DFT Calculations as a Tool to Analyse Quadrupole Splittings of Spin Crossover Fe(II) complexes

Density functional methods have been applied to calculate the quadrupole splitting of a series of iron(II) spin crossover complexes. Experimental and calculated values are in reasonable agreement. In one case spin-orbit coupling is necessary to explain the very small quadrupole splitting value of 0.77 mm/s at 293 K for a high-spin isomer

High-spin low-spin transition

Temperature dependent nuclear inelastic-scattering (NIS) of synchrotron radiation was applied to investigate both spin states of the spin-crossover complex [Fe(tpa)(NCS)(2)] (tpa = tris(2-pyridylmethyl)amine). A remarkable increase of the iron-ligand bond stretching upon spin crossover has unambiguously been identified by comparing the measured NIS spectra with theoretical simulations based on density-functional calculations

Student Engagement in a Team-Based Capstone Course: A Comparison of What Students Do and What Instructors Value

Student engagement is an important consideration across all levels of education. The adoption of student-centered teaching methods is an effective way to increase student engagement. Student engagement is at risk when instructor expectations and student participation in purposeful engagement activities are not aligned. Traditionally, student engagement is measured at the institutional level, which proves less than useful to instructors who wish to gauge engagement in specific courses in higher education. In this study, we sought to determine classroom level engagement in a capstone farm management course recently converted to the team-based learning format by comparing student perceptions regarding participation in engagement-specific activities with the instructors’ perceived importance of those same activities. The Classroom-Level Survey of Student Engagement (CLASSE) was utilized to collect student participation and instructor importance data. Data were examined utilizing a 2x2 quadrant analysis. Congruence between student participation frequency and instructor importance was found between 73.7% of the educational activities, while discrepancies were found on 26.3% of educational activities. Overall, students who completed the team-based learning-structured farm management course were physically and psychologically engaged in the learning environment. It is recommended that team-based learning be implemented in other courses within agricultural education to examine its utility in other contexts

Beitrag des ökologischen Landbaus zum Meeresumweltschutz

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Complexity and capacity bounds for quantum channels

We generalise some well-known graph parameters to operator systems by considering their underlying quantum channels. In particular, we introduce the quantum complexity as the dimension of the smallest co-domain Hilbert space a quantum channel requires to realise a given operator system as its non-commutative confusability graph. We describe quantum complexity as a generalised minimum semidefinite rank and, in the case of a graph operator system, as a quantum intersection number. The quantum complexity and a closely related quantum version of orthogonal rank turn out to be upper bounds for the Shannon zero-error capacity of a quantum channel, and we construct examples for which these bounds beat the best previously known general upper bound for the capacity of quantum channels, given by the quantum Lov\'asz theta number

The effects of marine nitrogen-fixing cyanobacteria on ocean biogeochemistry and climate – an Earth system model perspective

Marine nitrogen (N2) fixing cyanobacteria provide a major supply of bioavailable nitrogen to the ocean’s euphotic zone. Furthermore, cyanobacteria organisms, largely positively buoyant, absorb light at the ocean surface and thereby modify the distribution of radiative heating in the water column. In this thesis, I investigate the role of marine cyanobacteria in the Earth system – both with respect to ocean biogeochemistry and with respect to the bio-geophysical feedback by light absorption – in present and high CO2 climate conditions by using the comprehensive Earth system model of the Max Planck Institute for Meteorology (MPI-ESM). To this end, I develop and implement a parameterization of prognostic N2-fixing cyanobacteria into the HAMburg Ocean Carbon Cycle model (HAMOCC), the global ocean biogeochemistry component of MPI-ESM. Including cyanobacteria as additional phytoplankton group considerably improves the representation of N2 fixation compared to the diagnostic approach used hitherto. Cyanobacteria growth (contributing ~7% to the global primary production) and N2 fixation (with a global value of ~135 Tg N yr −1) are confined to the tropical and subtropical ocean. Temperature, phosphate and iron limitation, which in addition to fixed nitrogen deficits determine N2 fixers’ growth, lead to a decoupling of N2 fixation from the upwelling areas of nitrogen-depleted water masses. Large-scale patterns of the relative abundance of surface phosphate to nitrate are improved in the new parameterization. The prognostic growth dynamics is capable of reproducing a reasonable seasonal variability of N2 fixation and furthermore enables the consideration of the potential response of N2 fixation to changing environmental conditions, such as seawater temperature, seawater pH and changes in atmospheric dust deposition. I furthermore include the prognostic cyanobacteria in the dynamic feedback from biological light absorption on the ocean heat budget in MPI-ESM. The simulations reveal that cyanobacteria shade and hence cool the subsurface water that feeds the shallow meridional overturning cells and that is upwelled at the equator and in the eastern boundary upwelling systems. This advective process outweighs the direct local heating by cyanobacteria light absorption and results in a net surface cooling effect in large parts of the tropical and subtropical ocean by up to 0.5 K. The regional surface cooling has implications for the climate mean state, such as a strengthening (~6%) and westward shift (~3 ◦ longitude) of the Walker circulation, as well as for climate variability, such as an increase in El Niño–Southern Oscillation variability (~16%). Including the dynamic feedback from bulk phytoplankton and cyanobacteria light absorption on the ocean heat budget in MPI-ESM reduces the tropical sea surface temperature bias and improves tropical Pacific variability compared to the standard model version which applies a globally constant light attenuation depth. Under rising CO2, i.e. in a scenario in which atmospheric CO2 increases by 1% per year, both phytoplankton groups (bulk phytoplankton and cyanobacteria) are projected to decrease in the tropical and subtropical ocean. The related increase in the penetration depth of light leads to upwelling of warmer subsurface water, which amplifies tropical surface warming regionally by up to 20% under quadrupling atmospheric CO2. In an additional scenario, in which potential physiological advantages of cyanobacteria under high CO2 are considered (such as a pH-dependent growth rate, temperature adaptation, and the uptake of dissolved organic phosphorus), cyanobacteria only regionally increase their abundance. This increase counteracts the decline in water turbidity in the eastern tropical Pacific and dampens the additional warming signal of the Pacific cold tongue. This thesis indicates the relevance of including N2-fixing cyanobacteria as phytoplankton functional type in Earth system models. First, cyanobacteria growth dynamics are needed to simulate N2 fixation and its potential future evolution. Second, cyanobacteria – and changes in cyanobacteria abundance – have a regulative effect on the tropical climate system via light absorption. Cyanobacteria hence introduce additional variability in the Earth system, especially in the tropical regions, which should indeed be accounted for

Development of Collembolans after coversion towards organic farming

In Northern Germany, a diverse and complex experimental farm of the Federal Agricultural Research Centre (FAL) was set-up in 2001 covering all main aspects of organic farming. Previously, the 600 ha farm had been managed conventionally. Adjacent conventional farms were used as reference. The aim of this project was to study collembolans, microbial biomass and soil organic carbon in six organically farmed fields managed as a crop rotation of six different crops compared with an adjacent conventionally managed field. We hypothesised that the specific management in organic farming promotes soil biota. Soil samples were taken during the growing season in 2004. Collembolan abundances and microbial biomass were lower under organic management, but, generally, collembolan diversity was higher in organically farmed fields combined with a shifting in the dominance structure of the species. This result reveals that, even after three years, the soil biota is still changing with management conversion

Type I superconductivity in the Dirac semimetal PdTe2

The superconductor PdTe$_2$ was recently classified as a Type II Dirac semimetal, and advocated to be an improved platform for topological superconductivity. Here we report magnetic and transport measurements conducted to determine the nature of the superconducting phase. Surprisingly, we find that PdTe$_2$ is a Type I superconductor with $T_c = 1.64$ K and a critical field $\mu_0 H_c (0) = 13.6$ mT. Our crystals also exhibit the intermediate state as demonstrated by the differential paramagnetic effect. For $H > H_c$ we observe superconductivity of the surface sheath. This calls for a close examination of superconductivity in PdTe$_2$ in view of the presence of topological surface states.Comment: 5 page