Light limitation of primary production in high latitude reservoirs

International audienceTo explore the effects of vertical mixing on the primary production in a northern reservoir, a Lagrangian particle dispersion model was coupled to a 1-D reservoir model where the vertical mixing was calculated using a k-? model together with an empirically-based deep-water eddy viscosity. The primary production of each phytoplankton cell is assumed to be a function of the ambient light and not to be nutrient limited. The photoadaption follows first-order kinetics where the photoadaptive variables, a, b, and Pm, describe the coefficients of the photosynthesis-irradiance curve. The model is applied to the northern reservoir Akkajaure, which is strongly regulated with a mean and maximum depth of 30 m and 100 m respectively. Based on the release of 1000 particles (plankton), the model calculated the mean primary production of each plankton, during four different growing seasons. Vertical mixing has a substantial effect on the vertical distribution of phytoplankton and, thus, on the primary production in a reservoir. It was found that primary production was greater in a cold summer with weak stratification than in a warm summer when the reservoir was more stratified

Development and initial validation of the comprehensive HIV adherence with treatment scale

2021 Spring.Includes bibliographical references.HIV remains a significant public health concern despite decreasing rates of transmission in the U.S. (Centers for Disease Control and Prevention, 2020c). Contributing factors include low rates of treatment adherence (de Bruin et al., 2010) and high rates of comorbidities with other medical and mental health conditions (Bing et al., 2001; Gallant et al., 2017; Lerner et al., 2020). Antiretroviral therapy (ART) has significantly improved HIV health outcomes and reduced AIDS diagnoses and AIDS-related mortality (Crum et al., 2006; Glass et al., 2008; Ickovics & Meade, 2002; Paterson et al., 2000; Stone, 2001; World Health Organization, 2015). Because of ART's effectiveness, HIV is considered a chronic rather than terminal health condition for people adherent with treatment (Aberg, 2006; Swendeman, Ingram, & Rotheram- Borus, 2009). Treatment for HIV as a chronic health condition includes several pro-health behaviors in addition to ART adherence to support overall wellness. To support future research and treatment recommendations, the current study developed a measure of adherence with pro- health behavior and conducted an initial analysis of the measure's psychometric properties with a sample of 118 people living with HIV. Structural equation modeling explored relations among antecedents (personality, treatment self-efficacy, treatment information, and treatment motivation) and health outcomes of pro-health behaviors and ART adherence. Regularly assessing engagement in, as well as antecedents and outcomes of, treatment behaviors can enhance communication between providers and people living with HIV, reinforce HIV's status as a manageable chronic condition, and link people living with HIV to appropriate interventions

Social interaction anxiety and personality traits predicting engagement in risky sexual behavior

2017 Summer.Includes bibliographical references.Social anxiety disorder is a prevalent psychiatric condition, especially among adolescents (American Psychiatric Association, 2013, p. 204). Individuals with social interaction anxiety, which pertains to interpersonal exchanges with others, ruminate on perceived failures in past interactions, withdraw from or avoid social encounters, and engage in coping behaviors in response to negative feelings (Clark & Wells, 1995; Hoffman, 2007; Kashdan, 2004; Leary, 2001). While the majority of individuals with social interaction anxiety avoid risky situations, a subset engages in risky behaviors, including more frequent sexual encounters and unprotected sex (Kashdan, Elhai, & Breen, 2008; Kashdan & Hoffman, 2008; Kashdan, McKnight, Richey, & Hoffman, 2009). The personality constructs sensation seeking, emotion dysregulation, and impulsivity predict engagement in risky sexual behavior and have been suggested in previous studies to explain the relation between social interaction anxiety and risky sexual behavior (Arnold, Fletcher, & Farrow, 2002; Gullette & Lyons, 2005, 2006; Hoyle, Fejfar, & Miller, 2000; Kalichman et al., 1994; Kashdan et al., 2008; Kashdan et al., 2009; Kashdan & Hoffman, 2008; Kashdan & McKnight, 2010; Parent & Newman, 1999). Therefore, the present study hypothesized that latent classes of social interaction anxiety and personality traits would be identified that distinguish engagement in risky sexual behaviors. Finite mixture modeling was used to discern latent heterogeneous classes of social interaction anxiety and facets of sensation seeking, emotion dysregulation, impulsivity, behavioral approach, and behavioral inhibition. Risky sexual behaviors were treated as auxiliary variables. Four classes were discerned: two low social interaction anxiety classes distinguished by facets of emotion dysregulation, positive urgency, and negative urgency (Low SIAS High Urgency and Low SIAS Low Urgency) and two high social interaction anxiety classes distinguished by positive urgency, negative urgency, risk seeking, and facets of emotion dysregulation (High SIAS High Urgency and High SIAS Low Urgency). Of importance to this study were the findings that the High SIAS High Urgency class was significantly more likely to engage in all identified risky sexual behaviors than the High SIAS Low Urgency class and that the High SIAS High Urgency class did not significantly differ from the Low SIAS High Urgency and Low SIAS Low Urgency classes in engagement in risky sexual behaviors. This study extends previous findings on the heterogeneity of social interaction anxiety by identifying the effects of social interaction anxiety and personality on engagement in risky sexual behaviors

Quantitative predictions of thermodynamic hysteresis: Temperature-dependent character of the phase transition in Pd–H

The thermodynamics of phase transitions between phases that are size-mismatched but coherent differs from conventional stress-free thermodynamics. Most notably, in open systems such phase transitions are always associated with hysteresis. In spite of experimental evidence for the relevance of these effects in technologically important materials such as Pd hydride, a recipe for first-principles-based atomic-scale modeling of coherent, open systems has been lacking. Here, we develop a methodology for quantifying phase boundaries, hysteresis, and coherent interface free energies using density-functional theory, alloy cluster expansions, and Monte Carlo simulations in a constrained ensemble. We apply this approach to Pd–H and show that the phase transition changes character above approximately 400 K, occurring with an at all times spatially homogeneous hydrogen concentration, i.e., without coexistence between the two phases. Our results are consistent with experimental observations but reveal aspects of hydride formation in Pd nanoparticles that have not yet been accessible in experiment

The Goldberger-Treiman Discrepancy in SU(3)

The Goldberger-Treiman discrepancy in SU(3) is analyzed in the framework of heavy baryon chiral perturbation theory (HBChPT). It is shown that the discrepancy at leading order is entirely given by counterterms from the order p^3 Lagrangian, and that the first subleading corrections are suppressed by two powers in the HBChPT expansion. These subleading corrections include meson-loop contributions as well as counterterms from the order p^5 Lagrangian. Some one-loop contributions are calculated and found to be small. Using the three discrepancies (pi-N-N, K-N-Lambda and K-N-Sigma) which can be extracted from existing experimental data, we find that the HBChPT calculation favors the smaller g(pi-N-N) values obtained in recent partial wave analyses.Comment: 16 pages,2 figures, revte

A tale of two phase diagrams: Interplay of ordering and hydrogen uptake in Pd–Au–H

Due to their ability to reversibly absorb/desorb hydrogen without hysteresis, Pd–Au nanoalloys have been proposed as materials for hydrogen sensing. For sensing, it is important that absorption/desorption isotherms are reproducible and stable over time. A few studies have pointed to the influence of short and long range chemical order on these isotherms, but many aspects of the impact of chemical order have remained unexplored. Here, we use alloy cluster expansions to describe the thermodynamics of hydrogen in Pd–Au in a wide concentration range. We investigate how different chemical orderings, corresponding to annealing at different temperatures as well as different external pressures of hydrogen, impact the behavior of the material with focus on its hydrogen absorption/desorption isotherms. In particular, we find that a long-range ordered L12 phase is expected to form if the H2 pressure is sufficiently high. Furthermore, we construct the phase diagram at temperatures from 250 K to 500 K, showing that if full equilibrium is reached in the presence of hydrogen, phase separation can often be expected to occur, in stark contrast to the phase diagram in para-equilibrium. Our results explain the experimental observation that absorption/desorption isotherms in Pd–Au are often stable over time, but also reveal pitfalls for when this may not be the case

Computational assessment of the efficacy of halides as shape-directing agents in nanoparticle growth

We report a comprehensive study of aqueous halide adsorption on nanoparticles of gold and palladium that addresses several limitations hampering the use of atomistic modeling as a tool for understanding and improving wet-chemical synthesis and related applications. A combination of thermodynamic modeling with density functional theory (DFT) calculations and experimental data is used to predict equilibrium shapes of halide-covered nanoparticles as a function of the chemical environment. To ensure realistic and experimentally relevant results, we account for solvent effects and include a large set of vicinal surfaces, several adsorbate coverages, as well as decahedral particles. While the observed stabilization is not significant enough to result in thermodynamic stability of anisotropic shapes such as nanocubes, nonuniformity in the halide coverage indicates the possibility of obtaining such shapes as kinetic products. With regard to technical challenges, we show that inclusion of surface-solvent interactions leads to qualitative changes in the predicted shape. Furthermore, accounting for nonlocal interactions on the functional level yields a more accurate description of surface systems

The Design and Construction of a Radio Telemetry Unit for the Study of Ruminal Pressures

Many attempts have been made in the past few years to construct small implantable radio transmitters which can be used to study physiological characteristics of unrestrained animals. The success of these units has increased almost directly with the “state of the art” of transistor circuit design, and considerable heretofore unobtainable data is being collected in this manner. Most of the effort, and success, has been with transmitters for the study of heart rate, core temperature, and alimentary canal pressure. The study of bloat in ruminants is believed to be an application for which the use of such devices would be particularly suitable. A pressure sensitive transmitter placed in the rumen of an animal would allow continual but remote monitoring of the pressure while the animal is in a natural and undisturbing environment. The three primary characteristics believed necessary in a transmitter for this purpose are: (1) a size which is small enough to be given the animal orally, yet large enough to remain in the rumen; (2) a relatively long operational life which would allow observations to be conducted over an extended period of time with a minimum of harassment to the animal; and (3) a sensitivity such that observations of normal rumenal activity can be observed. This study will outline the design and construction of a unit that will record such data

Weathering rates and origin of inorganic carbon as influenced by river regulation in the boreal sub-arctic region of Sweden

International audienceMajor environmental stressors of boreal and sub-arctic rivers are hydrological changes and global warming and both factors will significantly influence the future evolution of the river chemistry in high latitudes. We tested the hypothesis whether lower concentrations of dissolved constituents observed in regulated rivers come along with lower weathering rates, though specific discharge as a major force for physical erosion and weathering is often higher in regulated river systems. In this study the river chemistry, weathering rates and related carbon dioxide consumption in two large watersheds in the sub arctic region of Sweden, one regulated river (Lule River) and one unregulated river (Kalix River), was investigated. Weathering rates of silicates in the two watersheds are shown to be different; the silicate weathering rate in Kalix River catchment is almost 30% higher than in the Lule River catchment. This is most likely a result of constructing large reservoirs in the former river valleys inundating the alluvial deposits and thus decreasing soil/water contact resulting in lower weathering rates. Furthermore, the difference observed in weathering rates between lowland regions and headwaters suggests that weathering in sub arctic boreal climates is controlled by the residence time for soil water rock interactions followed by lithology. The chemistry in the two rivers shows weathering of silicates as the origin for 68% of the inorganic carbon in the Lule River and 74% for Kalix River. The study clearly shows that river regulation significantly decreases alkalinity export to the sea because lower weathering rates gives less carbon dioxide ending up as DIC. By considering sources for inorganic carbon we here report that the inorganic carbon load that originates from respiration of organic matter in soils makes up of 30% and 35% of the total C export for the watersheds of the Kalix River and Lule River, respectively. Therefore, both the inorganic (i.e. the origin of carbon in DIC) and organic carbon load carbon must be considered when studying climate changes on the organic carbon load since effects from increased degradation of organic matter may lead to more weathering (higher production of DIC)