1,251,663 research outputs found

    Effect of (Changes in) Air Humidity on Transpiration and (Adaptation of) Stomatal Closure of Tradescantia Leaves during Water Stress

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    This paper summarises our recent research on the physiological effects of prolonged high RH during growth on stomatal function and we discuss possibilities that arise from this work for reducing postharvest quality problems in cut flowers. Chlorophyll fluorescence imaging was used to measure stomatal closure in response to desiccation of Tradescantia virginiana leaves grown under high (90%) and moderate (55%) relative humidities, or transferred between these humidities. Stomata of plants transferred from moderate RH conditions to high RH showed the same diminished closure in response to desiccation, as did stomata that developed at high RH. This response was found both when the leaves were either fully expanded or still actively expanding during the moderate RH pre-treatment. However, when leaves were grown in high RH prior to a moderate RH treatment, the reduced stomatal closure response to desiccation was only reversed in leaves (regions) which were still actively expanding during moderate RH treatment. This indicates that with respect to stomatal responses to desiccation, high RH leaf regions have only a limited capacity to adapt after transfer to moderate RH conditions. It is suggested that the diminished stomatal closure in high RH-grown plants is the result of changes in the signalling pathway for ABA-related closure induced by a prolonged period (several days) at a low ABA level. A short increase of VPD (by decreasing RH or increasing temperature) once every 2 or 3 days is probably sufficient to overcome vase life problems of cut flowers grown at high RH. Testing the acclimation ability of stomata to desiccation by transferring high RH grown plants to low VPD for just a few days would be a simply and effective screening procedure for genotypes with more adaptable stomat

    Effect of Relative Air Himidity on the Stomatal Functionality in Fully Developed Leaves

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    Several studies have shown that stomata developed under long-term high relative air humidity (RH =85%) are malfunctional, resulting in a poor control of water loss. Yet, little is known about the dynamics of stomatal adaptation to moderate RH, and the possibilities to improve or reverse the destabilized stomatal responsiveness. In this study, a reciprocal transfer experiment was conducted in climate chambers using Rosa hybrida ‘Prophyta’, grown at moderate RH (60%) or at high RH (90%). The adaptation of fully developed leaves to the new RH environment was assessed at day 0, 4, 8 and 12 after plant transfer by measuring the transpiration rate in detached leaves. Stomata fully developed at high RH had a lower closing capacity in response to a decrease in leaf Relative Water Content (RWC) (i.e. water loss was considerably high at RWC below 20%, whereas in moderate RH stomata the water loss almost ceased at 57% RWC). Furthermore, stomata developed at high RH did not become functional after 12 days of cultivation at moderate RH. Similarly, stomata developed at moderate RH and transferred to high RH for a 12 day period did not loose their ability to close in response to desiccation. This indicates that stomatal functionality is determined during leaf development, while after this period stomata have a limited capacity to adapt to new RH environment. It is concluded that stomata from fully developed rose leaves conserve their behaviour independently of the post-development humidity leve

    Rhodium Pyrazolate Complexes as Potential CVD Precursors

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    Reaction of 3,5-(CF3)(2)PzLi with [Rh(mu-Cl)(eta(2)-C2H4)(2)](2) or [Rh(mu-Cl)(PMe3)(2)](2) in Et2O gave the dinuclear complexes [Rh(eta(2)-C2H4)(2)(mu-3,5-(CF3)(2)-Pz)](2) (1) and [Rh-2(mu-Cl)(mu-3,5-(CF3)(2)-Pz) (PMe3)(4)] (2) respectively (3,5-(CF3)(2)Pz = bis-trifluoromethyl pyrazolate). Reaction of PMe3 with [Rh(COD)(mu-3,5-(CF3)(2)-Pz)](2) in toluene gave [Rh(3,5-(CF3)(2)-Pz)(PMe3)(3)] (3). Reaction of 1 and 3 in toluene (1 : 4) gave moderate yields of the dinuclear complex [Rh(PMe3)(2)(mu-3,5-(CF3)(2)-Pz)](2) (4). Reaction of 3,5-(CF3)(2)PzLi with [Rh(PMe3)(4)]Cl in Et2O gave the ionic complex [Rh(PMe3)(4)][3,5-(CF3)(2)-Pz] (5). Two of the complexes, 1 and 3, were studied for use as CVD precursors. Polycrystalline thin films of rhodium (fcc-Rh) and metastable-amorphous films of rhodium phosphide (Rh2P) were grown from 1 and 3 respectively at 170 and 130 degrees C, 0.3 mmHg in a hot wall reactor using Ar as the carrier gas (5 cc min(-1)). Thin films of amorphous rhodium and rhodium phosphide (Rh2P) were grown from 1 and 3 at 170 and 130 degrees C respectively at 0.3 mmHg in a hot wall reactor using H-2 as the carrier gas (7 cc min(-1)).Welch Foundation F-816Petroleum Research Fund 47014-ACSNSF 0741973Chemistr

    Investigating soil-water retention characteristics at high suctions using Relative Humidity control

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    A technique for controlling relative humidity (RH) is presented, which involves supplying a sealed chamber with a continuous flow of air at a computer-regulated RH. The desired value of RH is achieved by mixing dry and wet air at appropriate volumes and is measured for servo-control at three locations in the chamber with capacitive RH sensors and checked with a sensitive VAISALA sensor. The setup is capable of controlling RH steadily and continuously with a deviation of less than 0.2% RH. The technique was adopted to determine wetting soil-water retention curves (SWRC) of statically compacted London Clay, under both free-swelling and constant volume conditions. The RH within the chamber was increased in a step-wise fashion, with each step maintained until vapour equilibrium between the chamber atmosphere and the soil samples was established. Independent filter paper measurements further validate the method, while the obtained retention curves complement those available in the literature for lower ranges of suction

    Superconductivity versus structural phase transition in the closely related Bi2_{2} Rh3.5 _{3.5}S2 _{2} and Bi2_{2} Rh3 _{3}S2 _{2}

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    Single crystals of Bi2_{2} Rh3 _{3}S2 _{2} and Bi2_{2} Rh3.5 _{3.5}S2 _{2} were synthesized by solution growth and the crystal structures, thermodynamic and transport properties of both compounds were studied. In the case of Bi2_{2} Rh3 _{3}S2 _{2}, a structural first-order transition at around 165 K is identified by single crystal diffraction experiments, with clear signatures visible in resistivity, magnetization and specific heat data. No superconducting transition for Bi2_{2} Rh3 _{3}S2 _{2} was observed down to 0.5 K. In contrast, no structural phase transition at high temperature was observed for Bi2_{2} Rh3.5 _{3.5}S2 _{2}, however bulk superconductivity with a critical temperature, Tc≈T_{c}\approx 1.7 K was observed. The Sommerfeld coefficient γ\gamma\ and the Debye temperature(ΘD\varTheta_{\textrm{D}}) were found to be 9.4 mJ mol−1^{-1} K−2^{-2} and 209 K respectively for Bi2_{2} Rh3 _{3}S2 _{2}, and 22 mJ mol−1^{-1} K−2^{-2} and 196 K respectively for Bi2_{2} Rh3.5 _{3.5}S2 _{2}. Study of the specific heat in the superconducting state of Bi2_{2} Rh3.5 _{3.5}S2 _{2} suggests that Bi2_{2} Rh3.5 _{3.5}S2 _{2} is a weakly coupled, BCS superconductor.Comment: 8 pages, 11 figure

    The capability of capacitive sensors in the monitoring relative humidity in hypogeum environments

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    Hypogeum environments are characterized by high levels of relative humidity (RH). Most humidity sensors currently in use are based on the capacitive effect of the dielectric material to change according to water vapour uptake. In hypogeum environments the dielectric material can be saturated by water vapor, implying a significant error in the RH measurement. To improve the capacity of this type of humidity sensors, a modified hygrometer capacitive sensor, which uses a heating cycle to avoid the condensation, has been recently developed by Rotronic®. During four field campaigns in two different hypogea environments (the Monkey Tomb in Siena and the Mithreum of Caracalla Baths in Rome), RH was measured using the conventional capacitive sensor (CCS) and the heated capacitive sensor (HCS). The purpose of this study was to investigate the capability of HCS to detect RH variations when the environmental conditions were close to vapor saturation. Significant differences were found between the measurements of the two sensors: when RH was close to 100%, the CCS was not able to detect the RH decrease, giving only a measure of RH=100%, while HCS detected such a RH decrease. Therefore, these results encourage the use of HCS in the monitoring of RH levels in extreme humidity sites such as hypogea sites
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