Re-appearance of the pairing correlations at finite temperature

Rotational and deformation dependence of isovector and isoscalar pairing correlations at finite temperature are studied in an exactly solvable cranked deformed shell model Hamiltonian. It is shown that isovector pairing correlations, as expected, decrease with increasing deformation and the isoscalar pairing correlations remain constant at temperature, T=0. However, it is observed that at finite temperature both isovector and isoscalar pairing correlations are enhanced with increasing deformation, which contradict the mean-field predictions. It is also demonstrated that the pair correlations, which are quenched at T=0 and high rotational frequency re-appear at finite temperature. The changes in the individual multipole pairing fields as a function of rotation and deformation are analyzed in detail.Comment: 16 pages 6 figure

Alterations in microbial community composition with increasing fCO2: a mesocosm study in the eastern Baltic Sea

Ocean acidification resulting from the uptake of anthropogenic carbon dioxide (CO₂) by the ocean is considered a major threat to marine ecosystems. Here we examined the effects of ocean acidification on microbial community dynamics in the eastern Baltic Sea during the summer of 2012 when inorganic nitrogen and phosphorus were strongly depleted. Large-volume in situ mesocosms were employed to mimic present, future and far future CO₂ scenarios. All six groups of phytoplankton enumerated by flow cytometry ( &lt;  20 µm cell diameter) showed distinct trends in net growth and abundance with CO₂ enrichment. The picoeukaryotic phytoplankton groups Pico-I and Pico-II displayed enhanced abundances, whilst Pico-III, <i>Synechococcus</i> and the nanoeukaryotic phytoplankton groups were negatively affected by elevated fugacity of CO₂ (<i>f</i>CO₂). Specifically, the numerically dominant eukaryote, Pico-I, demonstrated increases in gross growth rate with increasing <i>f</i>CO₂ sufficient to double its abundance. The dynamics of the prokaryote community closely followed trends in total algal biomass despite differential effects of <i>f</i>CO₂ on algal groups. Similarly, viral abundances corresponded to prokaryotic host population dynamics. Viral lysis and grazing were both important in controlling microbial abundances. Overall our results point to a shift, with increasing <i>f</i>CO₂, towards a more regenerative system with production dominated by small picoeukaryotic phytoplankton.</p

Spatial distribution of intact polar lipids in North Sea surface waters: Relationship with environmental conditions and microbial community composition

We characterized and quantified the intact polar lipid (IPL) composition of the surface waters of the North Sea and investigated its relationships with environmental conditions, microbial abundances, and community composition. The total IPL pool comprised at least 600 different IPL species in seven main classes: the glycerophospholipids phosphatidylcholine (PC), phosphatidylglycerol (PG), and phosphatidylethanolamine (PE); the sulfur-bearing glycerolipid sulfoquinovosyldiacylglycerol (SQDG); and the nitrogen-bearing betaine lipids diacylglyceryl-trimethylhomoserine (DGTS), diacylglyceryl-hydroxymethyltrimethylalanine (DGTA), and diacylglyceryl-carboxy-hydroxymethylcholine (DGCC). Although no significant relationships were found between the IPL composition and environmental parameters, such as nutrient concentrations, distance-based ordination yielded distinct clusters of IPL species, which could in turn be tentatively correlated with the predominant microbial groups. SQDGs and PGs, as well as PC species containing saturated fatty acid moieties, were related to picoeukaryote abundances and PC species with polyunsaturated fatty acid (PUFA) moieties to nanoeukaryote abundances. The PEs were likely of mixed cyanobacterial-bacterial origin, whereas DGTA and DGCC species were mainly associated with cyanobacteria. DGTSs were likely derived from either pico-or nanoeukaryotes, although the DGTS species with PUFAs also showed some relationship with cyanobacterial abundances. Concentrations of the algal-derived IPLs showed strong positive correlations with chlorophyll a concentrations, indicating they may be used as biomarkers for living photosynthetic microbes. However, direct relationships between the IPLs and microbial groups were relatively weak, implying that the predominant IPLs in marine surface waters are not derived from single microbial groups and that direct inferences of microbial community compositions from IPL compositions should be considered with care

GABAergic Synapse Properties May Explain Genetic Variation in Hippocampal Network Oscillations in Mice

Cognitive ability and the properties of brain oscillation are highly heritable in humans. Genetic variation underlying oscillatory activity might give rise to differences in cognition and behavior. How genetic diversity translates into altered properties of oscillations and synchronization of neuronal activity is unknown. To address this issue, we investigated cellular and synaptic mechanisms of hippocampal fast network oscillations in eight genetically distinct inbred mouse strains. The frequency of carbachol-induced oscillations differed substantially between mouse strains. Since GABAergic inhibition sets oscillation frequency, we studied the properties of inhibitory synaptic inputs (IPSCs) received by CA3 and CA1 pyramidal cells of three mouse strains that showed the highest, lowest and intermediate frequencies of oscillations. In CA3 pyramidal cells, the frequency of rhythmic IPSC input showed the same strain differences as the frequency of field oscillations. Furthermore, IPSC decay times in both CA1 and CA3 pyramidal cells were faster in mouse strains with higher oscillation frequencies than in mouse strains with lower oscillation frequency, suggesting that differences in GABAA-receptor subunit composition exist between these strains. Indeed, gene expression of GABAA-receptor β2 (Gabrb2) and β3 (Gabrb2) subunits was higher in mouse strains with faster decay kinetics compared with mouse strains with slower decay kinetics. Hippocampal pyramidal neurons in mouse strains with higher oscillation frequencies and faster decay kinetics fired action potential at higher frequencies. These data indicate that differences in genetic background may result in different GABAA-receptor subunit expression, which affects the rhythm of pyramidal neuron firing and fast network activity through GABA synapse kinetics

Solar radiation, and solar radiation driven cycles in warming and fresh water discharge control seasonal and inter-annual phytoplankton chlorophyll a and taxonomic composition in a high Arctic fjord (Kongsfjorden, Spitsbergen)

Fjords on the west coast of Spitsbergen experience variable Arctic and Atlantic climate signals that drive seasonal and inter-annual variability of phytoplankton productivity and composition, by mechanisms that are not fully resolved. To this end, a time series (2013–2018) of Kongsfjorden (N 78�54.2, E 11�54.0) phytoplankton pigments, ocean physics, nutrient concentrations, and microbial abundances was investigated. Kongsfjorden phy- toplankton dynamics were predominantly governed by solar radiation and cycles of warming and freshwater dis- charge that caused pronounced changes in light and nutrient availability. Phytoplankton growth after the polar night commenced in March in a mixed, nutrient loaded water column, and accelerated in April after weak ther- mal stratification. Spring (weeks 10–22) showed high diatom relative abundance that ceased when silicic acid and nitrate reached limiting concentrations. Summer (weeks 23–35) was characterized by sixfold stronger stratification due to increased freshwater discharge and continued ocean heating. This caused a warm, low salinity surface layer with low nutrient concentrations. Small and diverse flagellates, together with high bacterial and viral abundances, thrived in this regenerative, N or P-limited system. Elevated late summer chlorophyll a (Chl a), and ammonium suggested increased regeneration and nutrient pulses by glacial upwelling. Fall (weeks 36–48) caused rapidly declining Chl a and increasing diatom relative abundance, which persisted throughout the polar night, causing high diatom relative abundance during spring. Despite inter-annual variability in ocean temperature and salinity we observed relatively stable seasonal phytoplankton taxonomic composition and Chl a

Isovector and isoscalar superfluid phases in rotating nuclei

The subtle interplay between the two nuclear superfluids, isovector T=1 and isoscalar T=0 phases, are investigated in an exactly soluble model. It is shown that T=1 and T=0 pair-modes decouple in the exact calculations with the T=1 pair-energy being independent of the T=0 pair-strength and vice-versa. In the rotating-field, the isoscalar correlations remain constant in contrast to the well known quenching of isovector pairing. An increase of the isoscalar (J=1, T=0) pair-field results in a delay of the bandcrossing frequency. This behaviour is shown to be present only near the N=Z line and its experimental confirmation would imply a strong signature for isoscalar pairing collectivity. The solutions of the exact model are also discussed in the Hartree-Fock-Bogoliubov approximation.Comment: 5 pages, 4 figures, submitted to PR

Experimental evidence of intrabeam scattering in a free-electron laser driver

Abstract The effect of multiple small-angle Coulomb scattering, or intrabeam scattering (IBS) is routinely observed in electron storage rings over the typical damping time scale of milliseconds. So far, IBS has not been observed in single pass electron accelerators because charge density orders of magnitude higher than in storage rings would be needed. We show that such density is now available at high brightness electron linacs for free-electron lasers (FELs). We report measurements of the beam energy spread in the FERMI linac in the presence of the microbunching instability, which are consistent with a revisited IBS model for single pass systems. We also show that neglecting the hereby demonstrated effect of IBS in the parameter range typical of seeded VUV and soft x-ray FELs, results in too conservative a facility design, or failure to realise the accessible potential performance. As an example, an optimization of the FERMI parameters driven by an experimentally benchmarked model, opens the door to the extension of stable single spectral line emission to the water window (2.3–4.4 nm), with far-reaching implications for experiments in a variety of disciplines, ranging from physics and chemistry to biology and material sciences, and including nonlinear x-ray optics based on the four-wave-mixing approach.</jats:p

Characterization and temperature dependence of Arctic Micromonas polaris viruses

Global climate change-induced warming of the Artic seas is predicted to shift the phytoplankton community towards dominance of smaller-sized species due to global warming. Yet, little is known about their viral mortality agents despite the ecological importance of viruses regulating phytoplankton host dynamics and diversity. Here we report the isolation and basic characterization of four prasinoviruses infectious to the common Arctic picophytoplankter Micromonas. We furthermore assessed how temperature influenced viral infectivity and production. Phylogenetic analysis indicated that the putative double-stranded DNA (dsDNA) Micromonas polaris viruses (MpoVs) are prasinoviruses (Phycodnaviridae) of approximately 120 nm in particle size. One MpoV showed intrinsic differences to the other three viruses, i.e., larger genome size (205 ± 2 vs. 191 ± 3 Kb), broader host range, and longer latent period (39 vs. 18 h). Temperature increase shortened the latent periods (up to 50%), increased the burst size (up to 40%), and affected viral infectivity. However, the variability in response to temperature was high for the different viruses and host strains assessed, likely affecting the Arctic picoeukaryote community structure both in the short term (seasonal cycles) and long term (global warming)

Responses of the coastal bacterial community to viral infection of the algae <i>Phaeocystis globosa</i>

The release of organic material upon algal cell lyses has a key role in structuring bacterial communities and affects the cycling of biolimiting elements in the marine environment. Here we show that already before cell lysis the leakage or excretion of organic matter by infected yet intact algal cells shaped North Sea bacterial community composition and enhanced bacterial substrate assimilation. Infected algal cultures of Phaeocystis globosa grown in coastal North Sea water contained gamma-and alphaproteobacterial phylotypes that were distinct from those in the non-infected control cultures 5 h after infection. The gammaproteobacterial population at this time mainly consisted of Alteromonas sp. cells that were attached to the infected but still intact host cells. Nano-scale secondary-ion mass spectrometry (nanoSIMS) showed similar to 20% transfer of organic matter derived from the infected C-13- and N-15-labelled P. globosa cells to Alteromonas sp. cells. Subsequent, viral lysis of P. globosa resulted in the formation of aggregates that were densely colonised by bacteria. Aggregate dissolution was observed after 2 days, which we attribute to bacteriophage-induced lysis of the attached bacteria. Isotope mass spectrometry analysis showed that 40% of the particulate C-13-organic carbon from the infected P. globosa culture was remineralized to dissolved inorganic carbon after 7 days. These findings reveal a novel role of viruses in the leakage or excretion of algal biomass upon infection, which provides an additional ecological niche for specific bacterial populations and potentially redirects carbon availability