Downhill Slope Research Articles

Kinetics of the Forelimb in Horses Trotting an Uphill and Downhill Slope

IntroductionEquine training often includes running on tracks with different uphill (UP) or downhill (DOWN) slopes and examination of lame horses on a slope can be used to investigate the origin of lameness. However little is known about the kinetics of horses in such circumstances. The aim of this study was to quantify and compare ground reaction force, acceleration and sliding of the hoof in the forelimb of horses trotting an uphill and downhill slope.MethodsThe right front hoof of 5 horses was equipped with a dynamometric horseshoe and an accelerometer allowing the measurement of 3D ground reaction force and hoof acceleration and displacement. The horses were trotted in hand (3.5 m/s) on a 7% inclined asphalt area successively uphill and downhill. Data were analysed using an ANOVA, accounting for correlated repeated measurements within each horse (P<0.01).ResultsSpeed was not significantly different between UP and DOWN. The maximal longitudinal breaking force of the hoof, maximal vertical force, vertical impulse and longitudinal sliding of the hoof at impact were significantly increased on DOWN compared to UP (respectively +97.7%, +8.4%, +16.6% and +450%). Stride frequency and longitudinal propulsive force were significantly decreased on DOWN compared to UP (respectively −5.1% and −48.7%).ConclusionsThe results of this study (increased longitudinal breaking force and maximal vertical force on a downward slope) are consistent with previous measurements of superficial digital flexor tendon loading on the same area [1]. Conversely increased propulsive force on an uphill slope needs to be taken into account during rehabilitation of horses with deep digital flexor tendon injuries.Ethical Animal ResearchThe local Animal Care and Ethics Committee advised that no formal approval was required for this study. Sources of funding: Conseil Régional de Basse‐Normandie, the Fonds Unique Interministériel, the French Ministry of Agriculture, the FEDER and the Institut Français du Cheval et de l'Equitation (IFCE). Competing interests: none.

Mapping the geogenic radon potential: methodology and spatial analysis for central Hungary

A detailed geogenic radon potential (GRP) mapping based on field soil gas radon and soil gas permeability measurements was carried out in this study. A conventional continuous variable approach was used in this study for GRP determination and to test its applicability to the selected area of Hungary. Spatial pattern of soil gas radon concentration, soil permeability and GRP and the relationship between geological formations and these parameters were studied by performing detailed spatial analysis.Exploratory data analysis revealed that higher soil gas radon activity concentration and GRP characterizes the mountains and hills than the plains. The highest values were found in the proluvial–deluvial sediments, rock debris on the downhill slopes eroded from hills. Among the Quaternary sediments, which characterize the study area, the fluvial sediment has the highest values, which are also located in the hilly areas. The lowest values were found in the plain areas covered by drift sand, fluvioeolic sand, fluvial sand and loess. As a conclusion, radon is related to the sediment cycle in the study area.A geogenic radon risk map was created, which assists human health risk assessment and risk reduction since it indicates the potential of the source of indoor radon. The map shows that low and medium geogenic radon potential characterizes the study area in central Hungary. High risk occurs only locally. The results reveal that Quaternary sediments are inhomogeneous from a radon point of view, fluvial sediment has medium GRP, whereas the other rock formations such as drift sand, fluioeolic sand, fluvial sand and loess, found in the study area, have low GRP.

Dynamics, stability, and actuation methods for powered compass gait walkers

In this paper, methods to achieve actively powered walking on level ground using a simple 2-dimensional walking model (compass-gait walker) are explored. The walker consists of 2 massless legs connected at the hip joint, a point mass at the hip, and an infinitesimal point mass at the feet. The walker is actuated either by applying equal joint torques at the hip and ankle, by an impulse applied at the toe off, immediately before the heel strike, or by the combination of both. It is shown that actuating the walker by equal joint torques at the hip and ankle on level ground is equivalent to the dynamics of the passive walker on a downhill slope. The gait cycle for the simplified walker model is determined analytically for a given initial stance angle. Stability of the gait cycle by an analytical approximation to the Jacobian of the walking map is calculated. The results indicate that the short-period cycle always has an unstable eigenvalue, whereas stability of the long-period cycle depends on selection of the initial stance angle. The effect of the torso mass by adding a third link attached at the hip joint is investigated. The torso link is kept in the vertical position by controlling the torque applied to it. The proportional-derivative control law is utilized to regulate the angular position error of the torso link. Using linearized dynamics for this walker, active control is applied to the ankle, which reduces the dynamics of the walker to the passive walker without the torso. The proposed walker is capable of producing stable walking while keeping the torso in an upright position.

Passive prosthetic ankle-foot mechanism for automatic adaptation to sloped surfaces.

This article describes the development of a prototype prosthetic ankle-foot system that passively adapts to surface slopes on each step of walking. Engineering analyses were performed to design the cam clutch and clutch engagement and disengagement mechanism. The prototype was tested by a veteran with a unilateral transtibial amputation. Kinematic and kinetic data were recorded while the subject walked on a treadmill at slopes ranging from -10 degrees to +10 degrees. After each slope condition, the subject rated his level of exertion and socket comfort. The subject reported increased comfort and reduced exertion for downhill slopes when using the prototype compared with his usual prosthesis. The subject also expressed that when walking downhill on the prototype, it was the most comfortable he has ever been in a prosthesis. The prosthetic ankle torque-angle relationship shifted toward dorsiflexion for uphill and toward plantar flexion for downhill slopes when using the prototype, indicating slope adaptation, but this effect did not occur when the subject walked with his usual prosthesis. The prototype also demonstrated late-stance plantar flexion, suggesting the potential for storing and returning more energy than standard lower-limb prostheses.

Freak waves in weakly nonlinear unidirectional wave trains over a sloping bottom in shallow water

Using a Boussinesq model with improved linear dispersion, we show numerical evidence that bottom non-uniformity can provoke significantly increased probability of freak waves as a wave field propagates into shallower water, in agreement with recent experimental results [K. Trulsen, H. Zeng, and O. Gramstad, “Laboratory evidence of freak waves provoked by non-uniform bathymetry,” Phys. Fluids 24, 097101 (2012)]. Increased values of skewness, kurtosis, and probability of freak waves can be found on the shallower side of a bottom slope, with a maximum close to the end of the slope. The increased probability of freak waves is typically seen to endure some distance into the shallower domain, before it decreases and reaches a stable value depending on the depth. The maxima of the statistical parameters are observed both in the case where there is a region of constant depth after the slope, and in the case where the uphill slope is immediately followed by a downhill slope. In the case that waves propagate over a slope from shallower to deeper water, however, we do not find any increase in freak wave occurrence.

Foreshortening affects both uphill and downhill slope perception at far distances

Perceived slope varies with the viewing distance, and is consistent with the effects of foreshortening. Distant viewing makes uphill slopes appear steeper and downhill slopes flatter than does near viewing. These effects are obvious to skiers and climbers in mountainous country. They have also been measured in outdoor experiments with controlled viewing distances. There are many other sources of slope illusions.

Energy Consumption Prediction of a Vehicle along a User-Specified Real-World Trip

Standard cycles provide an easy way to evaluate the energy consumption of vehicles, but it is the energy consumption that occurs on real-world trips that really matters to the driver and, to a larger extent, society. This study shows how digital maps and vehicle simulation tools can be used to estimate energy consumption on a real-world trip. The user (1) selects a trip in the mapping service ADAS-RP (Advanced Driver Assistance Systems Research Platform), (2) defines a vehicle model in the vehicle powertrain simulation tool Autonomie, and (3) runs and analyzes the simulation in that same tool. For each section of the trip, ADAS-RP provides various information that can include speed limits, historic data on traffic pattern speeds, the slopes of the routes, and the positions of stop signs and traffic lights. The first stage of processing this information is to schedule the stops and to create an intermediate speed target that takes those stops into account. The final driver demand speed includes transitions – accelerations and decelerations – between sections with different intermediate speed targets, or around stops. The ADAS-RP/Autonomie process is then used to compute the energy consumption of a hybrid electric vehicle and a conventional vehicle on 10 trips defined across the United States and Germany. The hybrid vehicle is more fuel efficient, especially on congested routes and routes with downhill slopes, the effect of which is analyzed in further detail.

Changes in kernel characteristics during grain filling in silage-specific and dual-purpose corn hybrids

Ma, B. L. and Dwyer, L. M. 2012. Changes in kernel characteristics during grain filling in silage-specific and dual-purpose corn hybrids. Can. J. Plant Sci. 92: 427–439. Silage-specific corn (Zea mays L.) hybrids have been gaining in popularity in recent years, but there is a lack of information about the difference in kernel characterization between Leafy silage-specific and dual-purpose hybrids. A field study was conducted for 4 yr to determine the changes in kernel moisture content, kernel dry weight, kernel nitrogen (N) and phosphorus (P) concentrations over the period of grain filling for Leafy silage-specific and dual-purpose hybrids at two plant population densities. In both types of hybrids, kernel dry weight content increased rapidly from approximately 2 wk after silking and reached a maximum at about 50 to 68 d after silking. While some differences among hybrids in kernel maximum dry weight were noted (P<0.05), there was no distinction between hybrid types. The coefficients of kernel moisture change differed greatly between the two types with lower rates of decline of kernel moisture in some of the Leafy silage-specific hybrids (down-hill slope b<0.0136±0.00044 g kg−1d−1) than the dual-purpose or silage hybrids without the Leafy characteristic (b≥0.0164±0.00039 g kg−1d−1). Higher plant population density had a negligible effect on kernel moisture decline and N and P concentrations, but reduced kernel dry weight by up to 7% in one year. Kernel P was linearly positively correlated with N content (r>0.79, P<0.01), and there was a linear relationship between kernel moisture and the whole-plant silage moisture content (R2≥0.70). Our data also showed that one of the Leafy silage-specific hybrids had higher rates of kernel dry weight accumulation and softer kernel hardness (P<0.05) than the dual-purpose or non-Leafy silage hybrids. Our findings on the distinct characteristics of hybrid types are important considerations for corn producers to choose suitable hybrids and make decisions on silage harvest dates.

Fuzzy optimal schedule of high speed train operation to minimize energy consumption with uncertain delays and driver's behavioral response

Energy efficiency is an important concern in for railway administrations and operators. Strategies focused on traffic operation can achieve energy savings in short term and with associated low investments. For that purpose the main strategies are the design of efficient timetables and driving (ecodriving). The ecodriving applies coasting commands (null traction force) to reduce energy consumption, taking into account downhill slopes, speed reductions, etc. (Acikbas and Soylemez, 2008). However, timetable models in literature do not typically consider energy minimization as a goal, and punctuality requirements under uncertainty. In this paper a model for the joint design of ecodriving and timetable under uncertainty for high speed lines is proposed where the railway operator and administrator requirements are incorporated. Uncertainty in delays is modeled as fuzzy numbers and punctuality constraints, and the timetable optimization model is a fuzzy linear programming model, in which the objective function includes the consumptions of delayed scenarios and the behavioral response of the driver that will affect the consumption. The ecodriving design is based on a Genetic Algorithm that makes use of a detailed simulation model, taking into account the specific characteristics of high speed lines and trains. The proposed method is applied to a real Spanish high speed line to optimize the operation and it is compared to the current commercial service in order to evaluate the potential energy savings.

착지 높이와 지면 형태가 하지 관절에 미치는 영향

In this study, the lower limbs joints were analyzed for features based on the biomechanical characteristics of landing techniques according to height and landing on the ground type (flats and downhill). In order to achieve the objectives of the study, changes were analyzed in detail contents such as the height and form of the first landing on the ground at different angles of joints, torso and legs, torso and legs of the difference in the range of angular motion of the joint, the maximum angular difference between joints, the lower limbs joints difference between the maximum moment and the difference between COM changes. The subjects in this study do not last six months did not experience joint injuries 10 males in 20 aged were tested. Experimental tools to analyze were the recording and video equipment. Samsung`s SCH-650A model camera was used six units, and the 2 GRF-based AMTI were used BP400800 model. 6-unit-camera synchronized with LED (photo cell) and Line Lock system were used. the output from the camera and the ground reaction force based on the data to synchronize A/D Syc. box was used. To calculate the coordinates of three-dimensional space, (X, Y, Z axis) to the size of the control points attached to the framework of 36 markers were used, and 29 where the body was taken by attaching a marker to the surface. Two kinds of land condition, 40cm and 60cm in height, and ground conditions in the form of two kinds of flat and downhill slopes () of the landing operation was performed and each subject`s 3 mean two-way RM ANOVA in SPSS 18.0 was used and this time, all the significant level was set at a

Israeli rejectionism: a hidden agenda in the Middle East peace process

Introduction 1: Palestine - Homeland for the Jews? 2: The Partition of Palestine 3: Early Initiatives 4: The Lull in Hostilities 1956-1967 5: The aftermath of the June 1967 war 6: From Yom Kippur to Lebanon 7: From Lebanon to Oslo 8: PLO as Peace Partner? 9: Barak Leaves No Stone Unturned 10: Peace on a Downhill Slope Conclusion Chronology Bibliography Index

남자 골프 선수의 경사면의 차이에 따른 스윙동작에 대한 운동학적 비교 분석

The main objective of this research was to develop a method which could be used to get the ultimate golf-swing and improve the ability of performing them. This will be shall by using a comparative analysis of the male progolfers` swing movements and the angles taken with each shot, especially at 0, 10, and -10 degree slopes. As a result of using advanced image analysis equipment to analyze each golf swing at the slope, we conclude as following. First, it appears that there is no difference in the entire swing time and the time it takes to perform each step of the proper hitting form. As a result, regardless of slope (whether it is 0, 10, or -10 degrees) the total swing time is all the same. Second, the experiment shows the following results. -The displacement of body`s center of gravity at each slope is not a variable. - The direction of the ball when hit will vary from each slope. - When hitting from a slope, the original center of gravity for a body after the ball was hit, moved about 8.45cm from the place where the shot was taken. That is a 62.36% change from the original center of gravity, which was found by calculating the total movement of gravity. -If you have a slope, the average body movement was restricted by 8%. -It shows that the movement in the upper and lower parts of your body will have a significant effect on the shot when hitting from a slope. Third, the experiment shows the following results. -When hitting from the slope, the angle of the right knee after the shot always differed from the original angle of the right knee, but when shooting from 10, 0, and -10 degree angles, the 10 had the most change, while the 0 and -10 degree shots followed, respectively. - The difference of the angle in the left knee from the original stance had the most change during the downswing to impact. Fourthly, the experiment shows the following results. -The speed of the club reached its peak just before impact regardless of the slope, which means the top speed of the club in the slope of 0 degree is faster than those of the 10 and -10 degree. 0 degrees resulted in 29.7 m/s 10 degrees resulted in 27.6 m/s -10 degrees resulted in 28.1 m/s Comparing the results of each slope to the shot taken from 0 degrees, the top speed of the club decreased by an average of 5% at the downhill slope whilst the uphill slope decreased by an average 7%. Finally, the experiment shows the following results. Shooting from a 0 degree angle resulted in a speed of 56.5m/s. Shooting from a 10 degree angle resulted in a speed of 54.3m/s. Shooting from a -10 degree angle resulted in a speed of 55.8m/s. Compared to the shot taken at the flat slope (0 degrees), the ball speed will decrease by 1.3% when shooting from a downward slope, and it will decrease by 4% when shooting from an upward slope. This means that shooting from a flat surface will give you the best results.

GIS‐evaluation of two slope‐calculation methods regarding their suitability in slope analysis using high‐precision LiDAR digital elevation models

AbstractSlope is a metric that is essential to describe surface hydrological processes, including overland flow, soil erosion, and sediment transport. Most commercial GIS have built‐in functions to calculate the slope from Digital Elevation Models (DEMs) by means of average neighbourhood methods that are appropriate for coarse‐resolution DEMs. Emergence of high‐resolution DEMs from LiDAR data creates a need to re‐assess the suitability of existing algorithms for calculating slope in hydrological applications.In this study, we investigate the properties of two different slope‐calculation methods: an average‐neighbourhood‐slope (ANS) and a downhill‐slope (DHS) method. Conceptually, the DHS method provides a more intuitive description of surface water‐flow characteristics in an uneven terrain. DEMs of five different types were used to evaluate the methods, namely a 1‐m and 10‐m resolution DEM interpolated from irregular elevation point‐data generated with conventional photogrammetric techniques, and a 1‐m, 5‐m, and 10‐m resolution DEM derived from LiDAR data. The slopes calculated were summarized for the entire watershed, along mapped streams, and within pre‐defined ‘stream buffers’. Slopes generated for the entire watershed with 1‐m resolution LiDAR DEM indicated that the ANS method on an average produced smaller slopes than the DHS method (0·64°). A similar trend was observed in stream buffers, with greatest slope differences (ΔS) between methods within 20‐m buffers, when the 1‐m LiDAR‐based DEM was used (ΔS = 1·12°). In contrast, the ANS‐calculated slopes along mapped streams were generally larger than those calculated with the DHS method for LiDAR‐based DEMs (ΔS = 0·81°). The results from this study signal the need for caution when estimating slopes along streams from high‐accuracy, LiDAR‐generated DEMs. Copyright © 2011 John Wiley & Sons, Ltd.

The Effects of an Acute Overspeed Warm-Up on Sprint Performance in Collegiate Athletes

Overspeed training, which can be performed in various ways including the use of elastic cords or downhill slopes, accelerates the athlete to speeds above that which they could achieve in flat running. To date, no known research has directly examined the use of overspeed techniques in a warm-up to improve sprint performance. PURPOSE: To determine whether an acute overspeed warm-up before a short sprint (60 M) can improve running speed. It was hypothesized that overspeed warm-ups would improve running speed compared to a traditional warm-up. METHODS: Participants (N = 23, 12 female) completed two days of testing which consisted of a 10-15 warm-up followed by one timed and videotaped 60 M dash. The overspeed intervention consisted of 4 30 M bungee runs done following the warm-up and before the 60 M sprint. The order of the intervention was randomized and counterbalanced. RESULTS: A 2 (condition) by 3 (segment; 0-20M, 20-40M, 40-60M) repeated measures GLM for time revealed a significant segment effect but no significant condition effect, F(2, 40) = 500.62, p <.01. Time was significantly greater for the first 20 meters (3.36± 0.05) than the second 20 meters (2.41±0.03) or the third 20 meters (2.46±0.05). The times for segment 2 and 3 were not different. The condition by segment interaction failed to reach significance, F(2, 44) = 3.07, p =.08. A 2 (condition) by 4 (segment; 0-10M, 10-20M, 25-35M, 45-55M) repeated measures GLM for stride length revealed a significant segment effect but no significant condition effect or condition by segment interaction, F(3, 60) = 287.06, p <.01. Stride length in meters from 0-10M (1.37 M) was shorter than that from 10-20M (1.86 M), 25-35M (2.06 M), and 45-55M (2.10 M). Stride length from 10-20M was shorter than that from 25-35M and 45-55M while there was no difference between 25-35M and 45-55M. CONCLUSION: While no significant differences were found between the overspeed warm-up and the traditional warm up, absolute differences were observed. It is possible that this small difference could have an impact on performance. Future research should incorporate more subjects and athletes who are familiar with overspeed techniques to determine the magnitude of this absolute difference.

Effects of Load and Gradient on Energy Cost of Running

This study quantified the interaction of electromyography (EMG) obtained from the vastus lateralis and metabolic energy cost of running (C(r); mL·[mass+load](-1)·meter(-1)), an index of running economy, during submaximal treadmill running. Experiments were conducted with and without load on the back on a motor-driven treadmill on the downhill, level and uphill slopes. The obtained EMG was full-wave rectified and integrated (iEMG). The iEMG was divided into eccentric (ECC) and concentric (CON) phases with a foot sensor and a knee-joint goniometer. The ratio of ECC to CON (ECC/CON ratio) was regarded as the muscle elastic capacity during running on each slope. The C(r) was determined as the ratio of the 2-min steady-state VO(2) to the running speed. We found a significant decrease in the C(r) when carrying the load at all slopes. The ECC/CON ratio was significantly higher in the load condition at the downhill and level slopes, but not at the uphill slope. A significant gradient difference was observed in the C(r) (down<level<up) and ECC/CON ratio (down=level>uphill). Thus, an alteration of Cr by the gradient and load was almost consistent with that of the ECC/CON ratio. The ECC/CON ratio, but not the rotative torque (T) functioning around the center of body mass, significantly correlated with C(r) (r=-0.41, p<0.05). These results indicated that the ECC/CON ratio, rather than T, contributed to one of the energy-saving mechanisms during running with load.

The Epidemiology of Ankle Sprain During Hiking in Uniformed Groups

Purpose To determine the prevalence of ankle sprain during hiking training in uniformed groups and identify the risk factors of ankle sprain and the risk factors associated with residual problems after ankle sprain. Methods A retrospective cross-sectional study involved 590 members of a uniformed group from secondary schools and their leaders by means of a self-administered anonymous questionnaire. Results The prevalence of ankle sprain was 9.15%. Most of them were lateral sprains (70.4%) and occurred in scree ground (51.9%) and downhill slope (50.0%). Subjects who are “older” aged, are overweight, are leaders in uniformed groups, have a past history of ankle sprain or problem, have a long-term lower limb injury, wear inadequate sized or tight shoes, and use hiking poles, have significant risks. The prevalence of having residual problems after ankle sprains was 48.14%, and the most common one was residual ankle pain (25.0%). Conclusion Uniformed group leaders and members should be aware of the risk factors of ankle sprain during hiking training in the countryside. They should also be aware of the importance of proper treatment and rehabilitation to prevent residual ankle problem. Level of Evidence Level II prognostic study.

Energetics and Passive Dynamics of the Ankle in Downhill Walking

This study investigated the energetics of the human ankle during the stance phase of downhill walking with the goal of modeling ankle behavior with a passive spring and damper mechanism. Kinematic and kinetic data were collected on eight male participants while walking down a ramp with inclination varying from 0° to 8°. The ankle joint moment in the sagittal plane was calculated using inverse dynamics. Mechanical energy injected or dissipated at the ankle joint was computed by integrating the power across the duration of the stance phase. The net mechanical energy of the ankle was approximately zero for level walking and monotonically decreased (i.e., became increasingly negative) during downhill walking as the slope decreased. The indication is that the behavior of the ankle is energetically passive during downhill walking, playing a key role in dissipating energy from one step to the next. A passive mechanical model consisting of a pin joint coupled with a revolute spring and damper was fit to the ankle torque and its parameters were estimated for each downhill slope using linear regression. The passive model demonstrated good agreement with actual ankle dynamics as indicated by low root-mean-square error values. These results indicate the stance phase behavior of the human ankle during downhill walking may be effectively duplicated by a passive mechanism with appropriately selected spring and damping characteristics.

Hills look less steep from the edge: Proprioceptive error and frontal tendency affect the perception of downhill slopes

Hills look less steep from the edge: Proprioceptive error and frontal tendency affect the perception of downhill slopes

The Lada Terra rise and Quetzalpetlatl Corona: A region of long-lived mantle upwelling and recent volcanic activity on Venus

Quetzalpetlatl Corona (∼850 km in diameter) and Boala Corona (∼350 km×250 km in diameter), are both situated within the Lada Terra rise, a prominent ∼2000-km-wide circular topographic feature rising ∼2.5–3 km above the mean planetary radius in the southern hemisphere of Venus, south of the Lavinia Planitia lowlands. Together these features form a unique configuration that combines the characteristics of corona-dominated rises (e.g., Eistla), rifted volcanic rises (e.g., Beta Regio), and large coronae structures (such as Artemis and Heng-O). Three zones of extension converge on the central part of the rise at Boala Corona, and hundreds of extensive lava flows emerge from the summit region, stream down the sides of the rise, and flood the surrounding topographic annulus and moat. Detailed geological mapping of the region shows that Cocomama Tessera terrain was flexed, uplifted and flooded during the formation of the Lada rise. Stratigraphic relationships show that the rise formed over an extended period of time following tessera formation. Evidence for early uplift includes flexure of the tessera, formation of the Quetzalpetlatl Corona annular ridge, and the radial array of flows originating from the center of the feature (showing the presence of downhill slopes). Early Quetzalpetlatl Corona activity was focused on the formation of the annular ridge, and the outer moat continued to form throughout the extended history of the rise, deforming even after the emplacement of some of the most recent lavas. Central radial flows ponded behind the early-forming annular ridge, concentrating the load inside the ridge, perhaps adding to the evolution of the moat. Late-stage activity includes final radial flows and central shields inside Boala Corona. On the basis of gravity, topography and image data, volcanism has persisted into the most recent geological era. We compare the central Lada rise with other regions of Venus thought to be currently active on the basis of Venus Express VIRTIS emissivity data and we conclude that although the area may have been active in the very recent geological past, stratigraphic evidence favors an endogenic origin for some VIRTIS anomalies. The coaxial combination of the broad rise of Lada Terra with large coronae (Quetzalpetlatl and Boala) suggests that these two types of features are parts of a continuum related to the magnitude and history of mantle thermal upwellings. We see no evidence that the culmination of this process results in tessera formation.

Long-term impact of de-icing salts on tree health in the Lake Tahoe Basin: Environmental influences and interactions with insects and diseases

Lake Tahoe, on the boundary of California and Nevada, is world renown for its natural beauty and is also a popular location for winter-sporting activities. De-icing compounds, such as sodium chloride (NaCl), are used to maintain safe winter driving conditions. Sodium chloride, however, can damage roadside vegetation and affect surface and ground water quality. Our objectives were to: investigate the relationship among salt damage to trees and other damage (from insects, diseases, and other biotic and abiotic factors), examine the effects of vegetation characteristics and environmental factors on salt damage to trees, and to quantify the long-term impacts of de-icing salts on roadside conifers in the Tahoe Basin. From 2006 to 2008, 442 square plots (0.1 ha) were established and surveyed throughout the Lake Tahoe Basin, including 176 control plots > 300 m from roads, and 137 plots originally established in 1990 that were used for long-term trends. Both incidence and severity of salt damage, diseases, insect pests, and other abiotic damage were recorded on all trees within plots (more than 10,000 trees). Soil and vegetation samples were collected from a subset of plots and analyzed for salt content. At least 15% of roadside trees were damaged by salt every year. Very large year-to-year variation in the incidence of salt damage was observed, but the severity of salt damage has decreased since 1990. A clear roadside effect on roadside conifers existed because symptoms of salt damage were only observed on trees in roadside plots and never in control plots, and foliage from trees in roadside plots had more sodium and chloride content than those in control plots for both salt symptomatic and asymptomatic foliage. Incidence of salt damage decreased with increasing distance from roads, was more frequent on rocky soils, and increased with downhill slope steepness and tree density. Pines ( Pinus spp.) were more frequently and severely damaged by salt than firs ( Abies spp.). Trees were more likely to be damaged by something other than salt, and the relationship among salt damage and other damages was antagonistic rather than synergistic. The results from this study have important implications for the ecology and management of conifer forests in relation to salinity and road maintenance.