A century of apparent atmospheric transmission over Davos, Switzerland

Pyrheliometer measurements have been carried out at the Physikalisches-Meteorologisches Observatorium Davos from 1909 to present which results in the longest stationary direct irradiance record worldwide. A variety of different instruments and measurement scales were homogenized and adjusted to the World Radiometric Reference. Following the pyrheliometric ratioing technique, a time-series of apparent atmospheric transmission was calculated and analyzed for possible trends in column transparency over Davos. In order to assess the trend found in the transmission record, the long-term annual cycle in apparent atmospheric transmission was used to deseasonalize the daily transmission data. The trends of early brightening, dimming and brightening were localized and found to be small but highly significan

Jahn-Teller effect versus Hund's rule coupling in C60N-

We propose variational states for the ground state and the low-energy collective rotator excitations in negatively charged C60N- ions (N=1...5). The approach includes the linear electron-phonon coupling and the Coulomb interaction on the same level. The electron-phonon coupling is treated within the effective mode approximation (EMA) which yields the linear t_{1u} x H_g Jahn-Teller problem whereas the Coulomb interaction gives rise to Hund's rule coupling for N=2,3,4. The Hamiltonian has accidental SO(3) symmetry which allows an elegant formulation in terms of angular momenta. Trial states are constructed from coherent states and using projection operators onto angular momentum subspaces which results in good variational states for the complete parameter range. The evaluation of the corresponding energies is to a large extent analytical. We use the approach for a detailed analysis of the competition between Jahn-Teller effect and Hund's rule coupling, which determines the spin state for N=2,3,4. We calculate the low-spin/high-spin gap for N=2,3,4 as a function of the Hund's rule coupling constant J. We find that the experimentally measured gaps suggest a coupling constant in the range J=60-80meV. Using a finite value for J, we recalculate the ground state energies of the C60N- ions and find that the Jahn-Teller energy gain is partly counterbalanced by the Hund's rule coupling. In particular, the ground state energies for N=2,3,4 are almost equal

Simultaneous mapping of temporally-resolved blood flow velocity and oxygenation in femoral artery and vein during reactive hyperemia

<p>Abstract</p> <p>Background</p> <p>Post-occlusive hyperemia is often used as a paradigm to evaluate vascular reactivity, for example by measuring post-ischemic flow-mediated dilation, arterial blood flow or temporally resolved venous blood oxygenation (HbO₂). Here we demonstrate the feasibility of a simultaneous measurement of blood flow and HbO₂in the femoral circulation as part of a single procedure.</p> <p>Methods</p> <p>A multi-echo GRE pulse sequence was designed and implemented to collect velocity-encoded projections in addition to full-image echoes for field mapping as a means to quantify intravascular magnetic susceptibility. The method's feasibility was evaluated at 3T in a small pilot study involving two groups of healthy subjects (mean ages 26 ± 1.6 and 59 ± 7.3 years, N = 7 and 5, respectively) in terms of six parameters characterizing the time-course of reactive hyperemia and their sensitivity to differentiate age effects. The reproducibility was assessed on two of the seven young healthy subjects with three repeated measurements.</p> <p>Results</p> <p>The physiological parameters agree with those obtained with current methods that quantify either velocity or HbO₂alone. Of the six measures of vascular reactivity, one from each group was significantly different in the two subject groups (p < 0.05) even though the study was not powered to detect differences. The mean coefficient of variation (CV) from two subjects undergoing repeat scans were approximately 8% for the oximetric and the arterial velocimetric parameters in the femoral vein and artery, respectively, considerably below intersubject CVs (20 and 35%, for the young and older subject groups, respectively).</p> <p>Conclusion</p> <p>The proposed method is able quantify multiple parameters that may lead to more detailed assessment of peripheral vascular reactivity in a single cuff paradigm rather than in separate procedures as required previously, thereby improving measurement efficiency and patient comfort.</p

Hydropower production and river rehabilitation: A case study on an alpine river

Despite the numerous benefits of hydropower production, this renewable energy source can have serious negative consequences on the environment. For example, dams act as barriers for the longitudinal migration of organisms and transport of particulate matter. Accelerated siltation processes in the receiving river reduce the vertical connectivity between river and groundwater. Hydropeaks, caused by short-term changes in hydropower operation, result in a negative impact on both habitat and organisms, especially during winter months when natural discharge is low and almost constant. In this study, we report the current deficits present in the River Rhone from two different scientific perspectives - fish ecology and hydrology. Potential rehabilitation solutions in synergy with flood protection measures are discussed. We focus on the effects of hydropeaking in relation to longitudinal and vertical dimensions and discuss local river widening as a potential rehabilitation tool. The fish fauna in the Rhone is characterized by a highly unnatural structure (low diversity, impaired age distribution). A high correlation between fish biomass and monotonous morphology (poor cover availability) was established. Tracer hydrology provided further details about the reduced permeability of the riverbank, revealing a high degree of siltation with K values of about 4.7 × 10−6m s−1. Improving the hydrologic situation is therefore essential for the successful rehabilitation of the Rhone River. To this end, hydropeaks in the river reaches must be attenuated. This can be realized by a combination of different hard technical and soft operational measures such as retention reservoirs or slower up and down ramping of turbine

Amino acid and chlorin based degradation indicators in freshwater systems

Lakes cover a global area that is about 35 times smaller than the oceans, but carbon burial in lakes and oceans are on the same order of magnitude. Hence, understanding the processes for such high organic carbon burial in lacustrine systems is essential. We applied proxies typically used for marine environments including amino acid (AA) content and their nitrogen stable isotope composition to the water columns and sediments of three lakes that differ in their trophic states and depositions rates of sedimentary terrestrial organic matter. Additionally, we used carbon isotope fingerprinting of AAs to characterise their sources and fates. We show that this set of proxies tracks sources and degradation processes in eutrophic lakes with high sedimentary total organic carbon and nitrogen content. Those lakes also have a high total hydrolysable amino acid (THAA) content as well as higher pigment concentrations. While the Chlorin degradation Index (CI) showed increasing values with depth, the patterns were less consistent for the Degradation Index (DI). In general, all parameters failed to describe degradation in the most oligotrophic lake due to the very low organic carbon and nitrogen content in the sediment. We show that AAs are mostly of autochthonous origin and that AA contribute 5–45% to the organic material in plankton, POM, and sediment. Proxies based on AA for bacterial reworking (ΣV) or trophic level (TL) showed increasing values in the water column but relatively stable values in the sediments. Furthermore, we show that methanotrophic bacteria led to increased values for the bacterial reworking proxy (ΣV) and extraordinarily low δ13C AA values (−30 to −60‰).1. Introduction 2. Experimental 2.1. Sample locations and collection 2.2. Elemental and isotopic composition 2.3. Chlorin Index 2.4. Hydrolysation, derivatisation and quantification of amino acids 2.5. Compound specific stable isotope analysis of amino acids 2.6. Degradation index 2.7. Trophic level calculation 2.8. Statistical methods 3. Results 3.1. Bulk properties 3.2. Composition of total hydrolysable amino acids (THAA) 3.3. Degradation indicators 3.4. Compound specific stable nitrogen isotope analysis 3.5. Compound specific stable carbon isotope analysis 4. Discussion 4.1. Degradation indicators 4.2. Amino acids as source markers 4.3. Bacterial reworking 4.4. Trophic level 4.5. Carbon isotopes of amino acids 4.6. Implications 5. Conclusion

Non-triggered quantification of central and peripheral pulse-wave velocity

<p>Abstract</p> <p>Purpose</p> <p>Stiffening of the arteries results in increased pulse-wave velocity (PWV), the propagation velocity of the blood. Elevated aortic PWV has been shown to correlate with aging and atherosclerotic alterations. We extended a previous non-triggered projection-based cardiovascular MR method and demonstrate its feasibility by mapping the PWV of the aortic arch, thoraco-abdominal aorta and iliofemoral arteries in a cohort of healthy adults.</p> <p>Materials and Methods</p> <p>The proposed method "simultaneously" excites and collects a series of velocity-encoded projections at two arterial segments to estimate the wave-front velocity, which inherently probes the high-frequency component of the dynamic vessel wall modulus in response to oscillatory pressure waves. The regional PWVs were quantified in a small pilot study in healthy subjects (N = 10, age range 23 to 68 yrs) at 3T.</p> <p>Results</p> <p>The projection-based method successfully time-resolved regional PWVs for 8-10 cardiac cycles without gating and demonstrated the feasibility of monitoring beat-to-beat changes in PWV resulting from heart rate irregularities. For dul-slice excitation the aliasing was negligible and did not interfere with PWV quantification. The aortic arch and thoracoabdominal aorta PWV were positively correlated with age (p < 0.05), consistent with previous reports. On the other hand, the PWV of the iliofemoral arteries showed decreasing trend with age, which has been associated with the weakening of muscular arteries, a natural aging process.</p> <p>Conclusion</p> <p>The PWV map of the arterial tree from ascending aorta to femoral arteries may provide additional insight into pathophysiology of vascular aging and atherosclerosis.</p

Greenhouse gas emissions (CO2, CH4, and N2O) from several perialpine and alpine hydropower reservoirs by diffusion and loss in turbines

We investigated greenhouse gas emissions (CO2, CH4, and N2O) from reservoirs located across an altitude gradient in Switzerland. These are the first results of greenhouse gas emissions from reservoirs at high elevations in the Alps. Depth profiles were taken in 11 reservoirs located at different altitudes between the years 2003 and 2006. Diffusive trace gas emissions were calculated using surface gas concentrations, wind speeds and transfer velocities. Additionally, methane entering with the inflowing water and methane loss at the turbine was assessed for a subset of the reservoirs. All reservoirs were emitters of carbon dioxide and methane with an average of 970±340mgm−2day−1 (results only from four lowland and one subalpine reservoir) and 0.20±0.15mgm−2day−1, respectively. One reservoir (Lake Wohlen) emitted methane at a much higher rate (1.8±0.9mgm−2day−1) than the other investigated reservoirs. There was no significant difference in methane emissions across the altitude gradient, but average dissolved methane concentrations decreased with increasing elevation. Only lowland reservoirs were sources for N2O (72±22μgm−2day−1), while the subalpine and alpine reservoirs were in equilibrium with atmospheric concentrations. These results indicate reservoirs from subalpine/alpine regions to be only minor contributors of greenhouse gases to the atmosphere compared to other reservoir

Optical interconnect with densely integrated plasmonic modulator and germanium photodetector arrays

We demonstrate the first chip-to-chip interconnect utilizing a densely integrated plasmonic Mach-Zehnder modulator array operating at 3 x 10 Gbit/s. A multicore fiber provides a compact optical interface, while the receiver consists of germanium photodetectors

Optical interconnect solution with plasmonic modulator and Ge photodetector array

We report on an optical chip-to-chip interconnect solution, thereby demonstrating plasmonics as a solution for ultra-dense, high-speed short-reach communications. The interconnect comprises a densely integrated plasmonic Mach-Zehnder modulator array that is packaged with standard driving electronics. On the receiver side, a germanium photodetector array is integrated with trans-impedance amplifiers. A multicore fiber provides a compact optical interface to the array. We demonstrate 4 × 20 Gb/s on-off keying signaling with direct detection.ISSN:1041-1135ISSN:1941-017