Bertelsmann Transformation Index 2009: Political Management in International Comparison

Gradual processes of democratic and economic change are just as important as momentous events in the history of states and their citizens. Few events in international politics evoke as much euphoria and hopes for the future as the fall of an authoritarian regime or the sudden move to reform

Cores in warm dark matter haloes: a Catch 22 problem

The free streaming of warm dark matter particles dampens the fluctuation spectrum, flattens the mass function of haloes and imprints a fine grained phase density limit for dark matter structures. The phase space density limit is expected to imprint a constant density core at the halo center on the contrary to what happens for cold dark matter. We explore these effects using high resolution simulations of structure formation in different warm dark matter scenarios. We find that the size of the core we obtain in simulated haloes is in good agreement with theoretical expectations based on Liouville's theorem. However, our simulations show that in order to create a significant core, (r_c~1 kpc), in a dwarf galaxy (M~1e10 Msun), a thermal candidate with a mass as low as 0.1 keV is required. This would fully prevent the formation of the dwarf galaxy in the first place. For candidates satisfying large scale structure constrains (m_wdm larger than 1-2 keV) the expected size of the core is of the order of 10 (20) pc for a dark matter halo with a mass of 1e10 (1e8) Msun. We conclude that "standard" warm dark matter is not viable solution for explaining the presence of cored density profiles in low mass galaxies.Comment: 9 pages, 8 figures, new theory section, fig 8 updated, conclusions unchanged, accepted for publication on MNRA

Repeated PTZ Treatment at 25-Day Intervals Leads to a Highly Efficient Accumulation of Doublecortin in the Dorsal Hippocampus of Rats

BACKGROUND: Neurogenesis persists throughout life in the adult mammalian brain. Because neurogenesis can only be assessed in postmortem tissue, its functional significance remains undetermined, and identifying an in vivo correlate of neurogenesis has become an important goal. By studying pentylenetetrazole-induced brain stimulation in a rat model of kindling we accidentally discovered that 25±1 days periodic stimulation of Sprague-Dawley rats led to a highly efficient increase in seizure susceptibility. METHODOLOGY/PRINCIPAL FINDINGS: By EEG, RT-PCR, western blotting and immunohistochemistry, we show that repeated convulsive seizures with a periodicity of 25±1 days led to an enrichment of newly generated neurons, that were BrdU-positive in the dentate gyrus at day 25±1 post-seizure. At the same time, there was a massive increase in the number of neurons expressing the migratory marker, doublecortin, at the boundary between the granule cell layer and the polymorphic layer in the dorsal hippocampus. Some of these migrating neurons were also positive for NeuN, a marker for adult neurons. CONCLUSION/SIGNIFICANCE: Our results suggest that the increased susceptibility to seizure at day 25±1 post-treatment is coincident with a critical time required for newborn neurons to differentiate and integrate into the existing hippocampal network, and outlines the importance of the dorsal hippocampus for seizure-related neurogenesis. This model can be used as an in vivo correlate of neurogenesis to study basic questions related to neurogenesis and to the neurogenic mechanisms that contribute to the development of epilepsy

26th Annual Computational Neuroscience Meeting (CNS*2017): Part 3 - Meeting Abstracts - Antwerp, Belgium. 15–20 July 2017

This work was produced as part of the activities of FAPESP Research,\ud Disseminations and Innovation Center for Neuromathematics (grant\ud 2013/07699-0, S. Paulo Research Foundation). NLK is supported by a\ud FAPESP postdoctoral fellowship (grant 2016/03855-5). ACR is partially\ud supported by a CNPq fellowship (grant 306251/2014-0)

Aus dem Tagebuch eines Dorpater Studenten : geschrieben in den Jahren 1809 und 1810

http://www.ester.ee/record=b3788589~S1*es

Chain-End Effects on Supramolecular Poly(ethylene glycol) Polymers

In this work we present a fundamental analysis based on small-angle scattering, linear rheology and differential scanning calorimetry (DSC) experiments of the role of different hydrogen bonding (H-bonding) types on the structure and dynamics of chain-end modified poly(ethylene glycol) (PEG) in bulk. As such bifunctional PEG with a molar mass below the entanglement mass Me is symmetrically end-functionalized with three different hydrogen bonding (H-bonding) groups: thymine-1-acetic acid (thy), diamino-triazine (dat) and 2-ureido-4[1H]-pyrimidinone (upy). A linear block copolymer structure and a Newtonian-like dynamics is observed for PEG-thy/dat while results for PEG-upy structure and dynamics reveal a sphere and a network-like behavior, respectively. These observations are concomitant with an increase of the Flory–Huggins interaction parameter from PEG-thy/dat to PEG-upy that is used to quantify the difference between the H-bonding types. The upy association into spherical clusters is established by the Percus–Yevick approximation that models the inter-particle structure factor for PEG-upy. Moreover, the viscosity study reveals for PEG-upy a shear thickening behavior interpreted in terms of the free path model and related to the time for PEG-upy to dissociate from the upy clusters, seen as virtual crosslinks of the formed network. Moreover, a second relaxation time of different nature is also obtained from the complex shear modulus measurements of PEG-upy by the inverse of the angular frequency where G’ and G’’ crosses from the network-like to glass-like transition relaxation time, which is related to the segmental friction of PEG-upy polymeric network strands. In fact, not only do PEG-thy/dat and PEG-upy have different viscoelastic properties, but the relaxation times found for PEG-upy are much slower than the ones for PEG-thy/dat. However, the activation energy related to the association dynamics is very similar for both PEG-thy/dat and PEG-upy. Concerning the segmental dynamics, the glass transition temperature obtained from both rheological and calorimetric analysis is similar and increases for PEG-upy while for PEG-thy/dat is almost independent of association behavior. Our results show how supramolecular PEG properties vary by modifying the H-bonding association type and changing the molecular Flory–Huggins interaction parameter, which can be further explored for possible application

Influence of Polymer Polarity and Association Strength on the Properties of Poly(alkyl ether)-Based Supramolecular Melts

The present work focuses on the impact of polymer polarity and hydrogen-bonding (H-bonding) end groups association strength on the structure and dynamics of poly(alkyl ether)-based supramolecular model polymers studied by means of small angle scattering (SAS), rheology, dielectric relaxation spectroscopy (DRS), and differential scanning calorimetry (DSC). These consist of poly (propylene oxide) (PPO) or poly(ethylene oxide) (PEO) backbone that self assembly in the bulk via hydrogen bonding (H-bonding). Diaminotriazine (DAT) and thymine-1-acetic acid (THY) as well as 2-ureido-4[1H]-pyrimidinone (UPY) are the H-bonding end groups of choice. Both PPO and PEO bearing either DAT or THY as end groups associate into linear chains, but PPO-THY/DAT forms longer chains in comparison with PEO-THY/DAT. The lower polarity of the backbone results in stronger associations for the same end groups. However, the temperature dependence of the association/dissociation lifetimes for this H-bonding type is independent of the different main chain polarity as these breaking times do not exceed the rouse chain dynamics as expected within the Cates model. PPO-UPY forms a transient network characterized by the interplay between small transient bonds controlled by the characteristic times of association/dissociation between pairs of UPY groups involving probably just two ends, revealed by the similar dielectric spectra with PPO backbone, and a more stable bond type of associate that forms phase separated UPY clusters. The latter are responsible for the physical cross-links in the network and result in the rubbery-like plateau of the rheological spectra. PPO-UPY has similar structure to PEO-UPY, as validated by small angle scattering, but the UPY detachment times in the clusters are longer for PEO-UPY than for PPO-UPY, though the activation energies are very close and match the typical energy barrier specifically imposed by the hydrogen bonds. Moreover, while the segmental relaxation times and the glass transition temperature (Tg) of PPO-UPY is similar to PPO, PEO-UPY has the highest Tg value and a much slower segmental relaxation as compared to PEO and PPO based supramolecular polymers. This seems to indicate that the H bonding association dynamics of the UPY groups is strongly influenced by the main chain polarity that play a fundamental role in defining the time scale of the association process