Spectral proper orthogonal decomposition

The identification of coherent structures from experimental or numerical data is an essential task when conducting research in fluid dynamics. This typically involves the construction of an empirical mode base that appropriately captures the dominant flow structures. The most prominent candidates are the energy-ranked proper orthogonal decomposition (POD) and the frequency ranked Fourier decomposition and dynamic mode decomposition (DMD). However, these methods fail when the relevant coherent structures occur at low energies or at multiple frequencies, which is often the case. To overcome the deficit of these "rigid" approaches, we propose a new method termed Spectral Proper Orthogonal Decomposition (SPOD). It is based on classical POD and it can be applied to spatially and temporally resolved data. The new method involves an additional temporal constraint that enables a clear separation of phenomena that occur at multiple frequencies and energies. SPOD allows for a continuous shifting from the energetically optimal POD to the spectrally pure Fourier decomposition by changing a single parameter. In this article, SPOD is motivated from phenomenological considerations of the POD autocorrelation matrix and justified from dynamical system theory. The new method is further applied to three sets of PIV measurements of flows from very different engineering problems. We consider the flow of a swirl-stabilized combustor, the wake of an airfoil with a Gurney flap, and the flow field of the sweeping jet behind a fluidic oscillator. For these examples, the commonly used methods fail to assign the relevant coherent structures to single modes. The SPOD, however, achieves a proper separation of spatially and temporally coherent structures, which are either hidden in stochastic turbulent fluctuations or spread over a wide frequency range

Ny-Alesund Geodetic Observatory

In 2012 the 20-m telescope at Ny-Alesund, Svalbard, operated by the Norwegian Mapping Authority (NMA), took part in 163 out of 168 scheduled sessions of the IVS program. Since spring, all data was transferred by network, and the receiver monitoring computer was replaced by a bus-coupler. In autumn, the NMA received building permission for a new observatory from the Governor of Svalbard. The bidding process and first construction work for the infrastructure will start in 2013

In-depth rheological characterization of genetically modified xanthan-variants

Xanthan is an extensively studied viscosifying agent discovered in 1961. Acetylation and pyruvylation have a major influence on its rheological properties and the effect of these groups on the conformation and rheological properties of xanthan have been studied for decades. However, these studies rely mainly on chemical modifications and therefore the degree of pyruvylation and acetylation as well as regioselectivity of deacetylation cannot be controlled. Here, we present an in-depth rheological characterization of natural xanthan and seven xanthan-variants, with defined acetylation and pyruvylation patterns created via genetic modification of Xanthomonas campestris LMG 8031. By that approach xanthan-variants with defined acetylation and pyruvylation patterns in their most natural state due to the mild production conditions were obtained. It was possible to link the defined substituent patterns to their corresponding rheological properties to give novel structure-function relationship insights of xanthan-variants in salt-free environments and in the presence of mono- and divalent cations

Cadmium isotope fractionation in an intertidal soil induced by tidal pumping

Estuarine floodplain soils are both sinks and potential sources of toxic trace metals such as Cd. Mobilization of Cd has been identified through spatiotemporal monitoring in intertidal sediments during the last decades, but no information was yet available as to what extent these biogeochemical dynamics change the Cd isotopic composition. Cores of an Aquic Udifluvent soil from an intertidal mudflat of the Elbe River, Germany, were sub-sampled at 2 cm intervals to a depth of 40 cm corresponding to a sedimentation of about 10 years. Strong redox zonation was found in the cores, with an upper suboxic zone and a lower anoxic zone of significantly different Cd isotopy. Cadmium partitioning and pore water data determined in 1985 and 1988 using a sequential extraction procedure were reassessed to explain the variations in the δ114Cd values determined in this study. The redox conditions in the mudflat soil were found to change from suboxic (Eh 300 mV) to anoxic (Eh –100 mV) at 20 cm. This was caused by semi-diurnal flooding with oxygenated river water (tidal pumping). The δ114Cd values varied systematically with depth and were correlated with the redox profile. The intense tidal water flow caused lighter Cd isotopes to desorb more readily from the parent soil in the upper suboxic zone and to subsequently redepositing in the deeper anoxic (sulfidic) zone, where the lighter Cd mobilized from Fe/Mn oxyhydroxides was found to be scavenged in sulfidic form. Tidal advection of dissolved lighter Cd down to the anoxic zone and sulfidic reprecipitation led to a decrease in δ114Cd value of up to -0.2‰ with signals of ±0.1‰ even on a seasonal timescale. It became clear that apportioning sources using Cd isotopes would be difficult given the sensitivity of the isotope record to such early-diagenetic isotope fractionation reactions

Novel measurement system for respiratory aerosols and droplets in indoor environments

The SARS-CoV-2 pandemic has created a great demand for a better understanding of the spread of viruses in indoor environments. A novel measurement system consisting of one portable aerosol-emitting mannequin (emitter) and a number of portable aerosol-absorbing mannequins (recipients) was developed that can measure the spread of aerosols and droplets that potentially contain infectious viruses. The emission of the virus from a human is simulated by using tracer particles solved in water. The recipients inhale the aerosols and droplets and quantify the level of solved tracer particles in their artificial lungs simultaneously over time. The mobile system can be arranged in a large variety of spreading scenarios in indoor environments and allows for quantification of the infection probability due to airborne virus spreading. This study shows the accuracy of the new measurement system and its ability to compare aerosol reduction measures such as regular ventilation or the use of a room air purifier

Understanding tumor heterogeneity as functional compartments - superorganisms revisited

Compelling evidence broadens our understanding of tumors as highly heterogeneous populations derived from one common progenitor. In this review we portray various stages of tumorigenesis, tumor progression, self-seeding and metastasis in analogy to the superorganisms of insect societies to exemplify the highly complex architecture of a neoplasm as a system of functional "castes.

Balancing repair and tolerance of DNA damage caused by alkylating agents

Alkylating agents constitute a major class of frontline chemotherapeutic drugs that inflict cytotoxic DNA damage as their main mode of action, in addition to collateral mutagenic damage. Numerous cellular pathways, including direct DNA damage reversal, base excision repair (BER) and mismatch repair (MMR), respond to alkylation damage to defend against alkylation-induced cell death or mutation. However, maintaining a proper balance of activity both within and between these pathways is crucial for a favourable response of an organism to alkylating agents. Furthermore, the response of an individual to alkylating agents can vary considerably from tissue to tissue and from person to person, pointing to genetic and epigenetic mechanisms that modulate alkylating agent toxicity