Portable Tower Research Articles

Physical structure and biological composition of canopies in tropical secondary and old-growth forests.

The area of tropical secondary forests is increasing rapidly, but data on the physical and biological structure of the canopies of these forests are limited. To obtain such data and to measure the ontogeny of canopy structure during tropical rainforest succession, we studied patch-scale (5 m2) canopy structure in three areas of 18–36 year-old secondary forest in Costa Rica, and compared the results to data from old-growth forest at the same site. All stands were sampled with a stratified random design with complete harvest from ground level to the top of the canopy from a modular portable tower. All canopies were organized into distinct high- and low-leaf-density layers (strata), and multiple strata developed quickly with increasing patch height. The relation of total Leaf Area Index (LAI, leaf area per area of ground) to patch canopy height, the existence of distinct high and low leaf- density layers (strata and free air spaces), the depth and LAI of the canopy strata and free air spaces, and the relation of the number of strata to patch canopy height were remarkably constant across the entire successional gradient. Trees were the most important contributor to LAI at all stages, while contribution of palm LAI increased through succession. We hypothesize that canopy physical structure at the patch scale is driven by light competition and discuss how this hypothesis could be tested. That canopy physical structure was relatively independent of the identity of the species present suggests that canopy physical structure may be conserved even as canopy floristics shift due to changing climate.

Adverse impacts of mobile phone tower radiation on human health

These days mobile phones have become associated with elementary a part of our life, this is often one in every of the foremost necessary mediums for communication. Consequently, several portable towers are planted to hide additional areas, particularly in huddled cities and concrete areas. Now, the bottom stations made on these locations have transceivers that employ mistreatment frequency (RF) waves to determine communication among users within the mobile network. Because of the variety of base stations needed it will increase with bigger portable use with market competition, and with new technological capabilities. The microwave frequencies utilized in mobile communication cause thermal and non-thermal effects and leave a negative impact on the biological system. The quantity of RF-EMW radiation energy absorbed by human tissue depends on the frequency, intensity, polarization, and period of exposure. The EMR is recognized because of the major reason behind cancer. This review paper presents the potential biological and medicine health effects of high-intensity portable tower radiation.

Impact of Work Zone Lighting on Driver's Detection of Objects

Researchers conducted a closed-course study to evaluate the impact of work zone lighting on the ability of drivers to detect low-contrast objects and workers wearing high-visibility vests. Three lighting conditions were set up: no lights (dark or base condition); a portable, trailer-mounted light tower; and a portable balloon light. The dark scenario treatments confirmed that a worker wearing a retroreflective vest could be detected at significantly longer distances than a low-contrast object (a box, a target, and a tire). Researchers also confirmed that drivers tended to overdrive their headlights, especially in rural, dark scenarios. Compared with the results for the dark scenarios, the results for the illuminated roadway section showed that properly installed temporary work zone lighting could increase the distance at which workers and low-contrast objects could be detected. The results also confirmed that improper positioning of portable light towers had a negative impact on the distance at which workers and low-contrast objects could be detected and supported the theory that direct illumination by portable light towers could visually wash out workers and thus could make them more difficult to detect.

Wind Patterns over a Heliostat Field

Heliostats constitute a major portion of the direct costs of a concentrating solar power tower plant. As a result, a significant amount of effort is being focused on designing and developing cheaper heliostats. The optical and structural performance of these new and existing heliostats under dynamic wind loads must be characterized and understood in order to meet both cost and performance objectives. This paper presents the second phase of a U.S. DOE-sponsored program at Sandia National Laboratories’ National Solar Thermal Test Facility (NSTTF) that includes dynamic testing and analysis of multiple full-scale heliostats. The objectives of these tests and analyses are to characterize and understand some differences in the impacts of dynamic wind loads on heliostat strain and cyclic fatigue between perimeter and inner-field heliostats.A weather tower with three tri-axial ultrasonic anemometers has been erected just outside the field to measure the approaching boundary winds, while a portable tower was set up to characterize wind velocities and turbulence between subsequent rows within the field. Anemometers have also been mounted to some heliostats to gather close range measurement of turbulence and wind frequencies and to provide a point of comparison for computational fluid dynamics models of wind flow over the field.This paper presents mean wind speeds and wind loads on heliostats as a function of field position. The calculated mean wind loads were used to assess the mean wind-load reduction correlation of Peterka [1].

Design, development and deployment of a hybrid renewable energy powered mobile medical clinic with automated modular control system

Abstract A renewable energy powered mobile medical clinic has been designed, developed and deployed in the Dominican Republic. The portable renewable energy system consists of a 46.5 m 2 (500 ft 2 ) tent powered by a suite of renewable energy technologies including a hybrid wind and photovoltaic system with a lithium-iron-phosphate (LiFePO 4 ) battery bank for energy storage. Thin-film photovoltaic panels integrated into the thermal fly of the tent are designed to generate 4.8 kW of power. In addition, the system consists of two wind turbines each capable of generating 1 kW, and are supported on portable towers which do not require guy wires or mountings into the ground. The system provides 3 kW of power continuously with a maximum renewable energy power generation of 6.8 kW. The Mobile Medical Clinic (MMC) was deployed in Mao, Dominican Republic. Due to the environmental conditions at this particular location a majority of the power generated by the renewable energy system came from the photovoltaic panels. The renewable energy system and energy storage system are backed up by a gasoline generator, which serves solely as a source of power in the absence of wind or solar energy and when the battery bank is discharged. The control system of the MMC automatically turns on and shuts off the generator as needed in order to minimize fuel consumption. The entire MMC including the renewable energy system was designed to be portable, scalable and all components man-liftable. The system is controlled by state-of-the-art off the shelf components and does not require a complex computer control system. The control system consists solely of the inverters and the charge controllers. The system has remained extremely effective and yet simple to operate which is beneficial since the purpose of the MMC is to operate in austere conditions with minimal training for the operators. The system has been donated to the Dominican Republic to be used for deployment during emergency response situations.

Continuous measurements of net CO2 exchange by vegetation and soils in a suburban landscape

In a suburban neighborhood of Minneapolis–Saint Paul, Minnesota, USA, we simultaneously measured net CO2 exchange of trees using sap flow and leaf gas exchange measurements, net CO2exchange of a turfgrass lawn using eddy covariance from a portable tower, and total surface‐atmosphere CO2 fluxes (FC) using an eddy covariance system on a tall tower. Two years of continuous measurements showed that net CO2exchange varied among vegetation types, with the largest growing‐season (Apr–Nov) net CO2 uptake on a per cover area basis from evergreen needleleaf trees (−603 g C m−2), followed by deciduous broadleaf trees (−216 g C m−2), irrigated turfgrass (−211 g C m−2), and non‐irrigated turfgrass (−115 g C m−2). Vegetation types showed seasonal patterns of CO2exchange similar to those observed in natural ecosystems. Scaled‐up net CO2 exchange from vegetation and soils (FC(VegSoil)) agreed closely with landscape FC measurements from the tall tower at times when fossil fuel emissions were at a minimum. Although FC(VegSoil) did not offset fossil fuel emissions on an annual basis, the temporal pattern of FC(VegSoil) did significantly alter the seasonality of FC. Total growing season FC(VegSoil)in recreational land‐use areas averaged −165 g C m−2 and was dominated by turfgrass CO2 exchange (representing 77% of the total), whereas FC(VegSoil) in residential areas averaged −124 g C m−2 and was dominated by trees (representing 78% of the total). Our results suggest urban vegetation types can capture much of the variability required to predict seasonal patterns and differences in FC(VegSoil) that could result from changes in land use or vegetation composition in temperate cities.

Atmospheric monitoring of a perfluorocarbon tracer at the 2009 ZERT Center experiment

Abstract Field experiments at Montana State University are conducted for the U.S. Department of Energy as part of the Zero Emissions Research and Technology Center (ZERT) to test and verify monitoring techniques for carbon capture and storage (CCS). A controlled release of CO 2 with an added perfluorocarbon tracer was conducted in July 2009 in a multi-laboratory study of atmospheric transport and detection technologies. Tracer plume dispersion was measured with various meteorological conditions using a tethered balloon system with Multi-Tube Remote Samplers (MTRS) at elevations of 10 m, 20 m, and 40 m above ground level (AGL), as well as a ground-based portable tower with monitors containing sorbent material to collect the tracer at 1 m, 2 m, 3 m, and 4 m AGL. Researchers designed a horizontal grid of sampling locations centered at the tracer plume source, with the tower positioned at 10 m and 30 m in both upwind and downwind directions, and the MTRS spaced at 50 m and 90 m downwind and 90 m upwind. Tracer was consistently detected at elevated concentrations at downwind sampling locations. With very few exceptions, higher tracer concentrations correlated with lower elevations. Researchers observed no statistical difference between sampling at 50 m and 90 m downwind at the same elevation. The US EPA AERMOD model applied using site-specific information predicted transport and dispersion of the tracer. Model results are compared to experimental data from the 2009 ZERT experiment. Successful characterization of the tracer plume simulated by the ZERT experiment is considered a step toward demonstrating the feasibility of remote sampling with unmanned aerial systems (UAS’s) at future sequestration sites.

Use of a Portable Tower and Remote-controlled Launcher to Improve Physical Conditioning in a Rehabilitating Wild Mallard (Anas platyrhynchos)

Prerelease reconditioning improves the chance of survival of rehabilitating raptors. Reconditioning may also help to rehabilitate waterfowl, including those that are threatened or endangered, especially if the birds are released during periods of migration. A flying harness, creance, remote-controlled launcher, and portable tower were used to create a means of reconditioning a rehabilitating 5-month-old female wild mallard duck (Anas platyrhynchos) that had been housed in a rehabilitation center for 7 weeks while recovering from an injury. Pre- and postflight serum lactate levels, body condition index scores, and controlled flight distances were used to assess the bird's degree of conditioning. Postflight serum lactate levels never returned to preflight levels and were not deemed a reliable indicator of physical fitness. However, the mallard showed an increase in endurance and strength as well as improved body condition index scores over the course of the reconditioning program.

Command Generation for Flexible Systems by Input Shaping and Command Smoothing

DOI: 10.2514/1.50270Aggressive motions are often discouraged when a system has flexible dynamics. Common practice suggests thatsmooth commands, such as S-curves, should be used to drive the system. However, smooth commands cannot beimplementedonsomeactuators,suchastheon/offthrustersusedonspacecraftoron/offvalvesusedwithhydraulicsand pneumatics. Furthermore, smooth commands can lead to sluggish response. A rigorous comparison of smoothand nonsmooth reference commands is presented in this paper. The evaluation is performed by treating smoothcommandprofilesasinput-shapedfunctions.Inputshapingisamethodofreducingresidualvibrationbyconvolvinga sequence of impulses with a baseline reference command. By interpreting smooth commands as input-shapedfunctions, a common criterion for comparing smooth and nonsmooth commands is developed. The results of thiscomprehensive comparison indicate that input-shaped step functions are usually more efficient for reducingvibration than commonly used smooth commands. A portable tower crane is used to experimentally verify thecomparison between input-shaped and smooth commands.

Reconstruction of Hurricane Katrina's wind fields for storm surge and wave hindcasting

As the most costly US natural disaster in history, Hurricane Katrina fostered the IPET forensic study to better understand the event. All available observations from several hundred space-, land-, sea-, and aircraft-based measurement platforms were gathered and processed to a common framework for height, exposure, and averaging time, to produce a series of wind field snapshots at 3 h intervals to depict the wind structure of Katrina when in the Gulf of Mexico. The stepped-frequency microwave radiometer was calibrated against GPS sondes to establish the upper range of the instrument and then used to determine the wind field in the storm's core region in concert with airborne Doppler radar winds adjusted to the surface from near the top of the PBL (500 m). The SFMR data were used to develop a method to estimate surface winds from 3 km level reconnaissance aircraft observations, taking into consideration the observed azimuthal variation of the reduction factor. The “SFMR method” was used to adjust reconnaissance flight-level measurements to the surface in the core region when SFMR and Doppler winds were not available. A variety of coastal and inland mesonet data were employed, including portable towers deployed by Texas Tech University, University of Louisiana at Monroe, and the Florida Coastal Monitoring Program, as well as fixed mesonet stations from Louisiana State Universities Marine Consortium, University of Southern Mississippi, and Agricultural Networks from Louisiana, Mississippi, and Alabama, and the Coastal Estuarine Network of Alabama and Mississippi. Also included were land- (WSR-88D VAD and GBVTD, ASOS, Metar, LLWAS, HANDAR), space- (QuikScat, GOES cloud drift winds, WindSat), and marine- (GPS sondes, Buoys, C-MAN, ships) platforms. The wind fields serve as an analysis of record and were used to provide forcing for wave and storm surge models to produce hindcasts of water levels in the vicinity of flood control structures.

GuylinePC: An Interactive Guyline Tension Analysis Program for Guyed Logging Towers

Abstract In the US Pacific Northwest and other mountainous regions, cable yarding using portable steel towers is a common harvesting system in steep terrain. These systems are expensive and can be unsafe if improperly rigged. For both economic and safety considerations, configurations are used that ensure that the system can sustain the forces applied during yarding operations. We present a computer-based application, GuylinePC, for evaluating the guyline and anchor loads resulting from an applied load. Our model extends the usability and scope of a model previously developed by other researchers. Specifically we (1) provide a more modern graphical user interface, (2) use optimization methods to determine equilibrium states, and (3) illustrate the capability of the program to be used in design. We briefly discuss the analytical model and software application and present a design problem. The program is intended to improve a forest engineer's understanding of cable yarding systems.

Foliar and ecosystem respiration in an old‐growth tropical rain forest

Foliar respiration is a major component of ecosystem respiration, yet extrapolations are often uncertain in tropical forests because of indirect estimates of leaf area index (LAI). A portable tower was used to directly measure LAI and night-time foliar respiration from 52 vertical transects throughout an old-growth tropical rain forest in Costa Rica. In this study, we (1) explored the effects of structural, functional and environmental variables on foliar respiration; (2) extrapolated foliar respiration to the ecosystem; and (3) estimated ecosystem respiration. Foliar respiration temperature response was constant within plant functional group, and foliar morphology drove much of the within-canopy variability in respiration and foliar nutrients. Foliar respiration per unit ground area was 3.5 +/- 0.2 micromol CO2 m(-2) s(-1), and ecosystem respiration was 9.4 +/- 0.5 micromol CO2 m(-2) s(-1)[soil = 41%; foliage = 37%; woody = 14%; coarse woody debris (CWD) = 7%]. When modelled with El Niño Southern Oscillation (ENSO) year temperatures, foliar respiration was 9% greater than when modelled with temperatures from a normal year, which is in the range of carbon sink versus source behaviour for this forest. Our ecosystem respiration estimate from component fluxes was 33% greater than night-time net ecosystem exchange for the same forest, suggesting that studies reporting a large carbon sink for tropical rain forests based solely on eddy flux measurements may be in error.

Performance Evaluation of Semipermanent High-Mast Lighting for Highway Construction Projects

In 2005, the New York State Department of Transportation authorized the first-time use of semipermanent, high-mast, pole-mounted luminaires to illuminate nighttime road work construction and maintenance. This approach was used along a 3-mi stretch of Interstate 90 in Albany, New York, as an alternative to portable light towers. The performance of the high-mast lighting system is assessed according to the criteria of construction work quality and safety and visibility for workers and drivers. The high-mast lighting system was found to have met lighting performance specifications. Field measurements and an analytical comparison of the high-mast lighting with the portable light towers suggested that the high-mast lighting system provided sufficient illumination for performing maintenance and construction activities at the site, with few shadows and relatively low glare, thereby increasing visibility of hazards and improving performance of visual tasks for both workers and motorists. On the basis of these analyses, the high-mast lighting system should provide a higher level of safety than the portable light towers for the construction workers and for the drivers traveling through the construction zone for this project. The high-mast lighting system should also reduce the risk of injury to construction workers during high-exposure times when they would be setting up and removing portable lighting equipment. Other considerations, such as the implications for conditions of wet pavement and mesopic vision, are explored.

Implementing Semipermanent High-Mast Lighting for Highway Construction Projects

Semipermanent, high-mast pole-mounted lighting for nighttime road work construction and maintenance was implemented based on an installation along Interstate 90 in Albany, New York. The high-mast lighting system met state lighting performance specifications. There were no recorded accidents at the site during the construction period. Although that result is largely attributable to roadway closures allowed during part of the project, consensus of the contractor and transportation agency is that the lighting increased safety. The cost of the high-mast lighting system was approximately 16% higher than the estimated cost of the portable light towers. Despite the higher estimated cost of the high-mast lighting system, the economic and societal benefits seem considerable in this particular location, an urban, heavily traveled throughway. In particular, this lighting method probably shortened the time required for the construction, reducing the amount of risk to workers and drivers and reducing traffic delays for motorists. This paper identifies projects where this lighting technique might be appropriate.

Useful applications of closed-loop signal shaping controllers

Input shaping is a well-established open-loop technique used for reducing the vibratory response of dynamic systems. Some researchers have investigated the stability and utility of using this technique within a feedback control loop. The main contribution of the prior investigations was to identify stable configurations of in-the-loop input shaping systems. This paper identifies three promising applications of the stable controllers. Performance comparisons are made between the in-the-loop input shaping systems and more conventional feedback control strategies. Experimental results from a 10-ton industrial bridge crane, a portable bridge crane, and a portable tower crane are used to demonstrate the utility of the closed-loop input shaping control architecture.

AN INTERNET-DRIVEN TOWER CRANE FOR DYNAMICS AND CONTROLS EDUCATION

An advanced controls class taught at both the Georgia Institute of Technology and the Tokyo Institute of Technology focuses on command generation, remote manipulation, and human interaction with control systems. To aid in teaching these concepts, a portable tower crane was constructed. The tower crane can follow pre-programmed trajectories or be driven manually. It can also be operated from anywhere in the world with an internet connection. The crane can perform both feedback and command shaping anti-swing control while measuring trolley position and payload swing. The system enables students to perform a variety of useful and interesting laboratories and student projects. The students participated in and studied the effects of remote operator behavior, non-linear system dynamics, and advanced command generation techniques. The paper describes the tower crane and the results of this new educational endeavor.

Canopy scale measurements of CO2 and water vapor exchange along a precipitation gradient in southern Africa

AbstractShort‐term measurements of carbon dioxide, water, and energy fluxes were collected at four locations along a mean annual precipitation gradient in southern Africa during the wet (growing) season with the purpose of determining how the observed vegetation–atmosphere exchange properties are functionally related to the long‐term climatic conditions. This research was conducted along the Kalahari Transect (KT), one in the global set of International Geosphere‐Biosphere Program transects, which covers a north–south aridity gradient, all on a homogenous sand formation. Eddy covariance instruments were deployed on a permanent tower in Mongu, Zambia (879 mm of rainfall per year), as well as on a portable tower in Maun (460 mm yr−1), Okwa River Crossing (407 mm yr−1), and Tshane (365 mm yr−1), Botswana for several days at each site. The relationships between CO2 flux, Fc, and photosynthetically active radiation were described well by a hyperbolic fit to the data at all locations except for Mongu, the wettest site. Here, there appeared to be an air temperature effect on Fc. While daytime values of Fc routinely approached or exceeded −20 μmol m−2 s−1 at Mongu, the magnitude of Fc remained less than −10 μmol m−2 s−1 when the air temperature was above 27°C. Canopy resistances to water vapor transfer, rc, displayed an overall decline from the wetter sites to the more arid sites, but the differences in rc could be almost exclusively accounted for by the decrease in leaf area index (LAI) from north to south along the KT. Ecosystem water use efficiency (WUE), defined as the ratio of net carbon flux to evapotranspiration, showed a general decrease with increasing vapor pressure deficit, D, for all of the sites. The magnitudes of WUE at a given D, however, were dissimilar for the individual sites and were found to be stratified according to the position of the sites along the long‐term aridity gradient. For example, Mongu, which has the wettest climate, has a much lower WUE for like levels of D than Tshane, which historically has the most arid climate. Given the similar inferred stomatal resistances between the sites, the disparate carbon uptake behavior for the grass vs. woody vegetation is the likely cause for the observed differences in WUE along the aridity gradient. The short‐term flux measurements provide a framework for evaluating the vegetation's functional adaptation to the long‐term climate and provide information that may be useful for predicting the dynamic response of the vegetation to future climate change.

Measurement and use of the vertical gravity gradient in correcting repeat microgravity measurements for the effects of ground subsidence in geothermal systems

Changes in mass resulting from production and reinjection in geothermal fields can be monitored using repeat microgravity measurements. The measured changes in gravity, however, need to be corrected for the effects of any exploitation-induced ground subsidence. The correction required at each measurement point is the product of the amount of ground subsidence and the vertical gravity gradient at that point. Measurements of the gravity gradient, made using a portable tower, show that it varies from place to place depending mainly on the local topography. Measured gradients, in areas of high subsidence rate, range between −276 and −339 μgal/m at 30 sites in the Wairakei–Tauhara field and between −296 and −321 μgal/m at nine sites in the Ohaaki field (New Zealand). These values are similar to those used previously. At 37 sites measured in the Yanaizu–Nishiyama field (Japan) the gradient varied between −244 and −352 μgal/m. Measurements at six sites showed no significant change in gravity gradient with height above the ground surface; a single value for the gradient can therefore be used at each site to correct for the gravitational effect of any ground movement. Calculations show the effects on the vertical gravity gradient of groundwater level variations, mass changes associated with the ground subsidence, and reservoir mass changes are negligible at Wairakei.

Heat Budget Calculation in the Convective Boundary Layer on a 4 × 4 Vertical versus Time Grid from Aircraft and Surface Measurements

Aircraft, portable tower, and radiosonde measurements from 4 August 1989 (day 68) of the First International Satellite Land Surface Climatology Project (ISLCP) Field Experiment (FIFE), over fairly flat terrain in Kansas, are used for the reconstruction of the heat conservation equation. The calculation grid consists of three grouped flight levels and the surface, and three 1-h blocks, within the midday convective boundary layer (CBL). The day chosen had a week warm front disturbance in addition to the usual summertime southern flow over the midwestern United States. Significant vertical and temporal structure, which should not be bulk averaged, was observed for all terms. The upper layer showed warming sustained at a constant rate around noon and appeared decoupled from the surface and the middle levels in the later hours. Excess warming was due to advection and possibly entrainment. Consequently, the heat flux divergence also had a nonzero vertical gradient. Advection proves to be an important term and does not average out when driven by a synoptic feature. Its east–west component improved the balance of the heat equation at all levels. Partial flight intertrack and total CBL volume standard deviations for terms and residuals are carried through explicitly.

The Portable Tower Works

The Portable <i>Tower Works</i>