Functional renormalization group approach to neutron matter

The chiral nucleon-meson model, previously applied to systems with equal number of neutrons and protons, is extended to asymmetric nuclear matter. Fluctuations are included in the framework of the functional renormalization group. The equation of state for pure neutron matter is studied and compared to recent advanced many-body calculations. The chiral condensate in neutron matter is computed as a function of baryon density. It is found that, once fluctuations are incorporated, the chiral restoration transition for pure neutron matter is shifted to high densities, much beyond three times the density of normal nuclear matter.Comment: 5 pages, 4 figures, to appear in Phys. Lett.

Comparing and contrasting traditional membrane bioreactor models with novel ones based on time series analysis

Copyright @ 2013 MDPI AGThis article has been made available through the Brunel Open Access Publishing Fund.The computer modelling and simulation of wastewater treatment plant and their specific technologies, such as membrane bioreactors (MBRs), are becoming increasingly useful to consultant engineers when designing, upgrading, retrofitting, operating and controlling these plant. This research uses traditional phenomenological mechanistic models based on MBR filtration and biochemical processes to measure the effectiveness of alternative and novel time series models based upon input–output system identification methods. Both model types are calibrated and validated using similar plant layouts and data sets derived for this purpose. Results prove that although both approaches have their advantages, they also have specific disadvantages as well. In conclusion, the MBR plant designer and/or operator who wishes to use good quality, calibrated models to gain a better understanding of their process, should carefully consider which model type is selected based upon on what their initial modelling objectives are. Each situation usually proves unique.This article is made available through the Brunel Open Access Publishing Fund

Penumbral micro-jets at high spatial and temporal resolution

Sunspot observations in chromospheric spectral lines have revealed the existence of short-lived linear bright transients, commonly referred to as penumbral micro-jets (PMJs). Details on the origin and physical nature of PMJs are to large extend still unkown. We aim to characterize the dynamical nature of PMJs to provide guidance for future modelling efforts. We analyze high spatial (0.1 arcsec) and temporal resolution (1 s) Ca II H filtergram (0.1 nm bandwidth) observations of a sunspot obtained on two consecutive days with the Swedish 1-m Solar Telescope. We find that PMJs appear to be the rapid brightening of an already existing (faint) fibril. The rapid brightening is the fast increase (typically less than 10 s) in intensity over significant length (several 100s of km) of the existing fibril. For most PMJs, we cannot identify a clear root or source from where the brightening appears to originate. After the fast onset, about half of the PMJs have a top that is moving with an apparent velocity between 5 and 14 km/s, most of them upwards. For the other PMJs, there is no significant motion of the top. For about a third of the PMJs we observe a splitting into two parallel and co-evolving linear features during the later phases of the lifetime of the PMJ. We conclude that mass flows can play only limited role in the onset phase of PMJs and that it is more likely that we see the effect of a fast heating front.Comment: Accepted for publication in Astronomy & Astrophysics. Movies are available at http://folk.uio.no/rouppe/pmj_highcadence

Microjets in the penumbra of a sunspot

Penumbral Microjets (PMJs) are short-lived jets found in the penumbra of sunspots, first observed in wide-band Ca H-line observations as localized brightenings, and are thought to be caused by magnetic reconnection. Earlier work on PMJs has been focused on smaller samples of by-eye selected events and case studies. It is our goal to present an automated study of a large sample of PMJs to place the basic statistics of PMJs on a sure footing and to study the PMJ Ca II 8542 Angstrom spectral profile in detail. High spatial resolution and spectrally well-sampled observations in the Ca II 8542 Angstrom line obtained from the Swedish 1-m Solar Telescope (SST) are reduced by a Principle Component Analysis and subsequently used in the automated detection of PMJs using the simple learning algorithm k-Nearest Neighbour. PMJ detections were verified with co-temporal Ca H-line observations. A total of 453 tracked PMJ events were found, or 4253 PMJs detections tallied over all timeframes and a detection rate of 21 events per timestep. From these, an average length, width and lifetime of 640 km, 210 km and 90 s were obtained. The average PMJ Ca II 8542 Angstrom line profile is characterized by enhanced inner wings, often in the form of one or two distinct peaks, and a brighter line core as compared to the quiet Sun average. Average blue and red peak positions were determined at -10.4 km/s and +10.2 km/s offsets from the Ca II 8542 Angstrom line core. We found several clusters of PMJ hotspots within the sunspot penumbra, where PMJ events occur in the same general area repeatedly over time. Our results indicate smaller average PMJs sizes and longer lifetimes compared to previously published values, but with statistics still in the same orders of magnitude. The investigation and analysis of the PMJ line profiles strengthen the proposed heating of PMJs to transition region temperatures.Comment: Figures 1, 2, 3, 4 and 11 exhibited artifacts in some pdf-readers, and have been replotted with new graphical settings to remedy this. Apart from slight changes in sizing and fonts, the figures are the same. The arXiv abstract has had tex-syntax removed for better readabilit

Thermodynamic phases and mesonic fluctuations in a chiral nucleon-meson model

Studies of the QCD phase diagram must properly include nucleonic degrees of freedom and their thermodynamics in the range of baryon chemical potentials characteristic of nuclear matter. A useful framework for incorporating relevant nuclear physics constraints in this context is a chiral nucleon-meson effective Lagrangian. In the present paper, such a chiral nucleon-meson model is extended with systematic inclusion of mesonic fluctuations using the functional renormalization group approach. The resulting description of the nuclear liquid-gas phase transition shows a remarkable agreement with three-loop calculations based on in-medium chiral effective field theory. No signs of a chiral first-order phase transition and its critical endpoint are found in the region of applicability of the model, at least up to twice the density of normal nuclear matter and at temperatures T<100 MeV. Fluctuations close to the critical point of the first-order liquid-gas transition are also examined with a detailed study of the chiral susceptibility.Comment: 10 pages, 11 figures; references added, discussions enlarge

Competitiveness of winter wheat stands against weeds: Effects of cultivar choice, row width and drilling direction

The need for competitive crop stands can be regarded as a basic requirement for weed control, potentially reducing the need for direct control measures. One way the crop may suppress weed growth is by the restriction of light through crop shading. As part of the EU-project ²Strategies of weed control in Organic Farming² (WECOF) trials with winter wheat were carried out to evaluate the potential of wheat shading ability as a weed control measure. Factors included were cultivar, row width and drilling direction. Results of the first experimental year are presented

Non-autonomy of AGAMOUS function in flower development: use of a Cre/loxP method for mosaic analysis in Arabidopsis

Angiosperms use a multi-layered meristem (typically L1, L2 and L3) to produce primordia that then develop into plant organs, A number of experiments show that communication between the cell layers is important for normal development. We examined whether the function of the flower developmental control gene AGAMOUS involves communication across these layers. We developed a mosaic strategy using the Cre/loxP site-specific recombinase system, and identified the sector structure for mosaics that produced mutant flowers. The major conclusions were that (1) AGAMOUS must be active in the L2 for staminoid and carpelloid tissues, (2) that AGAMOUS must be active in the L2 and the L3 for floral meristem determinacy, and (3) that epidermal cell identity can be communicated by the L2 to the L1 layer