Capture numbers and islands size distributions in models of submonolayer surface growth

The capture numbers entering the rate equations (RE) for submonolayer film growth are determined from extensive kinetic Monte Carlo (KMC) simulations for simple representative growth models yielding point, compact, and fractal island morphologies. The full dependence of the capture numbers on island size, and on both the coverage and the D/F ratio between the adatom diffusion coefficient D and deposition rate F is determined. Based on this information, the RE are solved to give the RE island size distribution (RE-ISD). The RE-ISDs are shown to agree well with the corresponding KMC-ISDs for all island morphologies. For compact morphologies, however, this agreement is only present for coverages smaller than about 5% due to a significantly increased coalescence rate compared to fractal morphologies. As found earlier, the scaled KMC-ISDs as a function of scaled island size approach, for fixed coverage, a limiting curve for D/F going to infinity. Our findings provide evidence that the limiting curve is independent of the coverage for point islands, while the results for compact and fractal island morphologies indicate a dependence on the coverage.Comment: 13 pages, 12 figure

SUSY-QCD corrections in the squark-gluino sector

A status report is given of the calculations of next-to-leading-order ($N=1$) supersymmetric QCD corrections to the production of squarks and gluinos in $p\bar{p}/pp$ collisions. The implementation of these SUSY-QCD corrections leads to more stable theoretical predictions and to a substantial increase of the production cross-sections. In addition we give a discussion of the use of the $\overline{MS}$ scheme for renormalizing the coupling constants in the QCD sector of ($N=1$) supersymmetric theories.Comment: 6 two-column pages, tar'ed gzip'ed uuencoded files, LaTeX, 7 Encapsulated Postscript figures, uses epsfig and espcrc2. To appear in the proceedings of the 1996 Zeuthen Workshop on Elementary Particle Theory: "QCD and QED in Higher Orders", J.Bl\"umlein, F.Jegerlehner, and T.Riemann eds. Complete postscript file available at http://rulgm4.LeidenUniv.nl/preprints.htm

Island size distributions in submonolayer growth: successful prediction by mean field theory with coverage dependent capture numbers

We show that mean-field rate equations for submonolayer growth can successfully predict island size distributions in the pre-coalescence regime if the full dependence of capture numbers on both the island size and the coverage is taken into account. This is demonstrated by extensive Kinetic Monte Carlo simulations for a growth kinetics with hit and stick aggregation. A detailed analysis of the capture numbers reveals a nonlinear dependence on the island size for small islands. This nonlinearity turns out to be crucial for the successful prediction of the island size distribution and renders an analytical treatment based on a continuum limit of the mean-field rate equations difficult.Comment: 4 pages, 4 figue

Sustained enhancement of photosynthesis in mature deciduous forest trees after 8years of free air CO2 enrichment

Carbon uptake by forests constitutes half of the planet's terrestrial net primary production; therefore, photosynthetic responses of trees to rising atmospheric CO2 are critical to understanding the future global carbon cycle. At the Swiss Canopy Crane, we investigated gas exchange characteristics and leaf traits in five deciduous tree species during their eighth growing season under free air carbon dioxide enrichment in a 35-m tall, ca. 100-year-old mixed forest. Net photosynthesis of upper-canopy foliage was 48% (July) and 42% (September) higher in CO2-enriched trees and showed no sign of down-regulation. Elevated CO2 had no effect on carboxylation efficiency (V cmax) or maximal electron transport (J max) driving ribulose-1,5-bisphosphate (RuBP) regeneration. CO2 enrichment improved nitrogen use efficiency, but did not affect leaf nitrogen (N) concentration, leaf thickness or specific leaf area except for one species. Non-structural carbohydrates accumulated more strongly in leaves grown under elevated CO2 (largely driven by Quercus). Because leaf area index did not change, the CO2-driven stimulation of photosynthesis in these trees may persist in the upper canopy under future atmospheric CO2 concentrations without reductions in photosynthetic capacity. However, given the lack of growth stimulation, the fate of the additionally assimilated carbon remains uncertai

Not All Doom and Gloom: How Energy-Intensive and Temporally Flexible Data Center Applications May Actually Promote Renewable Energy Sources

To achieve a sustainable energy system, a further increase in electricity generation from renewable energy sources (RES) is imperative. However, the development and implementation of RES entail various challenges, e.g., dealing with grid stability issues due to RES’ intermittency. Correspondingly, increasingly volatile and even negative electricity prices question the economic viability of RES-plants. To address these challenges, this paper analyzes how the integration of an RES-plant and a computationally intensive, energy-consuming data center (DC) can promote investments in RES-plants. An optimization model is developed that calculates the net present value (NPV) of an integrated energy system (IES) comprising an RES-plant and a DC, where the DC may directly consume electricity from the RES-plant. To gain applicable knowledge, this paper evaluates the developed model by means of two use-cases with real-world data, namely AWS computing instances for training Machine Learning algorithms and Bitcoin mining as relevant DC applications. The results illustrate that for both cases the NPV of the IES compared to a stand-alone RES-plant increases, which may lead to a promotion of RES-plants. The evaluation also finds that the IES may be able to provide significant energy flexibility that can be used to stabilize the electricity grid. Finally, the IES may also help to reduce the carbon-footprint of new energy-intensive DC applications by directly consuming electricity from RES-plants

Uptake and fecal excretion of Coxiella burnetii by Ixodes ricinus and Dermacentor marginatus ticks

Background: The bacterium Coxiella burnetii is the etiological agent of Q fever and is mainly transmitted via inhalation of infectious aerosols. DNA of C. burnetii is frequently detected in ticks, but the role of ticks as vectors in the epidemiology of this agent is still controversial. In this study, Ixodes ricinus and Dermacentor marginatus adults as well as I. ricinus nymphs were fed on blood spiked with C. burnetii in order to study the fate of the bacterium within putative tick vectors. Methods: Blood-feeding experiments were performed in vitro in silicone-membrane based feeding units. The uptake, fecal excretion and transstadial transmission of C. burnetii was examined by quantitative real-time PCR as well as cultivation of feces and crushed tick filtrates in L-929 mouse fibroblast cells and cell-free culture medium. Results: Ticks successfully fed in the feeding system with engorgement rates ranging from 29% (D. marginatus) to 64% (I. ricinus adults). Coxiella burnetii DNA was detected in the feces of both tick species during and after feeding on blood containing 105 or 106 genomic equivalents per ml blood (GE/ml), but not when fed on blood containing only 104 GE/ml. Isolation and cultivation demonstrated the infectivity of C. burnetii in shed feces. In 25% of the I. ricinus nymphs feeding on inoculated blood, a transstadial transmission to the adult stage was detected. Females that molted from nymphs fed on inoculated blood excreted C. burnetii of up to 106 genomic equivalents per mg of feces. Conclusions: These findings show that transstadial transmission of C. burnetii occurs in I. ricinus and confirm that I. ricinus is a potential vector for Q fever. Transmission from both tick species might occur by inhalation of feces containing high amounts of viable C. burnetii rather than via tick bites

Reacting to Perceived Overqualification: Uniting Strain-Based and Self-Regulatory Adjustment Reactions and the Moderating Role of Formal Work Arrangements

Thus far, research on perceived overqualification has focused on either maladaptive, strain-based versus more adaptive, self-regulatory reactions in isolation. Following person-environment fit theory, we seek to advance this one-sided focus by uniting both types of adjustment reactions and to consider their implications for perceived person-job fit, and performance and wellbeing outcomes. In line with theory, we also examine contextual boundary conditions in the form of indicators of formal work arrangements (i.e., permanent vs. temporary employment contract and job tenure). Utilizing three-wave data from 453 employees, we found that perceived overqualification indirectly and sequentially related to decreases in task performance, organizational citizenship behavior and job satisfaction via anger toward employment situation and lower levels of perceived person-job fit-thus reflecting the strain-based pathway. For the self-regulatory pathway, findings did not align with our initial proposition that the positive relationship between perceived overqualification and work organization (a form of structural job crafting whereby employees improve their work processes) would be weaker among temporary employees and those with longer tenure. Instead, having a temporary employment contract or having longer job tenure resulted in a negative relationship between perceived overqualification and work organization, which further contributed to a decrease in performance and satisfaction via lower levels of perceived person-job fit. Our study highlights the demotivating role of a temporary employment contract and long job tenure for overqualified employees to reorganize their work. In discussing our findings, we point to the importance of job stage and develop recommendations for managing overqualified employees