypothesis for RSL flows are discussed. The spatial variability in all RSL flow variables was not constant in time and varied strongly with spatially averaged friction velocity u*, especially when u* was small. It is shown that flow properties derived from two-point temporal statistics such as correlation functions are more sensitive to local variability in leaf area density when compared to single point flow statistics. Specifically, that the local relationship between the reciprocal of the vertical velocity integral time scale (Iw) and the arrival frequency of organized structures (/h) predicted from a mixing-layer theory exhibited dependence on the local leaf area index. The broader implications of these findings to the measurement and modelling of RSL flows are also discussed.

Forestsat2014 Open Conference System, Jul 25, 2014

American Journal of Physiology Heart and Circulatory Physiology, Aug 1, 2001

Endothelin-1 (ET-1) is a potent vasoconstrictor and produces marked pressor responses when given ... more Endothelin-1 (ET-1) is a potent vasoconstrictor and produces marked pressor responses when given systemically. Studies in sheep have demonstrated that during pregnancy the uterine vasculature is refractory to exogenously administered ET-1. We hypothesize that this pregnancy-dependent refractoriness is due to an upregulation of local uterine metabolism of ET-1 and/or ET(B) receptors and/or downregulation of local uterine ET(A) receptors. To investigate these possibilities, 21 nonpregnant and 17 pregnant sheep were used. Dose-response curves to intravenous infusion of ET-1 and phenylephrine were generated for pregnant and nonpregnant sheep. ET-1 infused systemically demonstrated vasoconstriction in the systemic and renal vasculature of pregnant and nonpregnant animals and vasoconstriction in the uterine vasculature of nonpregnant animals. The pregnant animals showed no uterine vascular response to ET-1. In contrast, phenylephrine showed vasoconstriction in the systemic, renal, and uterine circulations in both pregnant and nonpregnant sheep. After experimentation, the animals were euthanized, and tissues were harvested for Western blot and activity analysis of neutral endopeptidase (NEP) or RT-PCR analysis of endothelin-converting enzyme (ECE) and ET(A) and ET(B) receptors. The content and activity of NEP in the uterine and renal vasculature of pregnant and nonpregnant animals were similar. RT-PCR demonstrated the presence of ECE in the uterine vasculature of pregnant and nonpregnant sheep. ET(A) receptor mRNA was significantly reduced in pregnant compared with nonpregnant sheep, whereas ET(B) receptor mRNA remained unchanged. We conclude that the uterine vascular refractoriness seen in the pregnant sheep is due to a downregulation of ET(A) receptors.

Experimental, Feb 1, 1997

We investigate the e¨ect of non-binding pre-play communication in experiments with simple two-pla... more We investigate the e¨ect of non-binding pre-play communication in experiments with simple two-player coordination games. We reproduce the results of other studies in which play converges to a Pareto-dominated equilibrium in the absence of communication, and communication moves outcomes in the direction of the Pareto-dominant equilibrium. However, we provide new results which show that the e¨ectiveness of communication is sensitive to the structure of payo¨s. Our results support an argument put forward by Aumann: agreements to play a Nash equilibrium are fragile when players have a strict preference over their opponent's strategy choice. We also ®nd that informative communication does not necessarily lead to the Pareto-dominant equilibrium.

American Journal of Obstetrics and Gynecology, Feb 28, 1986

The fetus of the pregnant diabetic woman is exposed to hyperglycemia frequently accompanied by ke... more The fetus of the pregnant diabetic woman is exposed to hyperglycemia frequently accompanied by ketoacidosis. Previous studies have demonstrated that ~-hydroxybutyrate, a major ketone body, crosses the ovine placenta in significant amounts, leading to significant reductions in fetal Pac 2 and increased fetal heart rate. In the present study the pregnant ewe was used to evaluate the maternal and fetal cardiovascular and metabolic responses to hyperketonemia in the presence of hyperglycemia and to determine if the combined diabetic insults were more detrimental to the fetus than hyperketonemia alone. A glucose priming dose of 25 gm was administered in the maternal femoral vein followed by a continuous glucose infusion of 200 mg/min to achieve steady maternal plasma glucose levels of 180 mg/dl. Once glucose levels were stable, ~-hydroxybutyrate was infused for 2 hours at a rate of 0.39 mmol/100 ml of uterine blood flow into both left and right uterine arteries. Infusion of glucose alone did not significantly alter fetal cardiovascular and blood gas parameters but did increase the fetal glucose level from 17 ± 4 to 58 ± 8 mg/dl. The simultaneous infusion of ~-hydroxybutyrate and glucose produced Significant decreases in fetal Pao2 and oxygen content as were reported for hyperketonemia alone and significant time-related increases in fetal lactate levels and fetal heart rate. These data suggest that hyperketonemia in the pregnant ewe leads to quantitatively similar changes in oxygenation in both normoglycemic and hyperglycemic fetuses. These observations may in part help explain the increased perinatal mortality in the pregnant woman with uncontrolled diabetes. (AM J OSSTET GVNECOL 1986;154:394-401.)

American Journal of Physiology Regulatory Integrative and Comparative Physiology, Oct 1, 1999

The present study was designed to assess the dose-related effects of platelet-activating factor (... more The present study was designed to assess the dose-related effects of platelet-activating factor (PAF) on systemic, renal, and uterine hemodynamics in nonpregnant sheep and to evaluate how pregnancy might alter these responses. Nonpregnant and pregnant (110 +/- 5 days gestation) ewes were instrumented for conscious measurements of maternal mean arterial pressure (MAP), renal blood flow (RBF), uterine blood flow (UBF), hematocrit, and urinary protein concentration. After recovery, dose-response curves to PAF were generated by systemic infusion at 10, 30, and 100 ng. kg(-1). min(-1) (15 min/dose) into the maternal femoral vein. The above parameters were measured, and renal and uterine vascular resistances (RVR and UVR, respectively) were calculated. In pregnant sheep, PAF increased MAP, RVR, UVR, and urinary protein concentration. We also observed increases in hematocrit, indicative of reduced blood volume secondary to increased systemic microvascular protein permeability. These responses were similar in nonpregnant sheep, with the exception of UVR in nonpregnant ewes being decreased (and thus UBF was increased), whereas in pregnant sheep, UVR was increased, which resulted in decreased UBF. This suggests that pregnancy alters the mechanism of action of PAF within the uterine vasculature in a way that can reduce UBF and thereby potentially compromise placental perfusion.

Fire Technology, 2015

ABSTRACT This study aims to develop a series of robust and efficient methodologies, which can be ... more ABSTRACT This study aims to develop a series of robust and efficient methodologies, which can be applied to understand and estimate firebrand generation and to evaluate firebrand showers close to a fire front. A field scale high intensity prescribed fire was conducted in the New Jersey Pine Barrens in March 2013. Vegetation was characterised with field and remotely sensed data, fire spread and intensity was characterised and meteorological conditions were monitored before and during the burn. Firebrands were collected from different locations in the forest and analysed for mass and size distribution. The majority were found to be bark slices (more than 70%) with substantial amounts of pine and shrub twigs. Shrub layer consumption was evaluated to supplement the firebrand generation study. Bark consumption was studied by measuring the circumference variation at several heights on each of three different pine trees. The variation was in the same order of magnitude as the bark thickness (1-5 mm). Testing and improving the protocol can facilitate the collection of compatible data in a wide range of ecosystems and fire environments, aiding in the development of solutions to prevent structural ignition at the Wildland Urban Interface.

Journal of Applied Physiology, 2014

Are the fastest running speeds achieved using the simple-spring stance mechanics predicted by the... more Are the fastest running speeds achieved using the simple-spring stance mechanics predicted by the classic spring-mass model? We hypothesized that a passive, linear-spring model would not account for the running mechanics that maximize ground force application and speed. We tested this hypothesis by comparing patterns of ground force application across athletic specialization (competitive sprinters vs. athlete nonsprinters, n = 7 each) and running speed (top speeds vs. slower ones). Vertical ground reaction forces at 5.0 and 7.0 m/s, and individual top speeds (n = 797 total footfalls) were acquired while subjects ran on a custom, high-speed force treadmill. The goodness of fit between measured vertical force vs. time waveform patterns and the patterns predicted by the spring-mass model were assessed using the R(2) statistic (where an R(2) of 1.00 = perfect fit). As hypothesized, the force application patterns of the competitive sprinters deviated significantly more from the simple-spring pattern than those of the athlete, nonsprinters across the three test speeds (R(2) <0.85 vs. R(2) ≥ 0.91, respectively), and deviated most at top speed (R(2) = 0.78 ± 0.02). Sprinters attained faster top speeds than nonsprinters (10.4 ± 0.3 vs. 8.7 ± 0.3 m/s) by applying greater vertical forces during the first half (2.65 ± 0.05 vs. 2.21 ± 0.05 body wt), but not the second half (1.71 ± 0.04 vs. 1.73 ± 0.04 body wt) of the stance phase. We conclude that a passive, simple-spring model has limited application to sprint running performance because the swiftest runners use an asymmetrical pattern of force application to maximize ground reaction forces and attain faster speeds.

Advances in forest fire research, 2014

The spatial variability of turbulent flow statistics in the roughness sublayer (RSL) of a uniform... more The spatial variability of turbulent flow statistics in the roughness sublayer (RSL) of a uniform even-aged 14 m (= h) tall loblolly pine forest was investigated experimentally. Using seven existing walkup towers at this stand, high frequency velocity, temperature, water vapour and carbon dioxide concentrations were measured at 15.5 m above the ground surface from October 6 to 10 in 1997. These seven towers were separated by at least 100 m from each other. The objective of this study was to examine whether single tower turbulence statistics measurements represent the flow properties of RSL turbulence above a uniform even-aged managed loblolly pine forest as a best-case scenario for natural forested ecosystems. From the intensive space-time series measurements, it was demonstrated that standard deviations of longitudinal and vertical velocities (σ u , σ w ) and temperature (σ T ) are more planar homogeneous than their vertical flux of momentum (u 2 * ) and sensible heat (H ) counterparts. Also, the measured H is more horizontally homogeneous when compared to fluxes of other scalar entities such as CO 2 and water vapour. While the spatial variability in fluxes was significant (>15%), this unique data set confirmed that single tower measurements represent the 'canonical' structure of single-point RSL turbulence statistics, especially flux-variance relationships. Implications to extending the 'moving-equilibrium' hypothesis for RSL flows are discussed. The spatial variability in all RSL flow variables was not constant in time and varied strongly with spatially averaged friction velocity u * , especially when u * was small. It is shown that flow properties derived from two-point temporal statistics such as correlation functions are more sensitive to local variability in leaf area density when compared to single point flow statistics. Specifically, that the local relationship between the reciprocal of the vertical velocity integral time scale (I w ) and the arrival frequency of organized structures (ū/ h) predicted from a mixing-layer theory exhibited dependence on the local leaf area index. The broader implications of these findings to the measurement and modelling of RSL flows are also discussed.

Journal of Experimental Biology, 2014

Running performance, energy requirements and musculoskeletal stresses are directly related to the... more Running performance, energy requirements and musculoskeletal stresses are directly related to the action-reaction forces between the limb and the ground. For human runners, the force-time patterns from individual footfalls can vary considerably across speed, footstrike and footwear conditions. Here, we used four human footfalls with distinctly different vertical force-time waveform patterns to evaluate whether a basic mechanical model might explain all of them. Our model partitions the body's total mass (1.0M b ) into two invariant mass fractions (lower limb=0.08, remaining body mass=0.92) and allows the instantaneous collisional velocities of the former to vary. The best fits achieved (R 2 range=0.95-0.98, mean=0.97±0.01) indicate that the model is capable of accounting for nearly all of the variability observed in the four waveform types tested: barefoot jog, rear-foot strike run, fore-foot strike run and fore-foot strike sprint. We conclude that different running ground reaction force-time patterns may have the same mechanical basis.

Seminars in Perinatology, 1996

The effects of nicotine are seen in every trimester of pregnancy, from increased spontaneous abor... more The effects of nicotine are seen in every trimester of pregnancy, from increased spontaneous abortions in the first trimester, to increased premature delivery rates and decreased birth weights in the final trimester. The birth weight of a baby is dependent on two factors: the gestational age of the fetus at the time of delivery and the rate of fetal growth. Nicotine has been shown to affect both of these factors. Carbon monoxide, also found in tobacco, forms carboxyhemoglobin, which inhibits the release of oxygen into fetal tissues. Nicotine readily gains access to the fetal compartment via the placenta, with fetal concentrations generally 15% higher than maternal levels. The primary metabolite of nicotine, cotinine, has a half-life of 15 to 20 hours and serum concentrations that are 10-fold higher than nicotine; thus, cotinlne provides a better index of nicotine exposure because of its longer half-life. Nicotine concentrates in fetal blood, amniotic fluid, and breastmilk. The fetus and neonate may also have environmental tobacco exposure that may be significant. In animal models and humans, nicotine increases maternal blood pressure and heart rate, with a concomitant reduction in uterine blood flow. An increase in fetal heart rate is also seen, which is thought to be caused by catecholamine release. The impact of nicotine on the respiratory and central nervous system is also reviewed. In conclusion, the physiological effect of tobacco on fetal growth seems to be a culmination of both the vasoconstricfive effects of nicotine on the uterine and potentially the umbilical artery and the effects on oxygenation by carboxyhemoglobin.

Neonatology, 1987

Fetal beta-endorphin release has been associated with fetal hypoxia. The purpose of this study wa... more Fetal beta-endorphin release has been associated with fetal hypoxia. The purpose of this study was to assess the degree of uterine blood flow reduction needed to elicit fetal beta-endorphin release in the sheep since there is a large reserve of oxygen supply to the fetus. Uterine blood flow was reduced by 26 +/- 2, 46 +/- 3 and 66 +/- 2%, producing fetal oxygen content concentrations of 5.7 +/- 0.6, 4.4 +/- 0.7 and 2.6 +/- 0.3 ml/dl, respectively. Although fetal oxygen concentrations were significantly decreased in the groups with a reduction in uterine blood flow of 46 and 66%, beta-endorphin was elevated only in the latter group. It is speculated that fetal beta-endorphin is released at a level of hypoxia which leads to a decrease in fetal oxygen consumption. A reduction in uterine blood flow of 66% appears to produce a stressful environment for the fetus as measured by fetal plasma beta-endorphin levels.

Life Sciences, 1980

... 2655-2661 Pergamon Press Printed in the USA EFFECT OF SEROTONIN ON UTERINE BLOOD FLOW IN PREG... more ... 2655-2661 Pergamon Press Printed in the USA EFFECT OF SEROTONIN ON UTERINE BLOOD FLOW IN PREGNANT AND NONPREGNANT SHEEP Kenneth E. Clark, E. Gay Mills, Thomas E. Otte and Stanley J. Stys Departments of ... 13. JB JONES and A. ROWSELL, J. of Ob. ...

Prescribed burning can be a viable tool for managing forest ecosystems. However, smoke from presc... more Prescribed burning can be a viable tool for managing forest ecosystems. However, smoke from prescribed fires, which often occur in the wildland-urban interface (WUI), can linger in an area for relatively long periods of time and have an adverse effect on human health. Smoke from low-intensity prescribed fires can also reduce visibility over roads and highways in the vicinity of these fires, producing hazardous conditions for transportation. Improved tools that quantitatively predict the potential impacts of smoke are necessary in order to maximize the benefits of prescribed fires and balance the conflicting needs of ecological fire use and effective smoke management.

Fuel treatments represent a significant component of the wildfire mitigation strategy in the Unit... more Fuel treatments represent a significant component of the wildfire mitigation strategy in the United States. However, the lack of research aimed at quantifying the explicit effectiveness of fuel treatments in reducing wildfire intensity and spread rate limits our ability to make educated decisions about the type and placement of these treatments. As part of a larger project designed to address this knowledge gap, an experiment was conducted in the New Jersey Pine Barrens.

This report describes the database used to compile, store, and manage intensive ground-based biom... more This report describes the database used to compile, store, and manage intensive ground-based biometric data collected at research sites in Colorado, Minnesota, New Hampshire, New Jersey, North Carolina, and Wyoming, supporting research activities of the U.S. North American Carbon Program (NACP). This report also provides details of each site, the sampling design and collection standards for biometric measurements, the database design, data summary examples, and the uses of intensive ground-based biometric data. Additional information on location descriptions, data, databases, and documentation may be accessed at http://www.nrs.fs.fed.us/data/lcms.

Boundary Layer Meteorology, Sep 30, 1999

The spatial variability of turbulent flow statistics in the roughness sublayer (RSL) of a uniform... more The spatial variability of turbulent flow statistics in the roughness sublayer (RSL) of a uniform even-aged 14 m (= h) tall loblolly pine forest was investigated experimentally. Using seven existing walkup towers at this stand, high frequency velocity, temperature, water vapour and carbon dioxide concentrations were measured at 15.5 m above the ground surface from October 6 to 10 in 1997. These seven towers were separated by at least 100m from each other. The objective of this study was to examine whether single tower turbulence statistics measurements represent the flow properties of RSL turbulence above a uniform even-aged managed loblolly pine forest as a best-case scenario for natural forested ecosystems. From the intensive space-time series measurements, it was demonstrated that standard deviations of longitudinal and vertical velocities (u, w) and temperature (T) are more planar homogeneous than their vertical flux of momentum (u* 2) and sensible heat (H) counterparts. Also, the measured H is more horizontally homogeneous when compared to fluxes of other scalar entities such as CO2 and water vapour. While the spatial variability in fluxes was significant (>15 %), this unique data set confirmed that single tower measurements represent the canonical" structure of single-point RSL turbulence statistics, especially flux-variance relationships. Implications to extending the moving-equilibrium" hypothesis for RSL flows are discussed. The spatial variability in all RSL flow variables was not constant in time and varied strongly with spatially averaged friction velocity u*, especially when u* was small. It is shown that flow properties derived from two-point temporal statistics such as correlation functions are more sensitive to local variability in leaf area density when compared to single point flow statistics. Specifically, that the local relationship between the reciprocal of the vertical velocity integral time scale (Iw) and the arrival frequency of organized structures (/h) predicted from a mixing-layer theory exhibited dependence on the local leaf area index. The broader implications of these findings to the measurement and modelling of RSL flows are also discussed.

Forestsat2014 Open Conference System, Jul 25, 2014

American Journal of Physiology Heart and Circulatory Physiology, Aug 1, 2001

Endothelin-1 (ET-1) is a potent vasoconstrictor and produces marked pressor responses when given ... more Endothelin-1 (ET-1) is a potent vasoconstrictor and produces marked pressor responses when given systemically. Studies in sheep have demonstrated that during pregnancy the uterine vasculature is refractory to exogenously administered ET-1. We hypothesize that this pregnancy-dependent refractoriness is due to an upregulation of local uterine metabolism of ET-1 and/or ET(B) receptors and/or downregulation of local uterine ET(A) receptors. To investigate these possibilities, 21 nonpregnant and 17 pregnant sheep were used. Dose-response curves to intravenous infusion of ET-1 and phenylephrine were generated for pregnant and nonpregnant sheep. ET-1 infused systemically demonstrated vasoconstriction in the systemic and renal vasculature of pregnant and nonpregnant animals and vasoconstriction in the uterine vasculature of nonpregnant animals. The pregnant animals showed no uterine vascular response to ET-1. In contrast, phenylephrine showed vasoconstriction in the systemic, renal, and uterine circulations in both pregnant and nonpregnant sheep. After experimentation, the animals were euthanized, and tissues were harvested for Western blot and activity analysis of neutral endopeptidase (NEP) or RT-PCR analysis of endothelin-converting enzyme (ECE) and ET(A) and ET(B) receptors. The content and activity of NEP in the uterine and renal vasculature of pregnant and nonpregnant animals were similar. RT-PCR demonstrated the presence of ECE in the uterine vasculature of pregnant and nonpregnant sheep. ET(A) receptor mRNA was significantly reduced in pregnant compared with nonpregnant sheep, whereas ET(B) receptor mRNA remained unchanged. We conclude that the uterine vascular refractoriness seen in the pregnant sheep is due to a downregulation of ET(A) receptors.

Experimental, Feb 1, 1997

We investigate the e¨ect of non-binding pre-play communication in experiments with simple two-pla... more We investigate the e¨ect of non-binding pre-play communication in experiments with simple two-player coordination games. We reproduce the results of other studies in which play converges to a Pareto-dominated equilibrium in the absence of communication, and communication moves outcomes in the direction of the Pareto-dominant equilibrium. However, we provide new results which show that the e¨ectiveness of communication is sensitive to the structure of payo¨s. Our results support an argument put forward by Aumann: agreements to play a Nash equilibrium are fragile when players have a strict preference over their opponent's strategy choice. We also ®nd that informative communication does not necessarily lead to the Pareto-dominant equilibrium.

American Journal of Obstetrics and Gynecology, Feb 28, 1986

The fetus of the pregnant diabetic woman is exposed to hyperglycemia frequently accompanied by ke... more The fetus of the pregnant diabetic woman is exposed to hyperglycemia frequently accompanied by ketoacidosis. Previous studies have demonstrated that ~-hydroxybutyrate, a major ketone body, crosses the ovine placenta in significant amounts, leading to significant reductions in fetal Pac 2 and increased fetal heart rate. In the present study the pregnant ewe was used to evaluate the maternal and fetal cardiovascular and metabolic responses to hyperketonemia in the presence of hyperglycemia and to determine if the combined diabetic insults were more detrimental to the fetus than hyperketonemia alone. A glucose priming dose of 25 gm was administered in the maternal femoral vein followed by a continuous glucose infusion of 200 mg/min to achieve steady maternal plasma glucose levels of 180 mg/dl. Once glucose levels were stable, ~-hydroxybutyrate was infused for 2 hours at a rate of 0.39 mmol/100 ml of uterine blood flow into both left and right uterine arteries. Infusion of glucose alone did not significantly alter fetal cardiovascular and blood gas parameters but did increase the fetal glucose level from 17 ± 4 to 58 ± 8 mg/dl. The simultaneous infusion of ~-hydroxybutyrate and glucose produced Significant decreases in fetal Pao2 and oxygen content as were reported for hyperketonemia alone and significant time-related increases in fetal lactate levels and fetal heart rate. These data suggest that hyperketonemia in the pregnant ewe leads to quantitatively similar changes in oxygenation in both normoglycemic and hyperglycemic fetuses. These observations may in part help explain the increased perinatal mortality in the pregnant woman with uncontrolled diabetes. (AM J OSSTET GVNECOL 1986;154:394-401.)

American Journal of Physiology Regulatory Integrative and Comparative Physiology, Oct 1, 1999

The present study was designed to assess the dose-related effects of platelet-activating factor (... more The present study was designed to assess the dose-related effects of platelet-activating factor (PAF) on systemic, renal, and uterine hemodynamics in nonpregnant sheep and to evaluate how pregnancy might alter these responses. Nonpregnant and pregnant (110 +/- 5 days gestation) ewes were instrumented for conscious measurements of maternal mean arterial pressure (MAP), renal blood flow (RBF), uterine blood flow (UBF), hematocrit, and urinary protein concentration. After recovery, dose-response curves to PAF were generated by systemic infusion at 10, 30, and 100 ng. kg(-1). min(-1) (15 min/dose) into the maternal femoral vein. The above parameters were measured, and renal and uterine vascular resistances (RVR and UVR, respectively) were calculated. In pregnant sheep, PAF increased MAP, RVR, UVR, and urinary protein concentration. We also observed increases in hematocrit, indicative of reduced blood volume secondary to increased systemic microvascular protein permeability. These responses were similar in nonpregnant sheep, with the exception of UVR in nonpregnant ewes being decreased (and thus UBF was increased), whereas in pregnant sheep, UVR was increased, which resulted in decreased UBF. This suggests that pregnancy alters the mechanism of action of PAF within the uterine vasculature in a way that can reduce UBF and thereby potentially compromise placental perfusion.

Fire Technology, 2015

ABSTRACT This study aims to develop a series of robust and efficient methodologies, which can be ... more ABSTRACT This study aims to develop a series of robust and efficient methodologies, which can be applied to understand and estimate firebrand generation and to evaluate firebrand showers close to a fire front. A field scale high intensity prescribed fire was conducted in the New Jersey Pine Barrens in March 2013. Vegetation was characterised with field and remotely sensed data, fire spread and intensity was characterised and meteorological conditions were monitored before and during the burn. Firebrands were collected from different locations in the forest and analysed for mass and size distribution. The majority were found to be bark slices (more than 70%) with substantial amounts of pine and shrub twigs. Shrub layer consumption was evaluated to supplement the firebrand generation study. Bark consumption was studied by measuring the circumference variation at several heights on each of three different pine trees. The variation was in the same order of magnitude as the bark thickness (1-5 mm). Testing and improving the protocol can facilitate the collection of compatible data in a wide range of ecosystems and fire environments, aiding in the development of solutions to prevent structural ignition at the Wildland Urban Interface.

Journal of Applied Physiology, 2014

Are the fastest running speeds achieved using the simple-spring stance mechanics predicted by the... more Are the fastest running speeds achieved using the simple-spring stance mechanics predicted by the classic spring-mass model? We hypothesized that a passive, linear-spring model would not account for the running mechanics that maximize ground force application and speed. We tested this hypothesis by comparing patterns of ground force application across athletic specialization (competitive sprinters vs. athlete nonsprinters, n = 7 each) and running speed (top speeds vs. slower ones). Vertical ground reaction forces at 5.0 and 7.0 m/s, and individual top speeds (n = 797 total footfalls) were acquired while subjects ran on a custom, high-speed force treadmill. The goodness of fit between measured vertical force vs. time waveform patterns and the patterns predicted by the spring-mass model were assessed using the R(2) statistic (where an R(2) of 1.00 = perfect fit). As hypothesized, the force application patterns of the competitive sprinters deviated significantly more from the simple-spring pattern than those of the athlete, nonsprinters across the three test speeds (R(2) <0.85 vs. R(2) ≥ 0.91, respectively), and deviated most at top speed (R(2) = 0.78 ± 0.02). Sprinters attained faster top speeds than nonsprinters (10.4 ± 0.3 vs. 8.7 ± 0.3 m/s) by applying greater vertical forces during the first half (2.65 ± 0.05 vs. 2.21 ± 0.05 body wt), but not the second half (1.71 ± 0.04 vs. 1.73 ± 0.04 body wt) of the stance phase. We conclude that a passive, simple-spring model has limited application to sprint running performance because the swiftest runners use an asymmetrical pattern of force application to maximize ground reaction forces and attain faster speeds.

Advances in forest fire research, 2014

The spatial variability of turbulent flow statistics in the roughness sublayer (RSL) of a uniform... more The spatial variability of turbulent flow statistics in the roughness sublayer (RSL) of a uniform even-aged 14 m (= h) tall loblolly pine forest was investigated experimentally. Using seven existing walkup towers at this stand, high frequency velocity, temperature, water vapour and carbon dioxide concentrations were measured at 15.5 m above the ground surface from October 6 to 10 in 1997. These seven towers were separated by at least 100 m from each other. The objective of this study was to examine whether single tower turbulence statistics measurements represent the flow properties of RSL turbulence above a uniform even-aged managed loblolly pine forest as a best-case scenario for natural forested ecosystems. From the intensive space-time series measurements, it was demonstrated that standard deviations of longitudinal and vertical velocities (σ u , σ w ) and temperature (σ T ) are more planar homogeneous than their vertical flux of momentum (u 2 * ) and sensible heat (H ) counterparts. Also, the measured H is more horizontally homogeneous when compared to fluxes of other scalar entities such as CO 2 and water vapour. While the spatial variability in fluxes was significant (>15%), this unique data set confirmed that single tower measurements represent the 'canonical' structure of single-point RSL turbulence statistics, especially flux-variance relationships. Implications to extending the 'moving-equilibrium' hypothesis for RSL flows are discussed. The spatial variability in all RSL flow variables was not constant in time and varied strongly with spatially averaged friction velocity u * , especially when u * was small. It is shown that flow properties derived from two-point temporal statistics such as correlation functions are more sensitive to local variability in leaf area density when compared to single point flow statistics. Specifically, that the local relationship between the reciprocal of the vertical velocity integral time scale (I w ) and the arrival frequency of organized structures (ū/ h) predicted from a mixing-layer theory exhibited dependence on the local leaf area index. The broader implications of these findings to the measurement and modelling of RSL flows are also discussed.

Journal of Experimental Biology, 2014

Running performance, energy requirements and musculoskeletal stresses are directly related to the... more Running performance, energy requirements and musculoskeletal stresses are directly related to the action-reaction forces between the limb and the ground. For human runners, the force-time patterns from individual footfalls can vary considerably across speed, footstrike and footwear conditions. Here, we used four human footfalls with distinctly different vertical force-time waveform patterns to evaluate whether a basic mechanical model might explain all of them. Our model partitions the body's total mass (1.0M b ) into two invariant mass fractions (lower limb=0.08, remaining body mass=0.92) and allows the instantaneous collisional velocities of the former to vary. The best fits achieved (R 2 range=0.95-0.98, mean=0.97±0.01) indicate that the model is capable of accounting for nearly all of the variability observed in the four waveform types tested: barefoot jog, rear-foot strike run, fore-foot strike run and fore-foot strike sprint. We conclude that different running ground reaction force-time patterns may have the same mechanical basis.

Seminars in Perinatology, 1996

The effects of nicotine are seen in every trimester of pregnancy, from increased spontaneous abor... more The effects of nicotine are seen in every trimester of pregnancy, from increased spontaneous abortions in the first trimester, to increased premature delivery rates and decreased birth weights in the final trimester. The birth weight of a baby is dependent on two factors: the gestational age of the fetus at the time of delivery and the rate of fetal growth. Nicotine has been shown to affect both of these factors. Carbon monoxide, also found in tobacco, forms carboxyhemoglobin, which inhibits the release of oxygen into fetal tissues. Nicotine readily gains access to the fetal compartment via the placenta, with fetal concentrations generally 15% higher than maternal levels. The primary metabolite of nicotine, cotinine, has a half-life of 15 to 20 hours and serum concentrations that are 10-fold higher than nicotine; thus, cotinlne provides a better index of nicotine exposure because of its longer half-life. Nicotine concentrates in fetal blood, amniotic fluid, and breastmilk. The fetus and neonate may also have environmental tobacco exposure that may be significant. In animal models and humans, nicotine increases maternal blood pressure and heart rate, with a concomitant reduction in uterine blood flow. An increase in fetal heart rate is also seen, which is thought to be caused by catecholamine release. The impact of nicotine on the respiratory and central nervous system is also reviewed. In conclusion, the physiological effect of tobacco on fetal growth seems to be a culmination of both the vasoconstricfive effects of nicotine on the uterine and potentially the umbilical artery and the effects on oxygenation by carboxyhemoglobin.

Neonatology, 1987

Fetal beta-endorphin release has been associated with fetal hypoxia. The purpose of this study wa... more Fetal beta-endorphin release has been associated with fetal hypoxia. The purpose of this study was to assess the degree of uterine blood flow reduction needed to elicit fetal beta-endorphin release in the sheep since there is a large reserve of oxygen supply to the fetus. Uterine blood flow was reduced by 26 +/- 2, 46 +/- 3 and 66 +/- 2%, producing fetal oxygen content concentrations of 5.7 +/- 0.6, 4.4 +/- 0.7 and 2.6 +/- 0.3 ml/dl, respectively. Although fetal oxygen concentrations were significantly decreased in the groups with a reduction in uterine blood flow of 46 and 66%, beta-endorphin was elevated only in the latter group. It is speculated that fetal beta-endorphin is released at a level of hypoxia which leads to a decrease in fetal oxygen consumption. A reduction in uterine blood flow of 66% appears to produce a stressful environment for the fetus as measured by fetal plasma beta-endorphin levels.

Life Sciences, 1980

... 2655-2661 Pergamon Press Printed in the USA EFFECT OF SEROTONIN ON UTERINE BLOOD FLOW IN PREG... more ... 2655-2661 Pergamon Press Printed in the USA EFFECT OF SEROTONIN ON UTERINE BLOOD FLOW IN PREGNANT AND NONPREGNANT SHEEP Kenneth E. Clark, E. Gay Mills, Thomas E. Otte and Stanley J. Stys Departments of ... 13. JB JONES and A. ROWSELL, J. of Ob. ...