793 research outputs found

    An Annotated Bibliography of Survey and Analysis Methods for Study of Indigenous Agroforestry Systems

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    The issues surrounding land use in tropical countries have led to many studies of indigenous traditional land uses. In recent years, those agricultural systems incorporating trees (termed agroforestry) have been subjected to particular scrutiny. Students of agroforestry systems are faced with choosing among methods from a variety of disciplines, including agriculture, anthropology, range management, forestry, sociology, and economics. One of the most difficult decisions in planning and conducting such studies is which methods to use and why. The purpose of this annotated bibliography is to highlight the survey and analysis methods used in a select group of publications spanning a variety of scale, purpose, and detail.Land Grant Institutions of the Pacific: American Samoa Community College, College of Micronesia, Northern Marianas Community College, University of Guam, and University of Hawai'i, through the Agricultural Development in the American Pacific (ADAP) Project. Funded through the US Department of Agriculture Cooperative Extension Service

    Non equilibrium anisotropic excitons in atomically thin ReS2_2

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    We present a systematic investigation of the electronic properties of bulk and few layer ReS2_2 van der Waals crystals using low temperature optical spectroscopy. Weak photoluminescence emission is observed from two non-degenerate band edge excitonic transitions separated by \sim 20 meV. The comparable emission intensity of both excitonic transitions is incompatible with a fully thermalized (Boltzmann) distribution of excitons, indicating the hot nature of the emission. While DFT calculations predict bilayer ReS2_2 to have a direct fundamental band gap, our optical data suggests that the fundamental gap is indirect in all cases

    Observation of Ag1_g^1 Raman mode splitting in few layers black phosphorus encapsulated with hexagonal boron nitride

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    We investigate the impact of the encapsulation with hexagonal boron nitride (h-BN) on the Raman spectrum of few layer black phosphorus. The encapsulation results in a significant reduction of the line width of the Raman modes of black phosphorus, due to a reduced phonon scattering rate. We observe a so far elusive peak in the Raman spectra \sim4cm1^{-1} above the Ag1_{\text{g}}^1 mode in trilayer and thicker flakes, which had not been observed experimentally. The newly observed mode originates from the strong black phosphorus inter-layer interaction, which induces a hardening of the surface atoms vibration with respect to the corresponding modes of the inner layers. The observation of this mode suggests a significant impact of h-BN encapsulation on the properties of black phosphorus and can serve as an indicator of the quality of its surface.Comment: 15 pages, 4 figures just accepted for publication in Nanoscale http://pubs.rsc.org/en/Content/ArticleLanding/2017/NR/C7NR05588A#!divAbstrac

    Determination of the parameters of semiconducting CdF2:In with Schottky barriers from radio-frequency measurements

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    Physical properties of semiconducting CdF_2 crystals doped with In are determined from measurements of the radio-frequency response of a sample with Schottky barriers at frequencies 10 - 10^6 Hz. The dc conductivity, the activation energy of the amphoteric impurity, and the total concentration of the active In ions in CdF_2 are found through an equivalent-circuit analysis of the frequency dependencies of the sample complex impedance at temperatures from 20 K to 300 K. Kinetic coefficients determining the thermally induced transitions between the deep and the shallow states of the In impurity and the barrier height between these states are obtained from the time-dependent radio-frequency response after illumination of the material. The results on the low-frequency conductivity in CdF_2:In are compared with submillimeter (10^{11} - 10^{12} Hz) measurements and with room-temperature infrared measurements of undoped CdF_2. The low-frequency impedance measurements of semiconductor samples with Schottky barriers are shown to be a good tool for investigation of the physical properties of semiconductors.Comment: 9 pages, 7 figure

    Study of Metrological Properties of Voltammetric Electrodes in the Time Domain

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    Metrological properties of voltammetric electrodes, in the situation where on their surface an electrochemical reaction of oxidizing/reduction takes place, were analyzed in this chapter. The properties of electrodes on which a reaction controlled by ion transport process takes place were taken into consideration. Also, it was analyzed how the electrode’s shape and the voltage polarizing the electrode influence this electrode’s metrological properties. The result of the analysis conducted is that in case of a reaction controlled by charge exchange process, such a voltammetric electrode functions like a converter type 0. Its metrological properties in the time domain are defined solely by sensitivity. However, if on the surface of the electrode there is a reaction controlled by ion transport process, the electrode will function like a converter type I. Its metrological properties in the time domain are defined by the sensitivity and time constant. Numeric simulations were conducted in order to determine the influence of the electrode’s shape and the polarizing voltage on metrological properties of the electrode. The results show that both the sensitivity and the time constant of the electrode can be influenced by choice of an electrode’s shape and the shape of the polarizing voltage

    The Role of Phototaxis in the Initial Swim Bladder Inflation of Larval Yellow Perch (Perca Flavescens).

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    The North Central Regional Aquaculture Center has designated the yellow perch (Perca flavescens) as a high priority species for culture. The demand for this species is high and it is estimated that the market could readily consume 50 to 100 million pounds per year. Tank culturing of yellow perch has several advantages over pond culture and this method has been growing in popularity, but is currently held back by problems in larval development. One of these problems, failed swim bladder inflation (SBI), is frequently reported in the literature as a bottleneck in the culture of many fishes. Unsuccessful SBI increases metabolic demands, inhibits prey capture, and increases a fish’s overall probability of death. Initial SBI can occur within a finite period during ontogeny, and missing this opportunity results in permanent malformation of the organ. Advances in this problem have been made, but the challenge of increasing SBI success remains. The literature suggests that light cues appear to trigger the response of rising to the surface to gulp air and initially inflate. The yellow perch is photopositive in the larval phase and this phototactic response correlates with the window of opportunity for SBI to occur. The goal of this research was to examine the role that phototactic behavior plays in initial SBI in yellow perch. The results of this study reveal that low-intensity nighttime light reduces the proportion of perch larvae to initially inflate. It seems that the photopositive response does not contribute to SBI success, and in fact it can significantly hinder the process when light sources exist below the water’s surface. This could potentially explain previous research where increased SBI is seen in tanks with less reflective internal surfaces, and suggests that nighttime lighting and below surface light should be reduced as much as possible to increase SBI success

    Luminescent and scintillation properties of Ce3+ doped Ca2RMgScSi3O12 (R = Y, Lu) single crystalline films

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    The work is dedicated to the growth and investigation of the luminescent and scintillation properties of single crystalline films (SCFs) of Ca2-xR1+xMg1+xSc1-xSi3O12:Ce (R = Y, Lu) mixed garnets with x = 0-0.25, grown using the liquid phase epitaxy method onto Y3Al5O12 substrates from PbO-B2O3 based flux. The absorption, luminescent and scintillation properties of Ca2-xY1+xMg1+xSc1-xSi3O12:Ce and Ca2-xLu1+xMg1+xSc1-xSi3O12:Ce SCFs with x = 0 and 0.25 were investigated and compared with the reference YAG:Ce and LuAG:Ce SCFs. Using the Ca2+, Mg2+ and Si4+ alloying, the Ce3+ emission spectra in Ca2-xR1+xMg1+xSc1-xSi3O12:Ce (R = Y, Lu; x = 0-0.25) SCFs can be notably extended in the red range in comparison with YAG: Ce and LuAG: Ce SCFs due to the increase of crystal field strength and Ce3+ multicenter creation in the dodecahedral positions of the lattices of these mixed garnet compounds. Due to the formation of Ce4+ ions, the as-grown Ca2-xR1+xMg1+xSc1-xSi3O12:Ce (R = Y, Lu) SCFs at x = 0 and 0.25 show relatively low light yield. However, after annealing in reducing atmosphere (95% N-2 + 5% H-2) at T > 1000 degrees C, a recharging Ce4+ -> Ce3+ takes place. After that, these SCFs possess the light yield about of 30% and 31% in comparison with the reference YAG: Ce and LuAG: Ce SCFs, respectively, and a fast scintillation response with the decay times in the ns range under a-particles excitation by Pu-239 (5.15 MeV) source

    Terrestrial Laser Scanner as a Tool for Assessment of Saturation and Moisture Movement in Building Materials

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    Non Destructive Testing (NDT) is a key element of modern civil engineering. It is especially important in civil and structural engineering helping both in quality control of produced elements and technical assessments of existing structures. Existing NDT methods are being continuously improved and new methods are developed or adopted from different engineering fields. Terrestrial Laser Scanner (TLS) method which is commonly used for geodetic applications has a great potential to be successfully harnessed in civil and structural engineering. TLS can be used for remote sensing of saturation of building materials. A research programme was prepared in order to prove this concept. Specimens representing most popular European building materials were scanned using TLS. Tested specimens were in different saturation states including capillary rising saturation. The saturation assessment was based on differences of values of intensity. The concept proved to be feasible and technically realistic
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