Harmful algal bloom management and response: assessment and plan

This report, "Harmful Algal Bloom Management and Response: Assessment and Plan" reviews and evaluates Harmful Algal Bloom (HAB) management and response efforts, identifies current prevention, control, and mitigation programs for HABs, and presents an innovative research, event response, and infrastructure development plan for advancing the response to HABs. In December 2004, Congress enacted and the President signed into law the Harmful Algal Bloom and Hypoxia Amendments Act of 2004, (HABHRCA 2004). The reauthorization of HABHRCA acknowledged that HABs are one of the most scientifically complex and economically damaging coastal issues challenging our ability to safeguard the health of our Nation’s coastal ecosystems. The Administration further recognized the importance of HABs as a high priority national issue by specifically calling for the implementation of HABHRCA in the President’s U.S. Ocean Action Plan. HABHRCA 2004 requires four reports to assess and recommend research programs on HABs in U.S. waters. This document comprises two linked reports specifically aimed at improving HAB management and response: the Prediction and Response Report and the follow-up plan, the National Scientific Research, Development, Demonstration, and Technology Transfer (RDDTT) Plan on Reducing Impacts from Harmful Algal Blooms. This document was prepared by the Interagency Working Group on Harmful Algal Blooms, Hypoxia, and Human Health, which was chartered through the Joint Subcommittee on Ocean Science and Technology of the National Science and Technology Council and the Interagency Committee on Ocean Science and Resource Management Integration. This report complements and expands upon HAB-related priorities identified in Charting the Course for Ocean Science in the United States for the Next Decade: An Ocean Research Priorities Plan and Implementation Strategy, recently released by the Joint Subcommittee on Ocean Science and Technology. It draws from the contributions of numerous experts and stakeholders from federal, state, and local governments, academia, industry, and non-governmental organizations through direct contributions, previous reports and planning efforts, a public comment period, and a workshop convened to develop strategies for a HAB management and response plan. Given the importance of the Nation’s coastal ocean, estuaries, and inland waters to our quality of life, our culture, and the economy, it is imperative that we move forward to better understand and mitigate the impacts of HABs which threaten all of our coasts and inland waters. This report is an effort to assess the extent of federal, state and local efforts to predict and respond to HAB events and to identify opportunities for charting a way forward

Size-dependent optical properties of VO2 nanoparticle arrays

The size effects on the optical properties of vanadium dioxide nanoparticles in ordered arrays were investigated. It was observed that the optical contrast between the semiconducting and metallic phases is enhanced in the visible region, presenting size-dependent optical resonances and size-dependent transition temperatures. The collective optical response as a function of temperature was found to present an enhanced scattering state during the evolving phase transition. These observations were suggested to provide critical insights into statistical processes occurring in materials at the nanoscale

Two-dimensional current percolation in nanocrystalline vanadiumdioxide films

Simultaneous measurements of the transmittance and the resistance were carried out on 20-nm-thick VO2 wires during the semiconductor-to-metal transition (SMT). They reveal an offset between the effective electrical and optical switching temperatures. This shift is due to current percolation through a network of nanometer-scale grains of different sizes undergoing a SMT at distinct temperatures. An effective-medium approximation can model this behavior and proves to be an indirect method to calculate the surface coverage of the films

Semiconductor to metal phase transition in the nucleation and growth of VO2 nanoparticles and thin films

X-ray diffraction (XRD) and Rutherford backscattering were used for investigating the morphological and optical properties of vanadium dioxide nanoparticles and thin films during their nucleation and growth phases. The processing parameters were correlated in accordance with the temperature and sharpness of the transition. Grain growth and improved crystallinity resulted from thermal annealing. Because of fewer nucleating defects within the volume, the improved crystal perfection led to a large hysteresis. The effects of grain size and crystallinity determined the shape and width of the hysteresis cycle

Synthesis and characterization of size-controlled vanadium dioxide nanocrystals in a fused silica matrix

Vanadium dioxide single-crystal precipitates with controlled particle sizes were produced in an amorphous, fused SiO 2 host by the stoichiometric coimplantation of vanadium and oxygen ions and subsequent thermal processing. The effects of the vanadium dioxide nanocrystal size, nanocrystal morphology, and particle/host interactions on the VO 2 semiconductor-to-metal phase transition were characterized. VO 2 nanoparticles embedded in amorphous SiO 2 exhibit a sharp phase transition with a hysteresis that is up to 50°C in width - one of the largest values ever reported for this transition. The relative decrease in the optical transmission in the near-infrared region in going from the semiconducting to the metallic phase of VO 2 ranges from 20% to 35%. Both the hysteresis width and the transition temperature are correlated with the size of the precipitates. Doping the embedded VO 2 particles with ions such as titanium alters the characteristics of the phase transition, pointing the way to control the hysteresis behavior over a wide range of values and providing insight into the operative physical mechanisms

Size effects in the structural phase transition of VO2 nanoparticles

We have observed size effects in the structural phase transition of submicron vanadium dioxide precipitates in silica. The VO2 nanoprecipitates are produced by the stoichiometric coimplantation of vanadium and oxygen and subsequent thermal processing. The observed size dependence in the transition temperature and hysteresis loops of the semiconductor-to-metal phase transition in VO2 is described in terms of heterogeneous nucleation statistics with a phenomenological approach in which the density of nucleating defects is a power function of the driving force

Enhanced hysteresis in the semiconductor-to-metal phase transition of VO2 precipitates formed in SiO2 by ion implantation

A strongly enhanced hysteresis with a width of >34°C has been observed in the semiconductor-to-metal phase transition of submicron-scale VO2 precipitates formed in the near-surface region of amorphous SiO2 by the stoichiometric coimplantation of vanadium and oxygen and subsequent thermal processing. This width is approximately an order of magnitude larger than that reported previously for the phase transition of VO2 particles formed in Al2O3 by a similar technique. The phase transition is accompanied by a significant change in infrared transmission. The anomalously wide hysteresis loop observed here for the VO2/SiO2 system can be exploited in optical data storage and switching applications in the infrared region

Modulated optical transmission of subwavelength hole arrays in metal- v O 2 films

We demonstrate the modulation of the transmission of near-infrared light through a periodic array of subwavelength apertures in Ag-V O2 and Au-V O2 double-layer films using the semiconductor-to-metal phase transition in V O2. The transmitted intensity ratio increases by a factor of 8 as the V O2 goes from the semiconductor to the metal phase. We attribute this modulation to the switchable dielectric-permittivity contrast between the air-filled holes in the array and the surrounding V O2 material, a conjecture that is semiquantitatively confirmed by simulation

Switchable reflectivity on silicon from a composite VO 2-SiO 2 protecting layer

The production of near-surface nanocomposites with a thermally variable reflectivity on single crystal Si using ion beams and thermal processing was presented. Stoichiometric coimplantation of vanadium and oxygen ions and subsequent thermal processing were employed to form embedded VO 2 nanoparticles in the SiO 2 film. It was observed that the reflectivity of the vanadium dioxide particles underwent a large changes at the VO 2 semiconductor-to-metal phase transition. The reflectivity of the vanadium dioxide particles which underwent large changes provide a mechanism for thermally controlling the reflectivity of the VO 2/SiO 2/Si layer and effectively, the Si crystal surface