Exploring the temporally resolved electron density evolution in EUV induced plasmas

We measured for the first time the electron density in an Extreme Ultra-Violet induced plasma. This is achieved in a low-pressure argon plasma by using a method called microwave cavity resonance spectroscopy. The measured electron density just after the EUV pulse is $2.6\cdot10^{16}$ m$^{-3}$. This is in good agreement with a theoretical prediction from photo ionization, which yields a density of $4.5\cdot10^{16}$ m$^{-3}$. After the EUV pulse the density slightly increase due to electron impact ionization. The plasma (i.e. electron density) decays in tens of microseconds.Comment: 3 pages, 4 figure

Dynamical model of the dielectric screening of conjugated polymers

A dynamical model of the dielectric screening of conjugated polymers is introduced and solved using the density matrix renormalization group method. The model consists of a line of quantized dipoles interacting with a polymer chain. The polymer is modelled by the Pariser-Parr-Pople (P-P-P) model. It is found that: (1) Compared to isolated, unscreened single chains, the screened 1Bu- exciton binding energy is typically reduced by ca. 1 eV to just over 1 eV; (2) Covalent (magnon and bi-magnon) states are very weakly screened compared to ionic (exciton) states; (3) Screening of the 1Bu- exciton is closer to the dispersion than solvation limit.Comment: 12 pages, 2 figure

The Alternative for Germany’s radicalization in historical-comparative perspective

This article chronicles the AfD’s rightward repositioning and compares it with the programmatic development of three postwar German parties on the ideological wings. By highlighting factors that tilt the balance of power away from moderate reformers towards hardliners, this comparative analysis sheds light on the conditions that lead a relatively successful party on the ideological wings, such as the AfD, to radicalize its programme. Four variables stand out: whether party hardliners take the blame for the recent election loss; whether they offer a convincing programmatic and strategic alternative to the reformers; whether changes in party composition strengthen hardliners; and whether external factors enhance their weight within the party. The essay concludes that the AfD’s radicalization was unusual, but not exceptional. It is however too early to conclude that the Federal Republic’s distinctive institutions and political culture no longer impose significant costs on parties that shift their programmes away from the centre

Dissecting magnetar variability with Bayesian hierarchical models

Neutron stars are a prime laboratory for testing physical processes under conditions of strong gravity, high density, and extreme magnetic fields. Among the zoo of neutron star phenomena, magnetars stand out for their bursting behaviour, ranging from extremely bright, rare giant flares to numerous, less energetic recurrent bursts. The exact trigger and emission mechanisms for these bursts are not known; favoured models involve either a crust fracture and subsequent energy release into the magnetosphere, or explosive reconnection of magnetic field lines. In the absence of a predictive model, understanding the physical processes responsible for magnetar burst variability is difficult. Here, we develop an empirical model that decomposes magnetar bursts into a superposition of small spike-like features with a simple functional form, where the number of model components is itself part of the inference problem. The cascades of spikes that we model might be formed by avalanches of reconnection, or crust rupture aftershocks. Using Markov Chain Monte Carlo (MCMC) sampling augmented with reversible jumps between models with different numbers of parameters, we characterise the posterior distributions of the model parameters and the number of components per burst. We relate these model parameters to physical quantities in the system, and show for the first time that the variability within a burst does not conform to predictions from ideas of self-organised criticality. We also examine how well the properties of the spikes fit the predictions of simplified cascade models for the different trigger mechanisms.Comment: accepted for publication in The Astrophysical Journal; code available at https://bitbucket.org/dhuppenkothen/magnetron, data products at http://figshare.com/articles/SGR_J1550_5418_magnetron_data/129242

LOFAR early-time search for coherent radio emission from GRB 180706A

© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.The nature of the central engines of gamma-ray bursts (GRBs) and the composition of their relativistic jets are still under debate. If the jets are Poynting flux dominated rather than baryon dominated, a coherent radio flare from magnetic re-connection events might be expected with the prompt gamma-ray emission. There are two competing models for the central engines of GRBs; a black hole or a newly formed milli-second magnetar. If the central engine is a magnetar it is predicted to produce coherent radio emission as persistent or flaring activity. In this paper, we present the deepest limits to date for this emission following LOFAR rapid response observations of GRB 180706A. No emission is detected to a 3$\sigma$ limit of 1.7 mJy beam$^{-1}$ at 144 MHz in a two-hour LOFAR observation starting 4.5 minutes after the gamma-ray trigger. A forced source extraction at the position of GRB 180706A provides a marginally positive (1 sigma) peak flux density of $1.1 \pm 0.9$ mJy. The data were time-sliced into different sets of snapshot durations to search for FRB like emission. No short duration emission was detected at the location of the GRB. We compare these results to theoretical models and discuss the implications of a non-detection.Peer reviewedFinal Accepted Versio

Effect of Cover Crops, Lime and Rock Phosphate on Maize (Zea mays L.) in an Acidic Soil of Northern Guinea Savanna of Nigeria

Phosphorus deficiency is the major constraint to maize production in acidic soil of Heipang (9°38’, 8°53’) in Northern Guinea Savanna of Nigeria. The soil is high in sesquioxides and soluble aluminum and has high phosphate sorption capacity. To address this problem, a field trial was conducted between 1996-1997 to assess the responses of six tropical cover crops and maize to lime and applied rock phosphate and to evaluate the effect of these treatments on the performance and P nutrition of succeeding maize. Results of the trial showed that planting Chamaecrista rotundifolia, Lablab purpureus, Mucuna pruriens, and maize-Chamaecrista rotundifolia intercrop reduced the leaf Al concentration of succeeding maize by more than 38%. Although none of the six cover crops significantly increased grain yields of succeeding maize, C. rotundifolia was the most consistent in improving maize performance while Glycine max produced the least performance. Concentration of Mn in the index leaves of maize was significantly higher on plots where G. max preceded maize, thus accounting for the poor performance of maize on these plots. Application of Sokoto Phosphate Rock at 30 kg ha^(-1) to cover crops produced very significant improvement in the yields of succeeding maize. While liming with 1.35 t CaO ha^(-1) in 1997 raised the soil pH value by 0.2 and significantly improved total P uptake by maize

A stretcher for the Brookhaven AGS

This paper summarizes the conceptual design of a 30 GeV Stretcher ring, which is designed to increase the capacity and the quality of the experimental physics program at the AGS. In a typical 3 second operating cycle the AGS now accomplishes two functions: accelerating the beam to full energy and then providing a slow spill on a 30 GeV flattop. These tasks consume approximately equal time. The proposed Stretcher, a dc storage ring, will take up the task of distributing the high energy beam with a continuous slow spill, making it possible for the AGS to provide beam for the program at more than twice the present repetition rate. Thus the average current delivered to the experimenters will be more than doubled, and the duty cycle of the spill will increase from the present optimum of about 40% to nearly 100%. The Stretcher will continue the gradual evolution of the AGS toward a kaon factory. At present, the AGS provides about 1 {mu}A average proton current. A Booster, now under construction, is expected to increase the current to above 4 {mu}a, and the Stretcher to about 8-10 {mu}A, an order of magnitude higher than now. 5 refs., 6 figs., 1 tab