Cao and Wang showed that root exudates from strawberries inhibited the growth of strawberries due to autotoxicity. In hydroponics, Kitazawa et al. identified the causal compound of strawberry autotoxicity as benzoic acid. Further, Asao et al. demonstrated that destroying benzoic acid by electrodegradation in hydroponic strawberries increased the plant growth and fruit yield. In soil culture, however, the accumulation and fate of autotoxic compounds in the rhizosphere is not well understood . For example, a toxic level of benzoic acid was absorbed to soil particles, which may explain the reason for the limited allelopathic effect of the compound at concentrations often recorded in natural soil . Overall, the causes of yield decline are complex in general and the exact cause in this study is unknown. However, we demonstrated that the use of the integrated approach can reduce the amount of yield loss, the goal of the study. For example, although each pathogen alone did not cause significant damage, combination of Cylindrocarpon spp., and Pythium spp. caused significant root disease in apple seedlings . More information is needed on how this cropping system would be influenced by rotations with different crops and by emerging pathogens such as Fusarium oxysporum and Macrophomina phaseolina .Actual crop rotations of organic strawberries and vegetables in the central coast of California are complex. Specialized berry growers in California usually lease land and grow strawberries on different fields every year , whereas small-scale organic growers tend to grow both strawberries and vegetables on the same fields. For a specialized organic strawberry grower to rotate fields with other organic vegetable growers, vertical grow choosing which vegetable crops will be used in rotation as done in the present study may not be an option.
Further, if a host crop susceptible to V. dahliae was planted during the break period between strawberries, the level of yield decline can be greater than we found in this study . Finally, the present study demonstrated the positive effect of a longer rotation on strawberry production. In Europe , the Northeast and Midwest United States, and in eastern Canada , a minimum of a three-year rotation is recommended for strawberries that do not use chemical fumigants. Some diversified small-scale organic growers in central coastal California have been maintaining a fiveyear rotation for their strawberries. By diversifying their cropping rotations, they benefit both from improved strawberry yields and access to alternative markets such as farmers’ markets or Community Supported Agriculture systems where greater diversity provides economic advantage . The results of this study justify such practice when it is feasible. ACKNOWLEDGMENTS We express our deep appreciation to Daniel Schmida of Sandpiper Farm who collaborated in designing and managing the field trial, and collecting fruit yield data of the trial. This project was initiated by Robert Stephens, the landowner of the Elkhorn Ranch. He generously loaned the 1acre site for this trial. We thank technical support by Patty Ayala and Katherine E. Kammeijer of UC Cooperative Extension at Salinas, Bree Eagle, David Mendoza, Osvaldo Gomez, Jonah Landor-Yamagata, Alisa LaRue, Mary Sweeters, Susan Lee, Stephanie Garcia, Natalie Lopez, Adam Romero, Loren Mueller, Elizabeth Geisler, Whitney Grover, Amy Hwang, Cameron Joseph Kaplan, Jennifer Leah Smith, Evan Dorroh Watson, Alexa Christine Jones, Jacob Anthony Edmonds, Nebiyu Oluma Demissie, Paul Tho Tran, Jeana Lee, Sara Emery, Balyn Rose, David Griese, Lisa Evans, Nikola Korte, and Pedro Alfonso Garcia Galavís at UCSC.
The project was partially funded by the North American Strawberry Growers Association, the California Strawberry Commission, the Ruth and AlfredHeller Chair in Agroecology at UCSC, the Center for Agroecology and Sustainable Food Systems at UCSC, the Halliday Foundation, the Organic Farming Research Foundation, USDA Integrated Organic Program 2004- 51300-02232, USDA Special Grant 2004-34424-14408, and the Central Coast Regional Water Quality Control Board Non-Point Source Pollution Fund of the Community Foundation for Monterey County. Weather data were kindly provided by the Elkhorn Slough National Estuarine Research Reserve.As fossil fuels supplies continue to dwindle and global warming becomes more of a pressing issue, countries around the world are looking to renewable energy to supply their citizens with clean, reliable, electrical power. Many political leaders, including those from the EU, US, China and Japan have mandated that their countries or states must produce a certain amount of electricity from these sources in the next few decades. Although solar and nuclear energy have their merits, they also exhibit certain drawbacks. Nuclear energy has recently been spurned by governments in Germany and Japan over fears of its safety following the 2011 Fukushima Daiichi disaster. However, nuclear plants can be built on a scale unrivaled by other renewable sources, on the order of gigawatts of power production. As Chinese manufacturers have entered the market, the efficiency of solar panels have been increasing while their unit costs have dropped. However, industrial-scale solar plants, using either photo-voltaic or solar concentrating technology, have not found public acceptance as much as residential rooftop installations. Meanwhile, the installed global capacity of wind energy has been increasing exponentially since the mid-1990s .
Many industry experts believe that most of the ideal onshore installation sites in industrialized countries, such as the EU and US, have been exploited. Offshore wind has emerged as a relatively untapped sustainable resource, especially in deep water. We discuss the plentiful offshore wind resource specifically off of California in Section 1.1.1. Thus far, the cost of deep water offshore wind has prohibited any commercial-scale installations to take place. The technology introduced in this thesis is an attempt to lower the cost of this technology per unit of installed capacity.The oil embargo and ensuing crisis in the 1970s led many governments to increase funding for renewable sources, such as wind energy. At this time, the wind community was testing many different types of wind turbines, including vertical and horizontal axis, with 2-4 blades in upwind and downwind configurations. Considering the main design constraints at the time, which were to maximize sub-MW, land-based turbine efficiency, vertical-axis wind turbines were proven to be inferior. Figure 1.1 compares the power coefficient of a BONUS 37-m horizontal-axis wind turbine with the Sandia 34-m two-speed vertical-axis wind turbine. A turbine’s power coefficient will be defined explicitly in Chapter 3. For now, it can be considered a measure of a turbine’s efficiency. The two-speed, vertical-axis wind turbine exhibits lower performance over the lower wind speeds, although the authors of claim that a true variable speed turbine may reach the performance of a horizontalaxis turbine.This thesis will investigate a novel concept for floating vertical-axis turbines. Specifically, a triangular, semi-submersible floating platform supporting counter-rotating vertical-axis turbines will be investigated. In Chapter 2, we introduce the hydrodynamics of a single, truncated floating cylinder in finite-depth waters undergoing slow-drift motion. The author’s code for this application is bench marked against the results from a well-developed in-house software for a fixed cylinder. The velocity potential, describing the motion of the inviscid fluid particles is expanded in a double perturbation series with respect to the wave amplitude as well as the slow-drift velocities. The slow-drift motion introduces terms, such as the double-body added-mass as well as terms proportional to the amplitude of the response of the fast-scale motions. Furthermore, second-order, steady wave-exciting forces and moments, which can be represented by first-order terms are examined. We introduce how the hydrodynamic force can be transformed from the frequency domain into the time domain so that it can be useful for time-domain simulations. The method is then extended to multiple, interacting, truncated cylinders for the wave-exciting force, which results from the scattering potential. Results are shown in the frequency domain for a three-column, rolling grow table semi-submersible platform that was used for model testing. In Chapter 3 the aerodynamics of vertical-axis wind turbines are discussed. First, a well established blade-element momentum theory called the Double-Multiple Streamtube Method is introduced. The drawbacks of the model, including the need for experimental airfoil lift and drag data and dynamic stall modules motivate the discussion of higher-fidelity simulations of airfoils and turbines. Another in-house fluid dynamics software, utilizing a method known as Implicit Large Eddy Simulations , is briefly presented next. The method is used for three different applications, all of which are in the low-Reynolds regime: first, a single static airfoil over a wide range of angles of attack; second, a simple, two-bladed turbine that has detailed experimental data for validation; third, a pair of counter-rotating turbines with a variable distance between the rotors. These results are used to inform the types of forces to be applied to the model platform.In Chapter 4 we introduce the Multiple Integrated Synchronized Turbine platform. This semi-submersible, three-column platform has two, counter-rotating vertical axis wind turbines on two of the columns.
The turbines are connected in such a way that constrains the turbines to rotate in equal and opposite directions. We discuss the concept of hybrid simulation and its application to the MIST platform. The experimental model platform and the related components, including the drive train, generators, circuit and control implementation are detailed. We briefly discuss the Wind-Input Generator that was used to simulate the effect of the wind turbines on the platform. The communication system, which can send data between the microprocessors on the platform as well as to the datalogger, has redundant wired and wireless technologies. Data from the model tests concerning the open-loop control of the actuation system are presented. In Chapter 5, we numerically recreate the model experiments described in Chapter 4, implementing the theory developed in Chapter 2. We detail how the constraints imposed by the drive train reduce the number of degrees of freedom in the system. In the numerical model, a non-linear control system can be used to control both the yaw position of the platform and the rotational velocity of the turbines. A type of non-linear control, called feedback linearization, is described and used to optimize the power from the turbines. We present results from simulations in the time-domain using the control software SIMULINK when the platform is subject to regular waves. The aerodynamics and hydrodynamics are decoupled, which is shown to be a reasonable assumption due to the minimal pitch and roll motion of the platform in operational sea states. Chapter 6 includes some concluding remarks, including parallels with modern aerospace industry. We describe many of the ways the research could be extended and improved upon in the theoretical, numerical and experimental fields. Finally, we show a commercial development that has been inspired by this research.Data provided in this article includes two simulations using the Variable-Resolution CESM model. CESM version 1.5.5, a fully coupled atmospheric, land, ocean, and sea ice model, was utilized. Both simulations used the F-component set , which prescribes sea-surface temperatures and sea ice but dynamically evolves the atmosphere and land surface component models. The atmospheric component model is the Community Atmosphere Model, version 5.3 with the spectral-element dynamical core in the variable-resolution con- figuration. The VR model grid used for this study, depicted in Fig. 2 from the reference article, was generated for use in CAM and CLM with the open-source software package SQuadGen. On this grid the finest horizontal resolution is 0.125° , with a quasi-uniform 1° mesh over the remainder of the globe. Two simulations were conducted using this grid structure: First, the historical run covers the period from October 1st, 1979 to December 31st, 2000, with first three months discarded as the spin-up period, for a total of 21-years. This historical time period was chosen to provide an adequate sampling of inter-annual variability, to coincide with the time period from the rest of the modeling and reanalysis datasets, and because observed sea surface temperatures were only available through 2005. For projecting future wind energy change, our mid-century simulation ran with the “business as usual” Representative Concentration Pathway 8.5 from October 1st, 2029 to December 31st, 2050, again discarding the first three months for a total of 21-years. Greenhouse gas and aerosol forcing are prescribed based on historical or RCP8.5 concentrations for each simulation. More details on VR-CESM can be found in, and the model has been applied to previous studies.The Det Norske Veritas Germanischer Lloyd Virtual Met product is derived from a hybrid dynamical-statistical downscaling system based upon the Weather Research and Forecasting model and an analog-based ensemble downscaling method.