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We investigate the interaction of strong single-cycle THz-pulses with a coherent excitonic polarization. The initial bleaching is superimposed by a splitting of the 1 s exciton resonance and eventually is accompanied by the emergence of side-bands on both the high and low energy sides of the former resonance. A quantum-mechanical many-body analysis associates these observations with the transition from excitationinduced bleaching and the regime of excitonic Rabi flopping to multi-THz-photon ionization and hence the population of states with high orbital quantum numbers. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The interaction of coherent excitons with intense, single-cycle terahertz (THz) pulses is investigated. A significant bleaching of the 1 Í-exciton resonance develops into a splitting of the absorption peak and the emergence of pronounced wings with increasing THz field strength. A quantum-mechanical many-body analysis attributes the experimental observations to a transition from excitonic Rabi flopping to multi-THz-photon ionization and the population of optically dark exciton states with high quantum numbers. [ABSTRACT FROM AUTHOR]

In a Pinus taeda L. (loblolly pine) plantation, we investigated whether the response to vapour pressure deficit ( D) of canopy average stomatal conductance ( GS) calculated from sap flux measured in upper and lower branches and main stems follows a hydraulically modelled response based on homeostasis of minimum leaf water potential ( ΨL). We tested our approach over a twofold range of leaf area index ( L; 2–4 m2 m−2) created by irrigation, fertilization, and a combination of irrigation and fertilization relative to untreated control. We found that GS scaled well from leaf-level porometery [porometry-based stomatal conductance ( gs)] to branch-estimated and main stem-estimated GS. The scaling from branch- to main stem-estimated GS required using a 45 min moving average window to extract the diurnal signal from the large high-frequency variation, and utilized a light attenuation model to weigh the contribution of upper and lower branch-estimated GS. Our analysis further indicated that, regardless of L, lower branch-estimated GS represented most of the main stem-estimated GS in this stand. We quantified the variability in both upper and lower branch-estimated GS by calculating the SD of the residuals from a moving average smoothed diurnal. A light model, which incorporated penumbral effects on vertical distribution of direct light, was employed to estimate the variability in light intensity at each canopy level in order to explain the increasing SD of both upper and lower branch-estimated GS with light. The results from the light model showed that the upper limit of the variability in individual branch-estimated GS could be attributed to incoming light, but not the variation below that upper limit. A porous medium model of water flow in trees produced a pattern of variation below the upper limit that was consistent with the observed variability in branch-estimated GS. Our results indicated that stems acted to buffer leaf- and branch-level variation and might transmit a less-variable water potential signal to the roots. [ABSTRACT FROM AUTHOR]

We investigated interannual variability of canopy transpiration per unit ground area (EC) and per unit leaf area (EL) across seven tree species in northernWisconsin over two years. These species have previously been shown to be sufficient to upscale stand-level transpiration to the landscape level during one growing season. Our objectivewas to test whether a simple plant hydraulic model could capture interannual variation in transpiration. Three species, wetland balsam fir (Abies balsamea (L.) Mill), basswood (Tilia Americana L.) and speckled alder (Alnus rugosa (DuRoi) Spreng), had no change in EC or EL between 2000 and 2001. Red pine (Pinus resinosa Ait) had a 57 and 19% increase in EC and EL, respectively, and sugar maple (Acer saccharum Marsh) had an 83 and 41% increase in EC and EL, respectively, from 2000 to 2001. Quaking aspen (Populus tremuloides Michx) had a 50 and 21% decrease in EC and EL, respectively, from 2000 to 2001 in response to complete defoliation by forest tent caterpillar (Malascoma distria Hüber) and subsequent lower total leaf area index of the reflushed foliage. White cedar (Thuja occidentalis L.) had a 20% decrease in both EC and EL caused by lowered surfacewater in wetlands in 2001 because of lower precipitation and wetland flow management. Upland A. balsamea increased EL and EC by 55 and 53%, respectively, as a result of release from light competition of the defoliated, overstory P. tremuloides.We hypothesized that regardless of different drivers of interannual variability in EC and EL, minimum leaf water potential would be regulated at the same value. Minimum midday water potentials were consistent over the two years within each of the seven species despite large changes in transpiration between years. This regulation was independently verified by the exponential saturation between daily EC and vapor pressure deficit (D) and the tradeoff between a reference canopy stomatal conductance (GS) and the sensitivity of GS to D, indicating that trees with high GS must decrease GS in response to atmospheric drought faster than trees with low GS. Our results show that models of forest canopy transpiration can be simplified by incorporating GS regulation of minimum leaf water potential for isohydric species. [ABSTRACT FROM AUTHOR]

Fertilized (F) and irrigated and fertilized (IF) stands of Pinus taeda L. produced twice the leaf area index of irrigated (I) and control (C) stands. Based on sap flux-scaled mean stomatal conductance (GS), we found that stomatal conductance in F was half that in other treatments. During the growing season, GS was related to vapor pressure deficit (D) and soil moisture. During the cooler season, soil moisture was high and light accompanied D in controlling GS. Under all conditions and treatments, the rate of decrease in GS with D was proportional to GS at low D (= 1 kPa). We evaluated whether GS can be used as an input to growth models and used a simple growth model (3-PG), which also predicts stand transpiration (EC), to compare with direct EC measurements in the four stands. Model predictions of monthly EC based on Penman-Montieth equation parameterized with maximum GS (GSmax) estimated under highest "native" soil moisture (0.07 m³·m-3) produced long-term values within 10% of measured EC. When the model was parameterized with GSmax estimated under experimentally raised soil moisture, or with porometrically measured conductance, EC values were consistently overpredicted from 12 to 33%. Thus, sap-flux scaled mean canopy stomatal conductance obtained under non limiting light conditions, low D, and highest native soil moisture, is the most appropriate parameter value for certain single-leaf type of models. [ABSTRACT FROM AUTHOR]

ABSTRACT We investigated the hydraulic consequences of a major decrease in root-to-leaf area ratio (AR:AL) caused by nutrient amendments to 15-year-old Pinus taeda L. stands on sandy soil. In theory, such a reduction in AR:AL should compromise the trees’ ability to extract water from drying sand. Under equally high soil moisture, canopy stomatal conductance (GS) of fertilized trees (F) was 50% that of irrigated/fertilized trees (IF), irrigated trees (I), and untreated control trees (C). As predicted from theory, F trees also decreased their stomatal sensitivity to vapour pressure deficit by 50%. The lower GS in F was associated with 50% reduction in leaf-specific hydraulic conductance (KL) compared with other treatments. The lower KL in F was in turn a result of a higher leaf area per sapwood area and a lower specific conductivity (conducting efficiency) of the plant and its root xylem. The root xylem of F trees was also 50% more resistant to cavitation than the other treatments. A transport model predicted that the lower AR:AL in IF trees resulted in a considerably restricted ability to extract water during drought. However, this deficiency was not exposed because irrigation minimized drought. In contrast, the lower AR:AL in F trees caused only a limited restriction in water extraction during drought owing to the more cavitation resistant root xylem in this treatment. In both fertilized treatments, approximate safety margins from predicted hydraulic failure were minimal suggesting increased vulnerability to drought-induced dieback compared with non-fertilized trees. However, IF trees are likely to be so affected even under a mild drought if irrigation is withheld. [ABSTRACT FROM AUTHOR]

Chlorophyll a (Chl a) has an asymmetrical molecular organization, which dictates its orientation and the location of the pigment in the mature photosynthetic apparatus. Although Chl a fluorescence (ChlF) is widely accepted as a proxy for plant photosynthetic performance under countless stress conditions and across species, a mechanistic understanding of this causality is missing. Since water plays a much greater role than solvent for the photosynthetic machinery, elucidating its influence on Chl a may explain the reliable reflection of plant stress response in the ChlF signal. We examine the effect of hydration from well-watered to lethal drought on ChlF imagery results across morphologically diverse species to begin testing the impact of molecular scale hydration of Chl a on ChlF. Our results support a conceptual model where water is an integral part of the photosystems' structure and directly influences Chl a behavior leading to changes in the energy partitioning and ultimately in ChlF. [ABSTRACT FROM AUTHOR]

Abstract Forest management presents challenges to accurate prediction of water and carbon exchange between the land surface and atmosphere, due to its alteration of forest structure and composition. We examined how forest species types in northern Wisconsin affect landscape scale water fluxes predicted from models driven by remotely sensed forest classification. A site-specific classification was developed for the study site. Using this information and a digital soils database produced for the site we identified four key forest stand types: red pine, northern hardwoods, aspen, and forested wetland. Within these stand types, 64 trees representing 7 species were continuously monitored with sap flux sensors. Scaled stand-level transpiration from sap flux was combined with a two-source soil evaporation model and then applied over a 2.5 km × 3.0 km area around the WLEF AmeriFlux tower (Park Falls, Wisconsin) to estimate evapotranspiration. Water flux data at the tower was used as a check against these estimates. Then, experiments were conducted to determine the effects of aggregating vegetation types to International Geosphere– Biosphere Program (IGBP) level on water flux predictions. Taxonomic aggregation resulting in loss of species level information significantly altered landscape water flux predictions. However, daily water fluxes were not significantly affected by spatial aggregation when forested wetland evaporation was included. The results demonstrate the importance of aspen, which has a higher transpiration rate per unit leaf area than other forest species. However, more significant uncertainty results from not including forested wetland with its high rates of evaporation during wet summers. [ABSTRACT FROM AUTHOR]

This paper discusses recent studies involving time-resolved optical and terahertz (THz) fields in the linear and nonlinear regime. An overview of the microscopic modeling scheme is presented and applied to analyze a variety of experimental results. The examples include coherent excitons in weak and strong THz fields, Rabi splitting and ionization of intra-excitonic transitions, THz studies in semiconductor microcavities, and the THz manipulation of excitonic transitions. [ABSTRACT FROM AUTHOR]

We use terahertz pulses to induce resonant transitions between the eigenstates of optically generated exciton populations in a high-quality semiconductor quantum well sample. Monitoring the excitonic photoluminescence, we observe transient quenching of the 1s exciton emission, which we attribute to the terahertz-induced 1s-to-2p excitation. Simultaneously, a pronounced enhancement of the 2s exciton emission is observed, despite the 1s-to-2s transition being dipole forbidden. A microscopic many-body theory explains the experimental observations as a Coulomb-scattering mixing of the 2s and 2p states, yielding an effective terahertz transition between the 1s and 2s populations. [ABSTRACT FROM AUTHOR]

BACKGROUND: Mental Health Nurses working in secure environments with patients suffering from serious mental illness have been shown to be at risk of clinical burnout syndrome, this can have adverse effects both on the nurses' health and the standards of care that they deliver. AIM: To evaluate the effect of Psychosocial Intervention Training (PSI) on the knowledge, attitudes and levels of clinical burnout in a group of forensic mental health nurses. DESIGN: Baseline assessments of knowledge, attitude and burnout were completed by asking a group of 33 nurses working in a medium secure psychiatric unit to complete questionnaires. Twenty of the nurses volunteered to be included in a PSI training course and were randomly allocated either to receive the training or to a waiting list control group. The duration of the training was 6 months and on completion subjects in the experimental and control group completed the questionnaires again. RESULTS: Staff in the experimental group showed significant improvements in their knowledge and attitudes about serious mental illness and a significant decrease in burnout rates, whilst staff in the control group showed a small but nonsignificant improvement in knowledge and attitudes, and increase in burnout. CONCLUSION: The findings suggest that providing forensic mental health nurses with a better understanding of serious mental illness and training them in a broader range of interventions, helps them to be more positive in their attitudes towards the clients that they work with and experience less negative effects of stress resulting from their caring role. The implications of this study for clinical practice and future research will be discussed. [ABSTRACT FROM AUTHOR]

ABSTRACTResponses of stomatal conductance (gs) to increasing vapour pressure deficit (D) generally follow an exponential decrease described equally well by several empirical functions. However, the magnitude of the decrease – the stomatal sensitivity – varies considerably both within and between species. Here we analysed data from a variety of sources employing both porometric and sap flux estimates of gs to evaluate the hypothesis that stomatal sensitivity is proportional to the magnitude of gs at low D (≤ 1 kPa). To test this relationship we used the function gs = gsref – m · lnD where m is the stomatal sensitivity and gsref = gs at D = 1 kPa. Regardless of species or methodology, m was highly correlated with gsref (average r2 = 0·75) with a slope of approximately 0·6. We demonstrate that this empirical slope is consistent with the theoretical slope derived from a simple hydraulic model that assumes stomatal regulation of leaf water potential. The theoretical slope is robust to deviations from underlying assumptions and variation in model parameters. The relationships within and among species are close to theoretical predictions, regardless of whether the analysis is based on porometric measurements of gs in relation to leaf-surface D (Ds), or on sap flux-based stomatal conductance of whole trees (GSi), or stand-level stomatal conductance (GS) in relation to D. Thus, individuals, species, and stands with high stomatal conductance at low D show a greater sensitivity to D, as required by the role of stomata in regulating leaf water potential. [ABSTRACT FROM AUTHOR]