Leibniz University of Hanover

About: Leibniz University of Hanover is a education organization based out in Hanover, Niedersachsen, Germany. It is known for research contribution in the topics: Finite element method & Population. The organization has 14283 authors who have published 29845 publications receiving 682152 citations.

Storage and stability of organic carbon in soils as related to depth, occlusion within aggregates, and attachment to minerals

Abstract: Conceptual models suggest that stability of or- ganic carbon (OC) in soil depends on the source of plant litter, occlusion within aggregates, incorporation in organo- mineral complexes, and location within the soil profile. Den- sity fractionation is a useful tool to study the relevance of OC stabilization in aggregates and in association with min- erals, but it has rarely been applied to full soil profiles. We aim to determine factors shaping the depth profiles of phys- ically unprotected and mineral associated OC and test their relevance for OC stability across a range of European soils that vary in vegetation, soil types, parent material, and land use. At each of the 12 study sites, 10 soil cores were sam- pled to 60 cm depth and subjected to density separation. Bulk soil samples and density fractions (free light fractions - fLF, occluded light fractions - oLF, heavy fractions - HF) were analysed for OC, total nitrogen (TN), 13 C, and 1 14 C. Bulk samples were also incubated to determine CO2 evolution per g OC in the samples (specific mineralization rates) as an in- dicator for OC stability. Depth profiles of OC in the light fraction (LF-OC) matched those of roots for undisturbed grassland and forest sites, suggesting that roots are shaping the depth distribution of LF-OC. Organic C in the HF declined less with soil depth than LF-OC and roots, especially at grassland sites. The de- crease in 1 14 C (increase in age) of HF-OC with soil depth was related to soil pH as well as to dissolved OC fluxes. This indicates that dissolved OC translocation contributes to the formation of subsoil HF-OC and shapes the 1 14 C profiles. The LF at three sites were rather depleted in 14 C, indi- cating the presence of fossil material such as coal and lig- nite, probably inherited from the parent material. At the other sites, modern 1 14 C signatures and positive correlations be- tween specific mineralization rates and fLF-OC indicate the fLF is a potentially available energy and nutrient source for subsurface microorganisms throughout the profile. Declining specific mineralization rates with soil depth confirm greater stability of OC in subsoils across sites. The overall impor- tance of OC stabilization by binding to minerals was demon- strated by declining specific mineralization rates with in- creasing contributions of HF-OC to bulk soil OC, and the low 1 14 C values of HF-OC. The stability of HF-OC was greater in subsoils than in topsoils; nevertheless, a portion of HF-OC was active throughout the profile. While quanti- tatively less important than OC in the HF, consistent older ages of oLF-OC than fLF-OC suggest that occlusion of LF- OC in aggregates also contributes to OC stability in subsoils. Overall, our results indicate that association with minerals is the most important factor in stabilization of OC in soils, irre- spective of vegetation, soil type, and land use.

Effect of water on tholeiitic basalt phase equilibria: an experimental study under oxidizing conditions

Abstract: To investigate the effect of water on phase relations and compositions in a basaltic system, we performed crystallization experiments at pressures of 100, 200 and 500 MPa in a temperature range of 940 to 1,220°C using four different water contents. Depending on the water activity, the oxygen fugacity varied between 1 and 4 log units above the quartz-magnetite-fayalite buffer. Addition of water to the dry system shifts the solidus > 250°C to lower temperatures and increases the amount of melt drastically. For instance, at 1,100°C and 200 MPa, the melt fraction increases from 12.5 wt% at a water content of 1.6 wt% to 96.3% at a water content of 5 wt% in the melt. The compositions of the experimental phases also show a strong effect of water. Plagioclase is shifted to higher anorthite contents by the addition of water. Olivine and clinopyroxene show generally higher MgO/FeO ratios with added water, which could also be related to the increasing oxygen fugacity with water. Moreover, water affects the partitioning of certain elements between minerals and melts, e.g., the Ca partitioning between olivine and melt. Plagioclase shows a characteristic change in the order of crystallization with water that may help to explain the formation of wehrlites intruding the lower oceanic crust (e.g., in Oman, Macquarie Island). At 100 MPa, plagioclase crystallizes before clinopyroxene at all water contents. At pressures > 100 MPa, plagioclase crystallizes before clinopyroxene at low water contents (e.g. 3 wt%. This change in crystallization order indicates that a paragenesis typical for wehrlites (olivine–clinopyroxene–without plagioclase) is stabilized at low pressures typical of the oceanic crust only at high water contents. This opens the possibility that typical wehrlites in the oceanic crust can be formed by the fractionation and accumulation of olivine and clinopyroxene at 1,060°C and > 100 MPa in a primitive tholeiitic basaltic system containing more than 3 wt% water. The comparison of the experimental results with evolution trends calculated by the thermodynamic models “MELTS” and “Comagmat” shows that neither model predicts the experimental phase relations with sufficient accuracy.

Evaluation of quality of life after laparoscopic surgery: evidence-based guidelines of the European Association for Endoscopic Surgery.

Abstract: Measuring health-related quality of life (QoL) after surgery is essential for decision making by patients, surgeons, and payers. The aim of this consensus conference was twofold. First, it was to determine for which diseases endoscopic surgery results in better postoperative QoL than open surgery. Second, it was to recommend QoL instruments for clinical research. An expert panel selected 12 conditions in which QoL and endoscopic surgery are important. For each condition, studies comparing endoscopic and open surgery in terms of QoL were identified. The expert panel reached consensus on the relative benefits of endoscopic surgery and recommended generic and disease-specific QoL instruments for use in clinical research. Randomized trials indicate that QoL improves earlier after endoscopic than open surgery for gastroesophageal reflux disease (GERD), cholecystolithiasis, colorectal cancer, inguinal hernia, obesity (gastric bypass), and uterine disorders that require hysterectomy. For spleen, prostate, malignant kidney, benign colorectal, and benign non-GERD esophageal diseases, evidence from nonrandomized trials supports the use of laparoscopic surgery. However, many studies failed to collect long-term results, used nonvalidated questionnaires, or measured QoL components only incompletely. The following QoL instruments can be recommended: for benign esophageal and gallbladder disease, the GIQLI or the QOLRAD together with SF-36 or the PGWB; for obesity surgery, the IWQOL-Lite with the SF-36; for colorectal cancer, the FACT-C or the EORTC QLQ-C30/CR38; for inguinal and renal surgery, the VAS for pain with the SF-36 (or the EORTC QLQ-C30 in case of malignancy); and after hysterectomy, the SF-36 together with an evaluation of urinary and sexual function. Laparoscopic surgery provides better postoperative QoL in many clinical situations. Researchers would improve the quality of future studies by using validated QoL instruments such as those recommended here.

Continuous variable quantum key distribution: finite-key analysis of composable security against coherent attacks.

Abstract: We provide a security analysis for continuous variable quantum key distribution protocols based on the transmission of two-mode squeezed vacuum states measured via homodyne detection. We employ a version of the entropic uncertainty relation for smooth entropies to give a lower bound on the number of secret bits which can be extracted from a finite number of runs of the protocol. This bound is valid under general coherent attacks, and gives rise to keys which are composably secure. For comparison, we also give a lower bound valid under the assumption of collective attacks. For both scenarios, we find positive key rates using experimental parameters reachable today.

Effects of Various Resin Composite (Co)monomers and Extracts on Two Caries-associated Micro-organisms in vitro

Abstract: Previous studies have shown that extracts of various filling materials, e.g., resin composites, may influence the growth of cariogenic micro-organisms. The purpose of this study was to examine the effects of important resin composite (co)monomers (Bis-GMA, UDMA, TEGDMA, EGDMA) and extracts of two commercial dental composites with similar composition (composite A, Arabesk; composite S, Superlux) on the growth of the two cariogenic bacterial pathogens Streptococcus sobrinus and Lactobacillus acidophilus. It was found that neither the monomers Bis-GMA and UDMA, nor the comonomer EGDMA, nor the extract of composite A influenced the growth of S. sobrinus in the log phase. The comonomer TEGDMA and the extract of composite S were found to stimulate growth in the log phase, but this stimulation was not statistically significant. However, EGDMA, TEGDMA, and the extract of composite S did stimulate the total growth of S. sobrinus. In the assays with L. acidophilus, Bis-GMA, UDMA, and the extract of composite A inhibited the growth in the log phase, whereas TEGDMA stimulated it. Furthermore, EGDMA, TEGDMA, and the extract of composite S stimulated the biomass production of L. acidophilus. We conclude from our results that a release of EGDMA and TEGDMA from resin composites should be avoided due to their growth-stimulating effects on the caries-associated micro-organisms S. sobrinus and L. acidophilus.