Investigation and Assessment of basic Flow Field Designs for the cathodic Gas Supply in low Temperature Fuel Cells

One of the major challenges in the development of polymer electrolyte fuel cells (PEFCs) is to exploit the whole potential that inheres a given membrane electrode assembly. For this purpose, the fuel cell performance can be maximised by optimising the flow field design with regard to the intended operating point. As a prerequisite for such an optimisation, the electrochemical performance of PEFCs with various cathodic flow fields (Parallel flow, serpentine, spiral and interdigitated) has been investigated. In addition, the influence of the rib width was studied by utilising each structure with different rib widths, whereby the width and the height of the channels remain constant. The characterisation of the gas distributor structures was carried out by measuring overall polarization curves and local current density distributions by means of a segmented laboratory cell with an active area of 25 cm2. The optimum gas distributor structure strongly depends on the particular operating point. Consequently, each basic structure has to be adapted for the intended operating conditions. For example, a serpentine flow field generates the highest current densities for high air fluxes whereas an interdigitated structure is preferred for small flow rates. In the same way it can be shown that a spiral structure produces the most uniform current density distributions, whereas the current density distribution of a flow field with parallel channels is extremely inhomogeneous and becomes unsteady for higher water generation rates. The variation of the rib width has shown that all areas with a high catalytic activity are situated directly over the gas channels. In contrast, the covered areas represent only a small fraction of the global performance, whereby the general tendency is independent of the basic structure of the flow field

ICDP workshop on scientific drilling of Nam Co on the Tibetan Plateau: 1 million years of paleoenvironmental history, geomicrobiology, tectonics and paleomagnetism derived from sediments of a high-altitude lake

The Tibetan Plateau is of peculiar societal relevance as it provides freshwater from the so-called “Water Tower of Asia” to a large portion of the Asian population. However, future climate change will affect the hydrological cycle in this area. To define parameters for future climate change scenarios it is necessary to improve the knowledge about thresholds, timing, pace and intensity of past climatic changes and associated environmental impacts. Sedimentary archives reaching far back in time and spanning several glacial–interglacial cycles such as Nam Co provide the unique possibility to extract such information. In order to explore the scientific opportunities that an ICDP drilling effort at Nam Co would provide, 40 scientists from 13 countries representing various scientific disciplines met in Beijing from 22 to 24 May 2018. Besides paleoclimatic investigations, opportunities for paleomagnetic, deep biosphere, tectonic and paleobiological studies were discussed. After having explored the technical and logistical challenges and the scientific opportunities all participants agreed on the great value and need to drill this extraordinary archive, which has a sediment thickness of more than 1 km, likely covering more than 1 Ma

Inductive Freeness of Ziegler's Canonical Multiderivations for Reflection Arrangements

Let $A$ be a free hyperplane arrangement. In 1989, Ziegler showed that the restriction $A''$ of $A$ to any hyperplane endowed with the natural multiplicity is then a free multiarrangement. We initiate a study of the stronger freeness property of inductive freeness for these canonical free multiarrangements and investigate them for the underlying class of reflection arrangements. More precisely, let $A = A(W)$ be the reflection arrangement of a complex reflection group $W$. By work of Terao, each such reflection arrangement is free. Thus so is Ziegler's canonical multiplicity on the restriction $A''$ of $A$ to a hyperplane. We show that the latter is inductively free as a multiarrangement if and only if $A''$ itself is inductively free.Comment: 23 pages; v2 minor changes; final version, to appear in J. Algebr

A pathway to ultracold bosonic 23Na39K ground state molecules

We spectroscopically investigate a pathway for the conversion of 23Na39K Feshbach molecules into rovibronic ground state molecules via stimulated Raman adiabatic passage. Using photoassociation spectroscopy from the diatomic scattering threshold in the a 3Σ+ potential, we locate the resonantly mixed electronically excited intermediate states |B1Π, v=8⟩ and |c3Σ+, v=30⟩ which, due to their singlet-triplet admixture, serve as an ideal bridge between predominantly a 3Σ+ Feshbach molecules and pure X 1Σ+ ground state molecules. We investigate their hyperfine structure and present a simple model to determine the singlet-triplet coupling of these states. Using Autler-Townes spectroscopy, we locate the rovibronic ground state of the 23Na39K molecule (X1Σ+, v=0, N=0⟩) and the second rotationally excited state N = 2 to unambiguously identify the ground state. We also extract the effective transition dipole moment from the excited to the ground state. Our investigations result in a fully characterized scheme for the creation of ultracold bosonic 23Na39K ground state molecules