Response Time of Forested Mountainous Watersheds in Humid Regions

2000 ◽  
Vol 31 (3) ◽  
pp. 149-168 ◽  
Author(s):  
A. Loukas ◽  
N. R. Dalezios
Keyword(s):  
Field Experiments ◽  
Time Lag ◽  
Wave Theory ◽  
Roughness Coefficient ◽  
Stream Channel ◽  
Stream Channels ◽  
Mountainous Watersheds ◽  
Two Phases ◽  
Comparison Of The Results ◽  
Estimation Of Time

This study proposes an analytical method for the estimation of time lag for forested mountainous watersheds. The water flow in a watershed is separated and analyzed in two phases, the land or hillslope phase and the stream channel phase. In many areas around the globe the flow in a forested high gradient watershed is generated through subsurface pathways as several field experiments have shown. The kinematic wave theory is used to describe the generation of flow from steep forested hillslopes. This hillslope runoff is, then, used as input to the stream channels. The equations were developed by assuming kinematic conditions in the stream channel and that the stream slope and the roughness coefficient i) vary according to a second order polynomial with the distance from the mouth of the watershed, ii) vary linearly with the distance from the outlet of the watershed, and iii) are constant throughout the watershed. Comparison of the results of the proposed equation with data from two experimental watersheds in Coastal British Columbia indicates that the three expressions of the proposed equation, even the simplest one assuming constant stream slope and roughness coefficient, are reliable and give good approximation of the observed time lag.

A mediation model of leaders’ favoritism

2018 ◽  
Vol 47 (7) ◽  
pp. 1330-1344
Author(s):  
Man-Ling Chang ◽  
Cheng-Feng Cheng
Keyword(s):  
Hierarchical Linear Modeling ◽  
Time Lag ◽  
Mediation Model ◽  
Linear Modeling ◽  
Content Type ◽  
Justice Perception ◽  
Lmx Theory ◽  
Member Exchange ◽  
Nested Structure ◽  
Two Phases

PurposeThe purpose of this paper is to develop a mediation model for understanding how favoritism, in the context of the leader–member exchange (LMX) theory, influences subordinate-rated LMX via the subordinates’ perception of organizational justice.Design/methodology/approachThe sample comprised 39 managers and 159 employees working in local branches of banks in Taiwan. While the managers were asked to rate their LMX scores with all employees, three to five employees were randomly selected to participate in a survey which included two phases with a time lag of three months. Given the nested structure of the data, hierarchical linear modeling was used to examine the mediation model.FindingsThe findings support the mediation model, indicating that LMX favoritism can significantly influence subordinate-rated LMX by enhancing subordinates’ justice perception.Originality/valueThe study contributes to the existing LMX research by showing that a superior’s LMX favoritism may change subordinate-rated LMX over time.

scholarly journals Bankfull discharge estimation for Fishpot Creek

2020 ◽  
Vol 2 (5) ◽  
pp. 74-91
Author(s):  
Farhad Sakhaee
Keyword(s):  
Laser Scanning ◽  
Roughness Coefficient ◽  
3D Laser Scanning ◽  
Stream Channel ◽  
Cross Sectional ◽  
Bankfull Discharge ◽  
Data Points ◽  
The Cross ◽  
Sectional Shape ◽  
Discharge Estimation

Abstract: Fishpot Creek has been investigated and bankfull discharge was calculated based on the collected data points obtained from 3D laser scanning of the stream. This report consists of two major parts. One is the 3D scanning and analysis the results, other part includes sampling of both bed and bank materials. In the first part, essential parameters of roughness coefficient based on Cowan’s method were calculated as well as calculating the cross-sectional area and wetted perimeter based on the profile obtained from stream channel scanning.  Leica Scan Station HDS 3000 scanner was used to visualize the cross-sectional shape of the stream based on a high-density scan technology and finally applied to the manning’s equation to calculate the bankfull discharge. for sampling part both bed and bank materials were analyzed in lab, mechanical sieve test performed to investigate the gradation of bed and banks materials within the study area.

THE CRITICAL OPALESCENCE OF ETHYLENE

1948 ◽  
Vol 26b (8) ◽  
pp. 592-603
Author(s):  
O. Maass ◽  
S. G. Mason
Keyword(s):  
Oleic Acid ◽  
Critical Temperature ◽  
Time Lag ◽  
The Other ◽  
Statistical Fluctuations ◽  
Maximum Value ◽  
Critical Opalescence ◽  
Phase Discontinuity ◽  
Two Phases ◽  
Smoluchowski Theory

The opalescence of ethylene has been investigated under various conditions in the region of the critical temperature. The opalescence of critical fillings increases as the temperature is lowered and passes through a maximum at the critical dispersion temperature Ts. When the system is heated the value depends upon the thermal history, both below and above Ts. Two types of time lag curve are observed in the irreversible region, one in which the opalescence passes through a minimum and then a maximum value, and the other through a minimum only. It is believed on the basis of previous qualitative studies that violent shaking would result in reversibility with respect to changes in temperature. Once the apparent phase discontinuity has disappeared the opalescence becomes reversible as long as condensation is prevented. The opalescence of critical fillings depends upon the density and appears to be a maximum when the two phases are present in equal volumes at Ts. Air and oleic acid present in small quantities depress Ts but do not appear to change the variation of opalescence with (T − Ts) when T > Ts. These observations appear to disagree with the classical Einstein–Smoluchowski theory based on light scattering resulting from statistical fluctuations in density. This theory predicts a maximum opalescence at the classical critical temperature, which in the case of ethylene is 0.7 °C. higher than Ts. If, however, the more recent views of the nature of the P − V isotherms near the critical point are taken into account, some of the conflict disappears.

Computational and experimental study of the stress state of the connecting rod of the opposed compressor to assess the probability of failure-free operation

2020 ◽  
Vol 86 (5) ◽  
pp. 52-58
Author(s):  
I. M. Petrova ◽  
M. A. Filimonov
Keyword(s):  
Experimental Data ◽  
Experimental Study ◽  
Stress State ◽  
Numerical Experiment ◽  
Field Experiments ◽  
Fatigue Cracks ◽  
Tangential Force ◽  
Experimental Studies ◽  
Connecting Rod ◽  
Comparison Of The Results

Fatigue cracks in the piston heads of the connecting rods of opposed compressors can occasionally develop in service. A study of the loading of the connecting rods of the compressors operating in chemical production was carried out to assess the probability of their failure-free operation. Since the experimental study of stresses acting in large structural elements is rather difficult, the study of the stress state was carried out using computational methods with subsequent comparison of the results with the experimental data. When loading the connecting rod, there is an area affected by the distributed load and another area with a gap between the cylindrical surfaces where the contact pressure is absent. The forces acting on the boundary of the contact areas and the gap of the finger with the connecting rod bore are determined: the radial force N, tangential force Q and bending moment M. N and Q are considered functions of the contact angle α. Using numerical experiments, we determined the stresses in the zone from the angle α corresponding to the end of the contact zone to the angle of transition of the head in the shank of connecting rod in conditions of varied operational loads and gaps in the connecting rod — finger coupling. The values and character of changes in the loads affecting the crank mechanism of the compressor during operation are determined experimentally. The distribution of stresses in the sections of the connecting rod and the most loaded cross-sections are specified. the results of the numerical experiment are compared with the experimental data. Comparison of the results of numerical and field experiments has shown that the numerical experiment provides the similar assessment of the stress distribution, moreover, the numerical experiment allows us to estimate the simultaneous effect of both loads and gaps on the stress growth which is almost impossible to be determined by experimental studies.

A natural approach to watershed planning, restoration and management

1999 ◽  
Vol 39 (12) ◽  
pp. 347-352 ◽  
Author(s):  
Mark M. Petersen
Keyword(s):  
Planning Process ◽  
Alluvial Fans ◽  
Watershed Restoration ◽  
Stream Channel ◽  
Stream Channels ◽  
Alluvial Valley ◽  
Field Approach ◽  
Natural Approach ◽  
Ecological Principles ◽  
Potential Component

Each watershed has an overall hydrologic function to capture, store and safely release water. How well a watershed is able to perform this overall function is dependent upon how well each geomorphic component landform is functioning within the watershed. Each geomorphic component landform within a watershed has a specific hydrologic function and ecological potential. Component landforms that commonly occur in a watershed include stream channels, floodplains, stream terraces, alluvial valley bottoms, alluvial fans, mountain slopes, and ridge tops. When a component landform within a watershed becomes ecologically altered or degraded, its ability to perform its natural hydrologic and geomorphic functions becomes impaired and the watershed or ecosystem is unable to function properly. Component landforms within a watershed are interrelated. For example, the condition of a stream channel is closely related to the condition of its floodplain. Water from upland slopes is transported over and through alluvial fans and bottoms. Therefore, each component landform needs to be considered in the planning process and in setting watershed goals. This paper presents a simple field approach to inventory, evaluate and plan watershed restoration based on geomorphic, hydrologic and ecological principles. Examples of successful use of the approach on several watersheds in Utah, USA are given.

scholarly journals Evaluation of the Dropsonde Humidity Sensor Using Data from DYCOMS-II and IHOP_2002

2005 ◽  
Vol 22 (3) ◽  
pp. 247-257 ◽  
Author(s):  
Junhong Wang
Keyword(s):  
Humidity Sensor ◽  
Field Experiments ◽  
Large Time ◽  
Time Lag ◽  
Measured Temperature ◽  
Marine Stratocumulus ◽  
Stratocumulus Clouds ◽  
The Mean ◽  
Using Data ◽  
Dry Bias

Abstract The dropsonde humidity data have not been fully utilized due to lack of knowledge on performance of the dropsonde humidity sensor. This study evaluates the performance of the dropsonde humidity sensor using data collected from two field experiments, the Dynamics and Chemistry of Marine Stratocumulus Phase II: Entrainment Studies (DYCOMS-II) and the International H2O Project (IHOP)_2002. During DYCOMS-II, 63 dropsondes were dropped above marine stratocumulus clouds. It provides a unique opportunity to evaluate the performance of the dropsonde humidity sensor within clouds. Relative humidity (RH) inside clouds did not reach 100% all the time, but the maximum RH reached 100% for 28% of soundings and was within the sensor accuracy range (94%–100%). This suggests that the dropsonde humidity sensor displays no systematic dry bias near saturation. The dropsonde humidity sensor experienced large time-lag errors when it descended from a dry environment above clouds into clouds. The mean estimated time constant of the sensor is 5 s at 15°C, which is much larger than 0.5 s at 20°C given by the manufacturer. The humidity sensor still reported near-saturation RH after it exited clouds because of water on the sensor. The approximately coincident dropsonde and aircraft temperature data during DYCOMS-II show that the dropsonde underestimates temperatures inside and below clouds by averages of 0.21° and 0.93°C, respectively. Seventy-one pairs of dropsonde and radiosonde soundings during IHOP_2002 were launched within a half hour and 50 km and sampled the same air mass based on the visual examination. The comparisons show that the dropsonde and radiosonde RH data agree with each other within ±2% RH, suggesting no systematic dry bias in dropsonde humidity data. However, dropsonde-measured temperature is consistently colder than that by radiosonde by ∼0.4°C.

Models of Invasion and Establishment for African Mustard (Brassica tournefortii)

2014 ◽  
Vol 7 (4) ◽  
pp. 599-616 ◽  
Author(s):  
Kristin H. Berry ◽  
Timothy A. Gowan ◽  
David M. Miller ◽  
Matthew L. Brooks
Keyword(s):  
Sonoran Desert ◽  
Ecosystem Change ◽  
Data Sets ◽  
Annual Plants ◽  
Stream Channel ◽  
Stream Channels ◽  
Ephemeral Stream ◽  
Disturbed Areas ◽  
Brassica Tournefortii ◽  
Noxious Weed

AbstractIntroduced exotic plants can drive ecosystem change. We studied invasion and establishment ofBrassica tournefortii(African mustard), a noxious weed, in the Chemehuevi Valley, western Sonoran Desert, California. We used long-term data sets of photographs, transects for biomass of annual plants, and densities of African mustard collected at irregular intervals between 1979 and 2009. We suggest that African mustard may have been present in low numbers along the main route of travel, a highway, in the late 1970s; invaded the valley along a major axial valley ephemeral stream channel and the highway; and by 2009, colonized 22 km into the eastern part of the valley. We developed predictive models for invasibility and establishment of African mustard. Both during the initial invasion and after establishment, significant predictor variables of African mustard densities were surficial geology, proximity to the highway and axial valley ephemeral stream channel, and number of small ephemeral stream channels. The axial valley ephemeral stream channel was the most vulnerable of the variables to invasions. Overall, African mustard rapidly colonized and quickly became established in naturally disturbed areas, such as stream channels, where geological surfaces were young and soils were weakly developed. Older geological surfaces (e.g., desert pavements with soils 140,000 to 300,000 years old) were less vulnerable. Microhabitats also influenced densities of African mustard, with densities higher under shrubs than in the interspaces. As African mustard became established, the proportional biomass of native winter annual plants declined. Early control is important because African mustard can colonize and become well established across a valley in 20 yr.

scholarly journals Finite Element Analysis of the Effect of Currents on the Dynamics of a Moored Flexible Cylindrical Net Cage

2021 ◽  
Vol 9 (2) ◽  
pp. 159
Author(s):  
Zhongchi Liu ◽  
Sarat Chandra Mohapatra ◽  
C. Guedes Soares
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Numerical Model ◽  
Analytical Model ◽  
Structural Response ◽  
Wave Theory ◽  
Design Parameters ◽  
Element Analysis ◽  
Net Cage ◽  
Comparison Of The Results

A numerical model associated with wave–current interactions with a moored flexible cylindrical cage was developed based on the finite element method. An analytical model was formulated under the linearised wave theory and small structural response, and a semi-analytical solution was obtained using the Fourier Bessel series solution and least squares approximation method, along with a matching technique. The numerical results from the finite element analysis of the horizontal displacements for different design parameters under a uniform current were compared with the analytical model solutions. It was seen that they had a good level of agreement with their results. The effects of different current speeds and time on the cage shapes were analysed from the finite element results. Further, the mooring forces on the flexible cage for different values of the cage height and cage radius were also presented. The comparison of the results indicated that the numerical model results could be used with confidence in the design of a flexible cylindrical net cage for applications to offshore aquacultures.

scholarly journals Using Unmanned Aerial Vehicle and LiDAR-Derived DEMs to Estimate Channels of Small Tributary Streams

2021 ◽  
Vol 13 (17) ◽  
pp. 3380 ◽  
Author(s):  
Joan Grau ◽  
Kang Liang ◽  
Jae Ogilvie ◽  
Paul Arp ◽  
Sheng Li ◽  
...  
Keyword(s):  
High Resolution ◽  
Unmanned Aerial Vehicle ◽  
Slope Position ◽  
Surface Model ◽  
Stream Channel ◽  
Low Resolution ◽  
Stream Channels ◽  
Aerial Vehicle ◽  
Lidar Dem ◽  
Small Tributary

Defining stream channels in a watershed is important for assessing freshwater habitat availability, complexity, and quality. However, mapping channels of small tributary streams becomes challenging due to frequent channel change and dense vegetation coverage. In this study, we used an Unmanned Aerial Vehicle (UAV) and photogrammetry method to obtain a 3D Digital Surface Model (DSM) to estimate the total in-stream channel and channel width within grazed riparian pastures. We used two methods to predict the stream channel boundary: the Slope Gradient (SG) and Vertical Slope Position (VSP). As a comparison, the same methods were also applied using low-resolution DEM, obtained with traditional photogrammetry (coarse resolution) and two more LiDAR-derived DEMs with different resolution. When using the SG method, the higher-resolution, UAV-derived DEM provided the best agreement with the field-validated area followed by the high-resolution LiDAR DEM, with Mean Squared Errors (MSE) of 1.81 m and 1.91 m, respectively. The LiDAR DEM collected at low resolution was able to predict the stream channel with a MSE of 3.33 m. Finally, the coarse DEM did not perform accurately and the MSE obtained was 26.76 m. On the other hand, when the VSP method was used we found that low-resolution LiDAR DEM performed the best followed by high-resolution LiDAR, with MSE values of 9.70 and 11.45 m, respectively. The MSE for the UAV-derived DEM was 15.12 m and for the coarse DEM was 20.78 m. We found that the UAV-derived DEM could be used to identify steep bank which could be used for mapping the hydrogeomorphology of lower order streams. Therefore, UAVs could be applied to efficiently map small stream channels in order to monitor the dynamic changes occurring in these ecosystems at a local scale. However, the VSP method should be used to map stream channels in small watersheds when high resolution DEM data is not available.

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