Effect Of Surface Slope Research Articles

Unified Topographic and Atmospheric Correction for Remote Imaging Spectroscopy

Models linking surface characteristics within incident solar radiation are inexorably dependent on the topography of the given region. To date, however, most operational surface reflectance retrievals treat this dependence by assuming a flat terrain, leading to significant deviations in the estimated reflectance. Here, we demonstrate that incorporating dynamic topography directly into the joint surface and atmospheric model during retrievals has several advantages. First, it allows for a more complete physical accounting of downwelling illumination, providing more accurate estimates of the absolute magnitude of reflectance. Second, it facilitates a superior resolution of the atmospheric state, most notably due to the confounding influence of atmospheric aerosols and unresolved topographic effects. Our methodology utilizes a practical, high-fidelity, model-driven approach to separate out diffuse and direct irradiation and account for topographic effects during the joint inversion of atmosphere and surface properties. We achieve this by enhancing the atmosphere/surface inversion to account for the radiative transfer effects of surface slope. We further demonstrate how uncertainties in topographic features can be quantified and leveraged within our formulation for a more realistic posterior uncertainty estimates. Our results demonstrate that the inclusion of topographic effects into the retrieval model reduces errors in the reflectance of an only moderately rugged terrain by more than 15%, and that a post hoc accounting of topography cannot achieve these same results.

A single surface slope effects on seismic response based on shaking table test and numerical simulation

This paper presents the effects of a single surface slope on seismic ground responses and exhibits the peak horizontal acceleration (PGAh) distribution regulations in the slope cross-section under vertically impinging SV wave excitation. The seismic response of a homogeneous slope was investigated through a series of shaking table tests, and physical modelling was used to verify the numerical simulation. Subsequently, many numerical simulations were conducted considering slope geometry and input ground motion using Fast Lagrangian Analysis of Continua in Three Dimensions (FLAC3D). Two patterns of PGAh distribution are summarised for single surface slopes: one type is the low slope dynamic response, which shows that PGAh increases along the slope surface with the increase in the slope elevation, varies little with the increase in the distance from the slope surface to the inside in the horizontal direction. The other type is the high slope dynamic response, which shows that PGAh changes periodically and takes on a certain pattern along the slope surface with the increase in the slope elevation, and decreases gradually with the increase in the distance from the slope surface to the inside in the horizontal direction. Meanwhile, the critical height of the slope for different distribution patterns of PGAh varies with the slope material and the harder the rock material, the higher the critical slope height for the distribution patterns of PGAh. The critical height of Hcr which is approximately 0.17–0.20 times the incident wavelength (λ), divides the two types of dynamic response of the slope based on the dimensional analysis method and numerical simulations. That is, the chart of its dynamic response will have a high dynamic response when the slope height is greater than Hcr, and its dynamic response will present as a low slope dynamic response when the slope height is less than Hcr. The amplification coefficient at the crest increases with an increase in the dimensionless slope height (H/λ) and reaches the first peak value when H/λ reaches 0.17–0.20. The de-amplification at the crest occurred when H/λ was >0.4. The novel findings can support the input ground motion parameters for earthquake slope engineering design.

Walking on Mild Slopes and Altering Arm Swing Each Induce Specific Strategies in Healthy Young Adults.

Slopes are present in everyday environments and require specific postural strategies for successful navigation; different arm strategies may be used to manage external perturbations while walking. It has yet to be determined what impact arm swing has on postural strategies and gait stability during sloped walking. We investigated the potentially interacting effects of surface slope and arm motion on gait stability and postural strategies in healthy young adults. We tested 15 healthy adults, using the CAREN-Extended system to simulate a rolling-hills environment which imparted both incline (uphill) and decline (downhill) slopes (± 3°). This protocol was completed under three imposed arm swing conditions: held, normal, active. Spatiotemporal gait parameters, mediolateral margin of stability, and postural kinematics in anteroposterior (AP), mediolateral (ML), and vertical (VT) directions were assessed. Main effects of conditions and interactions were evaluated by 2-way repeated measures analysis of variance. Our results showed no interactions between arm swing and slope; however, we found main effects of arm swing and main effects of slope. As expected, uphill and downhill sections of the rolling-hills yielded opposite stepping and postural strategies compared to level walking, and active and held arm swings led to opposite postural strategies compared to normal arm swing. Arm swing effects were consistent across slope conditions. Walking with arms held decreased gait speed, indicating a level of caution, but maintained stability comparable to that of walking with normal arm swing. Active arm swing increased both step width variability and ML-MoS during downhill sections. Alternately, ML-MoS was larger with increased step width and double support time during uphill sections compared to level, which demonstrates that distinct base of support strategies are used to manage arm swing compared to slope. The variability of the rolling-hills also required proactive base of support changes despite the mild slopes to maintain balance.

Direct numerical simulation on the effects of surface slope and skewness on rough-wall turbulence

This paper presents direct numerical simulation results of turbulent flows over systematically varied rough surfaces. Three-dimensional irregular rough surfaces with varying effective slope and skewness factor and fixed roughness height scales were considered in the study. The skewness factor characterizes whether the surface of interest has a peak-dominated or valley-dominated nature, whereas the effective slope measures the wavelength of the surface undulations or solidity of the roughness elements. The influence of these two topological parameters on the friction drag at rough surfaces was investigated. Downward shifts in the inner-scaled mean velocity, which quantify an increase in the friction drag, were found to be larger for surfaces with a positive skewness factor, and this trend was found to be more pronounced as the effective slope increased. In addition, the downward shift value steeply increased with increases in the effective slope, while the dependence weakened when the effective slope was larger than a certain threshold value. The physical mechanism behind the increase in the roughness function was investigated by analyzing the momentum budgets. It was revealed that the viscous drag dominantly contributes to the roughness function when the effective slope value is small, whereas the contribution by the pressure drag progressively increases with the effective slope. We also found that for surfaces with larger effective slope consisting of relatively shorter wavelength undulations, the Reynolds shear stress tends to be reduced because the wall roughness prevents the formation of quasi-streamwise elongated vortices suppressing the turbulent near-wall cycles. This acts as a negative contribution to the roughness function, and the two competing effects (of the increase in pressure drag and decrease in Reynolds shear stress) weaken the dependence of the effective slope value on the roughness function. Further analysis was conducted to better understand how the surface slope and skewness factor values affect the mean flow field, modifying the pressure and viscous drag forces.

Do Surface Slope and Posture Influence Lower Extremity Joint Kinetics during Cycling?

The purpose of this study was to investigate the effects of surface slope and body posture (i.e., seated and standing) on lower extremity joint kinetics during cycling. Fourteen participants cycled at 250 watts power in three cycling conditions: level seated, uphill seated and uphill standing at a 14% slope. A motion analysis system and custom instrumented pedal were used to collect the data of fifteen consecutive cycles of kinematics and pedal reaction force. One crank cycle was equally divided into four phases (90° for each phase). A two-factor repeated measures MANOVA was used to examine the effects of the slope and posture on the selected variables. Results showed that both slope and posture influenced joint moments and mechanical work in the hip, knee and ankle joints (p < 0.05). Specifically, the relative contribution of the knee joint to the total mechanical work increased when the body posture changed from a seated position to a standing position. In conclusion, both surface slope and body posture significantly influenced the lower extremity joint kinetics during cycling. Besides the hip joint, the knee joint also played the role as the power source during uphill standing cycling in the early downstroke phase. Therefore, adopting a standing posture for more power output during uphill cycling is recommended, but not for long periods, in view of the risk of knee injury.

Evaluation of the Effects of Surface Slope in Discretization of Groundwater Models

A robust representation of hydrogeological properties of the examined study area in discretization step is essential in groundwater modelling to improve the accuracy and efficiency of the model. A number of studies have investigated the effect of grid cell size in model discretization using comparison of performances of different models representing different cell sizes. However, although grid size refinement effect on model performances was calculated, the impact of mean slope was not conclusively discussed. In this study, five models distinguished by five spatial discretization schemes; 10 x 10 m, 20 x 20 m, 30 x 30 m, 40 x 40 m and 50 x 50 m were constructed. Using PEST, hydraulic conductivity and specific yield values over a selection of pilot points were estimated. The effect of surface slope is discussed in order to recommend the most appropriate location for observation well placement in terms of topographical characteristic. It is confirmed that the deterioration of model performance is controlled by mean slope of the surface. Results reveal that model performance increases substantially for areas of low slope (< 3 %) and medium slope (3 ~ 10 %) for smaller a grid cell size. Therefore, to improve model performance, it is recommended that the observations wells are placed in areas of low and medium slopes.

Effect of surface slope and build orientation on surface finish and dimensional accuracy in material jetting processes

This work seeks to elucidate the effect of surface slope and build orientation upon the surface finish and dimensional accuracy of specimens fabricated by material jetting processes. Specimens with a flat area and four feature designs (i.e., spherical and prismatic hole and protrusions) were printed in two orientations (i.e., along (XY) and across (YX) the print head direction) and two surface slopes (i.e., horizontal (0∘) and 45∘) and scanned with a white-light profilometer to quantify the surface texture, areal, and material ratio parameters for dimensional accuracy and areal fidelity. The results indicate that surface slope and build orientation appear to have a greater influence on the recessed features compared to the protruded ones. The height and volumetric functional surface parameters are significant and show better surface finish for the 0∘ surface slope compared to 45∘. Also, prismatic and recessed features might benefit from printing on a 45∘ sloped surface while the design fidelity of cross-sections in holes and protrusions greatly vary depending on the specimen slope. The contributions of this work include illustrating the potential for increased production, resolution and fidelity capabilities if 3D printing equipment could incorporate tilting print trays, adaptable print orientation, and local angles, among others.

Surface slope effects for ripple orientation on sand dunes in López crater, Terra Tyrrhena region of Mars

Abstract Ripple orientations on small sand dunes (dunes lacking substantial slip faces) at widely distributed sites across Mars have been documented using High Resolution Imaging Science Experiment (HiRISE) images, in an effort to determine the last formative aeolian sediment transport direction experienced at these locations. Howard (1977) used field measurements and first principles to derive an expression for determining how much the surface slope on a sand dune deflects the orientation of sand ripples with respect to the formative wind direction. A Digital Terrain Model derived from stereo HiRISE images was used to assess the potential deflection of ripples on sand dunes on the floor of Lopez crater on Mars. Three-quarters of the area covered by sand dunes within the DTM has a surface slope

Comprehensive quantitative investigation of arm swing during walking at various speed and surface slope conditions

Previous studies have shown that inclusion of arm swing in gait rehabilitation leads to more effective walking recovery in patients with walking impairments. However, little is known about the correct arm-swing trajectories to be used in gait rehabilitation given the fact that changes in walking conditions affect arm-swing patterns. In this paper we present a comprehensive look at the effects of a variety of conditions on arm-swing patterns during walking. The results describe the effects of surface slope, walking speed, and physical characteristics on arm-swing patterns in healthy individuals. We propose data-driven mathematical models to describe arm-swing trajectories. Thirty individuals (fifteen females and fifteen males) with a wide range of height (1.58–1.91m) and body mass (49–98kg), participated in our study. Based on their self-selected walking speed, each participant performed walking trials with four speeds on five surface slopes while their whole-body kinematics were recorded. Statistical analysis showed that walking speed, surface slope, and height were the major factors influencing arm swing during locomotion. The results demonstrate that data-driven models can successfully describe arm-swing trajectories for normal gait under varying walking conditions. The findings also provide insight into the behavior of the elbow during walking.

Determination of Local Slope on the Greenland Ice Sheet Using a Multibeam Photon-Counting Lidar in Preparation for the ICESat-2 Mission

The greatest changes in elevation in Greenland and Antarctica are happening along the margins of the ice sheets where the surface frequently has significant slopes. For this reason, the upcoming Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) mission utilizes pairs of laser altimeter beams that are perpendicular to the flight direction in order to extract slope information in addition to elevation. The Multiple Altimeter Beam Experimental Lidar (MABEL) is a high-altitude airborne laser altimeter designed as a simulator for ICESat-2. The MABEL design uses multiple beams at fixed angles and allows for local slope determination. Here, we present local slopes as determined by MABEL and compare them to those determined by the Airborne Topographic Mapper (ATM) over the same flight lines in Greenland. We make these comparisons with consideration for the planned ICESat-2 beam geometry. Results indicate that the mean slope residuals between MABEL and ATM remain small ( 0.05 °) through a wide range of localized slopes using ICESat-2 beam geometry. Furthermore, when MABEL data are subsampled by a factor of 4 to mimic the planned ICESat-2 transmit-energy configuration, the results are indistinguishable from the full-data-rate analysis. Results from MABEL suggest that ICESat-2 beam geometry and transmit-energy configuration are appropriate for the determination of slope on ~ 90-m spatial scales, a measurement that will be fundamental to deconvolving the effects of surface slope from the ice-sheet surface change derived from ICESat-2.

A GIS-ANN-Based Approach for Enhancing the Effect of Slope in the Modified Green-Ampt Model

Most infiltration models survey infiltration in large scale regions using an assumption that the slope of the ground is equal to zero. The Modified Green and Ampt model is one of a few infiltration models that considers slope as an input parameter in its formulation. Here, using artificial neural networks in a raster-based design, basic research is presented regarding the effect of surface slope on infiltration. For the investigation, three catchments with different areas and slopes were selected as case studies, based on existing runoff stations in the upstream region of the Johor River Basin in southern Malaysia. In this research, the efficiency of six different functions was studied in order to determine the best performer for slope in the Modified Green and Ampt model. We also sought to find the most suitable ANN transfer function for infiltration calculations. By calculating runoff for each pixel, accumulation maps were used for corroborating the suitability of the obtained results. The results indicated that the Log-sigmoid was the most appropriate transfer function. We also determined that using the exponential form for the slope in the Modified Green and Ampt model formulation was more accurate, as compared to the original linear shape.

Predicting aeolian sand transport rates: A reevaluation of models

Abstract Eight aeolian sand-transport models are evaluated using a field data set and a new approach to estimating shear velocity. The models are those of Bagnold, 1937 , Kawamura, 1951 , Zingg, 1953 , Owen, 1964 , Kadib, 1965 , Hsu, 1971 , Lettau and Lettau, 1978 , Sorensen, 2004 . All of these models predict transport as a function of shear velocity to the third power. Shear velocities are estimated using wind profile data (log-linear slope) with the von Karman constant and with the apparent von Karman parameter and the results of the different approaches are evaluated based on comparison of regression statistics and RMS error. The models were not adjusted to account for sediment moisture content or local surface slope effects. All of the models have about the same statistical explanatory power, so evaluations were made by comparing slopes and intercepts of best fit (least-squares) lines and RMSE. From this basis, we conclude that predictions made with the Bagnold (1937) model best match our observations, with the models of Kadib, 1965 , Hsu, 1971 performing nearly as well. The Lettau and Lettau, 1978 , Kawamura, 1951 model predictions match observations least.

The effects of surface slope on multi-segment foot kinematics in healthy adults

Previous work evaluating the effects of surface slope on gait has focused on lower extremity kinematics and kinetics. However, an assessment of multi-segment foot kinematics during walking on inclined and declined ramps has not been previously reported. Sagittal ankle motion using a single rigid body foot model and three-dimensional hindfoot and forefoot kinematics for 24 healthy adults (16 females and 8 males, average age 25.5 ± 4.4 years) were compared during level surface, inclined surfaces of 3%, 6%, 9% and 12% grade and a declined surface of approximately 7.5% grade at a constant speed using a standard treadmill. Significant differences in peak hindfoot plantarflexion, sagittal plane range of motion and time of peak dorsiflexion, plantarflexion, varus and valgus were seen between surface slope conditions. Significant changes were also seen in forefoot plantarflexion and sagittal plane range of motion however the maximum difference between conditions was less than 3°. These results indicate that foot mechanics can be significantly altered when ambulating on ramps in healthy adults. Specifically, treadmill protocols which incorporate different surface slopes often encountered during ambulation of daily living, may provide an improved technique in evaluating a patient's ability to function in the community.

From divots to swales: Hillslope sediment transport across divers length scales

In soil‐mantled steeplands, soil motions associated with creep, ravel, rain splash, soil slips, tree throw, and rodent activity are patchy and intermittent and involve widely varying travel distances. To describe the collective effect of these motions, we formulate a nonlocal expression for the soil flux. This probabilistic formulation involves upslope and downslope convolutions of land surface geometry to characterize motions in both directions, notably accommodating the bidirectional dispersal of material on gentle slopes as well as mostly downslope dispersal on steeper slopes, and it distinguishes between the mobilization of soil material and the effect of surface slope in giving a downslope bias to the dispersal of mobilized material. The formulation separates dispersal associated with intermittent surface motions from the slower bulk behavior associated with small‐scale bioturbation and similar dilational processes operating mostly within the soil column. With a uniform rate of mobilization of soil material, the nearly parabolic form of a hillslope profile at steady state resembles a diffusive behavior. With a slope‐dependent rate of mobilization, the steady state hillslope profile takes on a nonparabolic form where land surface elevation varies with downslope distance x as xa with a ∼ 3/2, consistent with field observations and where the flux increases nonlinearly with increasing slope. The convolution description of the soil flux, when substituted into a suitable expression of conservation, yields a nonlinear Fokker‐Planck equation and can be mapped to discrete particle models of hillslope behavior and descriptions of soil‐grain transport by rain splash as a stochastic advection‐dispersion process.

Surface slope effects on shingling frequency and postural balance in a simulated roofing task

The purpose of this study was to investigate the influence of surface slopes (18°, 26°, 34°) on the maximum acceptable roof shingling frequency for males performing a simulated roof-shingling task. The psychophysical roof shingling frequency was also compared to the postural sway and trunk motion values. The maximum acceptable roof shingling frequency and selected trunk motion decreased significantly with an increase in slope. Postural sway however increased significantly with an increase in slope. The study also revealed that workers were experiencing a greater postural sway at the earlier phase of task on the steeper surface. This suggests that there might be an adaptation period associated with working on a slope and the body's ability to compensate for a loss of balance. Therefore, more emphasis should be given to the workers in this adaptation period, with additional monitoring and cautionary measures. Collectively, the findings of the study could be utilized for improving work practices on roofs, while reducing the potential risks of falls in roofing construction.

Backpack load positioning and walking surface slope effects on physiological responses in infantry soldiers

The primary purpose of this study was to survey a sample of infantry soldiers to determine their preferred backpack load distribution. The second objective was to examine the effect of backpack load position, walking speed and surface grade on the physiological responses of infantry soldiers. In the first phase of the study, analysis of 500 questionnaires indicated that backpack item arrangement was typically determined by convenience and habit. About 33.6% and 30.6% of the soldiers reported placing heavier items in the lower and higher positions, respectively. In the second experimental phase of the study, five male infantry soldiers who had completed basic training (including 30 km tactical road march) each performed eight treadmill walking bouts at one of two speeds (i.e., 3.2 and 6.4 km/h) and two surface grades (0% and 6%) carrying 15% of their body weight in a backpack with two chambers (upper and lower). Respiratory frequency, minute ventilation, oxygen consumption and heart rate were recorded using the Quark pulmonary system. The MANOVA results indicate that the effect of walking speed was strongly significant for all physiological indices. In addition, as might be expected, walking on a 6% grade was associated with higher oxygen consumption and heart rate compared to level going. In terms of load position, the mean respiratory frequency was significantly higher where the load was carried in the upper position. Furthermore, there was a significant interaction between load position and walking grade on oxygen consumption. Where participants were walking at zero incline, there was no significant difference in mean oxygen consumption. By contrast, the mean oxygen consumption was significantly higher where loads were carried in the upper position and negotiating the 6% grade. Previous research has found that, ideally, load carriage should complement stability, bringing the load's center of gravity as close to the body as possible and making use of the larger muscles. However, carrying heavy loads close to the trunk can affect lung function. Thus, load placement is an important factor in physiological response to load carriage, and optimum choice of upper or lower position when distributing items in a backpack may be dependent on the walking grade. Relevance to industry The need to carry heavy loads for long distances is common to a range of human endeavor, with physical transport used by soldiers, various types of workers and recreational hikers. Load distribution and walking gradient are important factors in terms of the efficiency of load carriage and should be taken into consideration in both the design and loading of backpacks. Thus, the findings of the present study will be relevant to infantry soldiers, mountain climbers or of manual material handling (MMH) in industry, providing practical implications for tasks associated with exposure to uneven walking/working surfaces.

Spatial and temporal variations in albedo on Storglaciären, Sweden

AbstractExtensive albedo data from Storglaciären, Sweden, during nine summers are analyzed, focusing on the effect of surface slope on measurements and on the influence of clouds on albedo of both snow and ice surfaces. On clear-sky days, albedo continuously dropped throughout the day by &gt; 0.3 when derived from measurements in a horizontal plane over the slightly sloping surface. When we correct for the tilt effect, over frozen surfaces the apparent decrease in albedo largely disappeared, while over melting surfaces it became significantly less pronounced. This emphasizes the need to correct horizontally measured data for slope when they are used, for example, as ground truth for satellite-derived albedo, or in high-resolution glacier melt runoff models. Albedo varied by &gt; 0.1 due to cloud fluctuations. To quantify cloud effects, albedo changes between successive (half-)hourly and daily data were regressed against corresponding changes in cloudiness expressed by the ratio of global radiation to top-of-atmosphere solar radiation. The resulting relationship over snow explains 66% of oberved albedo changes using hourly, and 42% using daily, time-steps. Over ice, the corresponding values are 28% and 0%. Hence, cloudiness is a dominating factor in determining short-term variability of albedo over snow, whereas over ice the observed large day-to-day variability ( &gt; 20%) is mainly attributed to changes in the physical characteristics of the weathering crust. Results suggest that cloud effects should be incorporated into models treating snow and ice surfaces separately.

Sensitivity of surface heat and moisture fluxes due to topographic slope and azimuth

Current surface vegetation atmospheric transfer (SVAT) models neglect the effects of surface slope and azimuth. There are significant subgrid differences in topographic features at the subgrid scales to which processes such as latent and sensible heating fluxes are sensitive. This study indicates the sensitivity of these processes due to sloping surfaces of varying azimuth (clockwise horizontal direction from north). A dynamically adaptive gridding system is implemented to determine subgrids based on surface slope and azimuth. A topographic index which accounts for four surface azimuth and five slope increments defines 21 characteristic types, including flat horizontal surfaces. A synthetic 10 km×10 km watershed at latitude 38°N and with a fixed diurnal cycle provides input for the surface temperature. Two fine grid meshes, 1.0 km×1.0 km and 2 km×2 km, are embedded within the larger‐scale cell. Digital elevation data representing an area near Lake Tahoe, California, is also used in this sensitivity study of surface heat and moisture fluxes due to topographic forcing of incident radiation. A homogeneity test determines the minimum number of fine scale cells with matching characteristics and shared boundaries (but not strictly shared points) and forms groups of cells which represent regions of similar topographic characteristics. When the homogeneity test is set to 100% accuracy, there is a 72% reduction from individual fine grid cells to similar groups, while at 60% accuracy there is an 80% reduction, and at 10% accuracy there is a 99% reduction. Each group computes a SVAT with the group defined characteristic topography. A set of test cases using the Biosphere‐Atmosphere Transfer Scheme (Dickinson et al., 1986) is presented for north, south, east, and west facing 10° slopes with surfaces under dry and saturated conditions. The resulting latent heat fluxes are shown for grasslands and evergreen forests under dry and saturated conditions and for the synthetic watershed at varying degrees of accuracy. The Sierra topography is assumed to be all evergreen vegetation and dry. This study indicates that flat horizontal surfaces overpredict diurnally integrated, areally weighted sensible heat fluxes by 5 to 10% and latent heat fluxes by 1 to 2%.

The effect of surface slope on saltation threshold

ABSTRACTA new wind tunnel has been constructed to study the mass transport properties of wind‐blown sand. This report on the first set of experiments in the new wind tunnel concerns the effect of slope on threshold friction speed. The results of this series of static threshold experiments (and one dynamic threshold experiment) for a range of particle diameters and bed slope angles show that, provided the effects of Reynolds number variation and interparticle cohesive force are accounted for, the static friction angle α is independent of slope and close in value to the measured static angle of response.

Rain impact soil crust. II. Some effects of surface slope, drop size and soil variation

Formation and non-formation of the rain-impact soil crust were studied experimentally over ranges of surface-slope, drop-size and soil variation. In these contexts, the formative process was found to be very versatile. However, stable particles, of a size just movable on the soil surfaces by raindrops, appear to play a special role in preventing crust development. Becoming juxtaposed on the surface, these particles form clusters which allow hydraulic penetration of water from impacting drops, through their large pores. This maintains loose packing in the near-surface zone as opposed to the compaction associated with crust formation where only small surface pores exist. A method of soil modification, involving increasing the proportion of durable, barely rain-movable particles in soils, is suggested as a means of combating crusting on a long-term basis.