Biodiversity Restoration and Renewable Energy from Hydropower: Conflict or Synergy?

Hydropower plants have a negative impact on biodiversity by transforming stream habitat and hydrology and thereby affecting aquatic organisms negatively. The negative effects can be mitigated by releasing water into the old river bed. This study investigates if the measure of releasing water creates costs and if ecological conditions at the old river bed contribute to such an impact. To this end, we used the cost-minimization framework in economics for deriving hypotheses. Tests were made with data from a survey to 76 hydropower plants in Sweden with questions on existence of a cost, size of the plant, type of water release from reservoirs, characteristics of the dried downstream old river bed, and official statistics on ecological status of the downstream dried segments. The results showed that 42% of the plants reported no cost, measured as impact on electricity production, from release of water into downstream old river bed. We applied logit and probit models to explain the probability of a cost. Significant results were obtained were the electricity produced and program for minimum water discharges increase the probability of loss in electricity production, but favorable ecological conditions in the old river bed decrease the probability of a cost

CD4 cell count and viral load monitoring in patients undergoing antiretroviral therapy in Uganda: cost effectiveness study

Objective To examine the cost and cost effectiveness of quarterly CD4 cell count and viral load monitoring among patients taking antiretroviral therapy (ART)

Utility of routine viral load, CD4 cell count, and clinical monitoring among adults with HIV receiving antiretroviral therapy in Uganda: randomised trial

Objective To evaluate the use of routine laboratory monitoring in terms of clinical outcomes among patients receiving antiretroviral therapy (ART) in Uganda

CO, CO2 and N2 hydrogenation reactions probed by operando x-ray photoelectron spectroscopy

Catalytic reactions are essential for generating the chemical products required by the modern society. In particular, reactions related to clean energy storage and generation as well as fertilizer production are facilitated by catalysts. However, the processes are often insufficiently understood at a mechanistic level. One of the main reasons is that a holistic investigation of heterogenous catalyst surfaces during reaction conditions requires experimental techniques that combine element specificity, surface sensitivity and can work under operando conditions. While excellent in terms of the first two criteria, x-ray photoelectron spectroscopy (XPS) has traditionally not been compatible with the high pressures and temperatures required for many catalytic reactions; a “pressure gap” opened between the obtainable conditions in the lab and the relevant conditions in a real catalytic reactor. We have built a scientific instrument, a synchrotron endstation, that addresses this issue and allows operando probing at 100x higher pressure than elsewhere. The POLARIS instrument is located at PETRA III in Hamburg. This work describes the instrumentation and the theoretical background for the technique. The main focus, however, is on the mechanistic discoveries made when operando XPS with POLARIS was applied to hydrogenation of CO, CO2 and N2 over single crystal catalysts. The surfaces examined in this work include Fe, Co, Ni, Cu-Zn, Rh and Ru. Regarding the CO hydrogenation reaction, this work describes how the Fe surfaces facilitate rapid CO dissociation, but slow adsorbate desorption. This combination results in carbide phases and a drastic accumulation of long-chain hydrocarbons. A similar behavior was noted in Ni catalysts at low temperatures, where a non-stoichiometric carbide was formed, but the hydrogenation rate of the carbide was dependent on the temperature and the partial pressure of the reactants. Co surfaces exhibit a mixture of CO and partly hydrogenated hydrocarbons, indicating a slower termination than observed on Ni, but without the drastic carburization noted for Fe. On Rh catalysts, a subset of the non-dissociated CO molecules may hydrogenate, and alkoxy intermediates co-exist with non-saturated hydrocarbons, allowing for selectivity towards oxygenated products.  For the CO2 hydrogenation reaction on Rh, the residence time of CO2 was observed to be short and the coverage of dissociated intermediates was low in the 150 mbar pressure range. However, when switching the pressure rapidly it can be shown that pressures around 2 bar increase the coverage, and reveals other adsorbates than the static pressure study. A Cu catalyst with surficial Zn was examined in ternary reaction mixtures of CO2, CO and H2. Here we noted that CO kept the Zn reduced.  In the N2 hydrogenation reaction, the rate of chemisorption and dissociation of N2 dictate two different rate limiting scenarios. On Ru the reaction is limited by the N2 dissociation and on Fe it is also limited by the hydrogenation of chemisorbed N. The significance of operando conditions is particularly manifested with regard to the hydrogen partial pressure and its interplay with the resulting adsorbate distribution.

CO, CO2 and N2 hydrogenation reactions probed by operando x-ray photoelectron spectroscopy

Catalytic reactions are essential for generating the chemical products required by the modern society. In particular, reactions related to clean energy storage and generation as well as fertilizer production are facilitated by catalysts. However, the processes are often insufficiently understood at a mechanistic level. One of the main reasons is that a holistic investigation of heterogenous catalyst surfaces during reaction conditions requires experimental techniques that combine element specificity, surface sensitivity and can work under operando conditions. While excellent in terms of the first two criteria, x-ray photoelectron spectroscopy (XPS) has traditionally not been compatible with the high pressures and temperatures required for many catalytic reactions; a “pressure gap” opened between the obtainable conditions in the lab and the relevant conditions in a real catalytic reactor. We have built a scientific instrument, a synchrotron endstation, that addresses this issue and allows operando probing at 100x higher pressure than elsewhere. The POLARIS instrument is located at PETRA III in Hamburg. This work describes the instrumentation and the theoretical background for the technique. The main focus, however, is on the mechanistic discoveries made when operando XPS with POLARIS was applied to hydrogenation of CO, CO2 and N2 over single crystal catalysts. The surfaces examined in this work include Fe, Co, Ni, Cu-Zn, Rh and Ru. Regarding the CO hydrogenation reaction, this work describes how the Fe surfaces facilitate rapid CO dissociation, but slow adsorbate desorption. This combination results in carbide phases and a drastic accumulation of long-chain hydrocarbons. A similar behavior was noted in Ni catalysts at low temperatures, where a non-stoichiometric carbide was formed, but the hydrogenation rate of the carbide was dependent on the temperature and the partial pressure of the reactants. Co surfaces exhibit a mixture of CO and partly hydrogenated hydrocarbons, indicating a slower termination than observed on Ni, but without the drastic carburization noted for Fe. On Rh catalysts, a subset of the non-dissociated CO molecules may hydrogenate, and alkoxy intermediates co-exist with non-saturated hydrocarbons, allowing for selectivity towards oxygenated products.  For the CO2 hydrogenation reaction on Rh, the residence time of CO2 was observed to be short and the coverage of dissociated intermediates was low in the 150 mbar pressure range. However, when switching the pressure rapidly it can be shown that pressures around 2 bar increase the coverage, and reveals other adsorbates than the static pressure study. A Cu catalyst with surficial Zn was examined in ternary reaction mixtures of CO2, CO and H2. Here we noted that CO kept the Zn reduced.  In the N2 hydrogenation reaction, the rate of chemisorption and dissociation of N2 dictate two different rate limiting scenarios. On Ru the reaction is limited by the N2 dissociation and on Fe it is also limited by the hydrogenation of chemisorbed N. The significance of operando conditions is particularly manifested with regard to the hydrogen partial pressure and its interplay with the resulting adsorbate distribution.

C(2)-ceramide influences the expression and insulin-mediated regulation of cyclic nucleotide phosphodiesterase 3B and lipolysis in 3T3-L1 adipocytes.

Cyclic nucleotide phosphodiesterase (PDE) 3B plays an important role in the antilipolytic action of insulin and, thereby, the release of fatty acids from adipocytes. Increased concentrations of circulating fatty acids as a result of elevated or unrestrained lipolysis cause insulin resistance. The lipolytic action of tumor necrosis factor (TNF)-alpha is thought to be one of the mechanisms by which TNF-alpha induces insulin resistance. Ceramide is the suggested second messenger of TNF-alpha action, and in this study, we used 3T3-L1 adipocytes to investigate the effects of C(2)-ceramide (a short-chain ceramide analog) on the expression and regulation of PDE3B and lipolysis. Incubation of adipocytes with 100 micromol/l C(2)-ceramide (N-acetyl-sphingosine) resulted in a time-dependent decrease of PDE3B activity, accompanied by decreased PDE3B protein expression. C(2)-ceramide, in a time- and dose-dependent manner, stimulated lipolysis, an effect that was blocked by H-89, an inhibitor of protein kinase A. These ceramide effects were prevented by 20 micromol/l troglitazone, an antidiabetic drug. In addition to downregulation of PDE3B, the antilipolytic action of insulin was decreased by ceramide treatment. These results, together with data from other studies on PDE3B and lipolysis in diabetic humans and animals, suggest a novel pathway by which ceramide induces insulin resistance. Furthermore, PDE3B is demonstrated to be a target for troglitazone action in adipocytes

A Novel Method to Maintain the Sample Position and Pressure in Differentially Pumped Systems Below the Resolution Limit of Optical Microscopy Techniques

We present a new method to maintain constant gas pressure over a sample during in situ measurements. The example shown here is a differentially pumped high-pressure X-ray photoelectron spectroscopy system, but this technique could be applied to many in situ instruments. By using the pressure of the differential stage as a feedback source to change the sample position, a new level of consistency has been achieved. Depending on the absolute value of the sample-to-aperture distance, this technique allows one to maintain the distance within several hundred nanometers, which is below the limit of typical optical microscopy systems. We show that this method is well suited to compensate for thermal drift. Thus, X-ray photoelectron spectroscopy data can be acquired continuously while the sample is heated and maintaining constant pressure over the sample. By implementing a precise manipulator feedback system, pressure variations of less than 5% were reached while the temperature was varied by 400 ℃. The system is also shown to be highly stable under significant changes in gas flow. After changing the flow by a factor of two, the pressure returned to the set value within 60 s

Microkinetic Model Fitted with a Genetic Algorithm to Experimental XPS Coverages at High Pressure – CO hydrogenation on Rh(111)

Comparisons to experiments are important when developing kinetic models based on density functional theory (DFT) calculations. The comparisons are, however, often challenging due to the assumed uncertainties in the energies from which the kinetic parameters are calculated. Here, we introduce a genetic algorithm to adjust the DFT-energies to better match experimental XPS data, using CO hydrogenation on Rh(111) as an example. The adjustments are made to adsorption energies, adsorbate-adsorbate interactions, XPS energies and peak shapes. While these parameters improve the experimental agreement considerably, the required changes to the DFT energies are relatively large, which indicates the need for refined treatments of, for example, possible surface species and reaction steps, surface inhomogeneities, or higher levels of electronic structure calculations. We propose the genetic-algorithm based method as a general tool for assessment of computational models