N-body U and K matrix program

Computer program was devised to compute free-fall trajectories of satellites, allowing for injection errors and midcourse velocity perturbations. Program consists of trajectory perturbing program and N-body integrating conic program which can also be used as 2-body patch conic program

Editorial overview: Neuroscience of education

Research in the field of ‘neuroscience and education’ aims to provide educationally relevant, and empirical evidence using the increasingly more integrated methods of neuroscience, psychology and education. It is important that studies in the field consider the needs of all disciplines and are open to cross-disciplinary communication. All three disciplines can inform each other in introducing methods, integrating potentially diverse research results and theoretical views, and setting research agendas. The diversity of the field in ideas, approaches, methods and theoretical views is key. Debate-free, uniform opinion rarely leads to scientific progress. The current special issue addresses current advances and controversies in some of the major topics in the field of educational neuroscience, i.e., the neuroscience of processes important for education, from science, technology, education and mathematics (STEM) and reading, domain general processes, cognitive training, motivational, affective and social processes, and neurodevelopment

Diffuse radio emission in the complex merging galaxy cluster Abell 2069

Galaxy clusters with signs for a recent merger show in many cases extended diffuse radio features. This emission originates from relativistic electrons which suffer synchrotron losses due to the intra-cluster magnetic field. The mechanisms of the particle acceleration and the properties of the magnetic field are still poorly understood. We search for diffuse radio emission in galaxy clusters. Here, we study the complex galaxy cluster Abell 2069, for which X-ray observations indicate a recent merger. We investigate the cluster's radio continuum emission by deep Westerbork Synthesis Radio Telescope (WSRT) observations at 346 MHz and a Giant Metrewave Radio Telescope (GMRT) observation at 322 MHz. We find an extended diffuse radio feature roughly coinciding with the main component of the cluster. We classify this emission as a radio halo and estimate its lower limit flux density to 25 +/- 9 mJy. Moreover, we find a second extended diffuse source located at the cluster's companion and estimate its flux density to 15 +/- 2 mJy. We speculate that this is a small halo or a mini-halo. If true, this cluster is the first example of a double-halo in a single galaxy cluster.Comment: 6 pages, 3 figures, accepted for publication in A&

Radio relics in cosmological simulations

Radio relics have been discovered in many galaxy clusters. They are believed to trace shock fronts induced by cluster mergers. Cosmological simulations allow us to study merger shocks in detail since the intra-cluster medium is heated by shock dissipation. Using high resolution cosmological simulations, identifying shock fronts and applying a parametric model for the radio emission allows us to simulate the formation of radio relics. We analyze a simulated shock front in detail. We find a rather broad Mach number distribution. The Mach number affects strongly the number density of relativistic electrons in the downstream area, hence, the radio luminosity varies significantly across the shock surface. The abundance of radio relics can be modeled with the help of the radio power probability distribution which aims at predicting radio relic number counts. Since the actual electron acceleration efficiency is not known, predictions for the number counts need to be normalized by the observed number of radio relics. For the characteristics of upcoming low frequency surveys we find that about thousand relics are awaiting discovery.Comment: 10 pages, 4 figures, Invited talk at the conference "Diffuse Relativistic Plasmas", Bangalore, 1-4 March 2011; in press in special issue of Journal of Astrophysics and Astronom

Signatures from a merging galaxy cluster and its AGN population : LOFAR observations of Abell 1682

Reproduced with permission from Astronomy & Astrophysics. © 2019 ESOWe present LOFAR data from 110-180 MHz of the merging galaxy cluster Abell 1682, alongside archival optical, radio, and X-ray data. Our images of 6 arcsec in resolution at low frequencies reveal new structures associated with numerous radio galaxies in the cluster. At a resolution of 20 arcsec we see diffuse emission throughout the cluster over hundreds of kiloparsecs, indicating particle acceleration mechanisms are in play as a result of the cluster merger event and powerful active galactic nuclei. We show that a significant part of the cluster emission is from an old radio galaxy with very steep spectrum emission (having a spectral index of α < -2.5). Furthermore, we identify a new region of diffuse steep-spectrum emission (α < -1.1) as a candidate for a radio halo which is co-spatial with the centre of the cluster merger. We suggest its origin as a population of old and mildly relativistic electrons left over from radio galaxies throughout the cluster which have been re-accelerated to higher energies by shocks and turbulence induced by the cluster merger event. We also note the discovery of six new giant radio galaxies in the vicinity of Abell 1682.Peer reviewedFinal Accepted Versio

Radio observations of the double-relic galaxy cluster Abell 1240

We present LOFAR 120 − 168 MHz images of the merging galaxy cluster Abell 1240 that hosts double radio relics. In combination with the GMRT 595 − 629 MHz and VLA 2 − 4 GHz data, we characterised the spectral and polarimetric properties of the radio emission. The spectral indices for the relics steepen from their outer edges towards the cluster centre and the electric field vectors are approximately perpendicular to the major axes of the relics. The results are consistent with the picture that these relics trace large-scale shocks propagating outwards during the merger. Assuming diffusive shock acceleration (DSA), we obtain shock Mach numbers of M = 2.4 and 2.3 for the northern and southern shocks, respectively. For M ≲ 3 shocks, a pre-existing population of mildly relativistic electrons is required to explain the brightness of the relics due to the high (> 10 per cent) particle acceleration efficiency required. However, for M ≳ 4 shocks the required efficiency is ≳ 1% and ≳ 0.5%, respectively, which is low enough for shock acceleration directly from the thermal pool. We used the fractional polarization to constrain the viewing angle to ≥ 53 ± 3° and ≥ 39 ± 5° for the northern and southern shocks, respectively. We found no evidence for diffuse emission in the cluster central region. If the halo spans the entire region between the relics (∼1.8 Mpc) our upper limit on the power is P1.4 GHz = (1.4 ± 0.6) × 1023 W Hz−1 which is approximately equal to the anticipated flux from a cluster of this mass. However, if the halo is smaller than this, our constraints on the power imply that the halo is underluminous

Alkalilimnicola ehrlichii sp. nov., a novel, arsenite-oxidizing haloalkaliphilic gammaproteobacterium capable of chemoautotrophic or heterotrophic growth with nitrate or oxygen as the electron acceptor

A facultative chemoautotrophic bacterium, strain MLHE-1T, was isolated from Mono Lake, an alkaline hypersaline soda lake in California, USA. Cells of strain MLHE-1T were Gram-negative, short motile rods that grew with inorganic electron donors (arsenite, hydrogen, sulfide or thiosulfate) coupled with the reduction of nitrate to nitrite. No aerobic growth was attained with arsenite or sulfide, but hydrogen sustained both aerobic and anaerobic growth. No growth occurred when nitrite or nitrous oxide was substituted for nitrate. Heterotrophic growth was observed under aerobic and anaerobic (nitrate) conditions. Cells of strain MLHE-1T could oxidize but not grow on CO, while CH4 neither supported growth nor was it oxidized. When grown chemoautotrophically, strain MLHE-1T assimilated inorganic carbon via the Calvin-Benson-Bassham reductive pentose phosphate pathway, with the activity of ribulose 1,5-bisphosphate carboxylase (RuBisCO) functioning optimally at 0.1 M NaCl and at pH 7.3. Strain MLHE-1T grew over broad ranges of pH (7.3-10.0; optimum, 9.3), salinity (115-190 g l-1; optimum 30 g l-1) and temperature (113-40 °C; optimum, 30 °C). Phylogenetic analysis of 16S rRNA gene sequences placed strain MLHE-1T in the class Gammaproteobacteria (family Ectothiorhodospiraceae) and most closely related to Alkalispirillum mobile (98.5%) and Alkalilimnicola halodurans (98.6%), although none of these three haloalkaliphilic micro-organisms were capable of photoautotrophic growth and only strain MLHE-1T was able to oxidize As(III). On the basis of physiological characteristics and DNA-DNA hybridization data, it is suggested that strain MLHE-1T represents a novel species within the genus Alkalilimnicola for which the name Alkalilimnicola ehrlichii is proposed. The type strain is MLHE-1T (=DSM 17681T =ATCC BAA-1101T). Aspects of the annotated full genome of Alkalilimnicola ehrlichii are discussed in the light of its physiology. © 2007 IUMS

Photoelectron diffraction: from phenomenological demonstration to practical tool

The potential of photoelectron diffraction—exploiting the coherent interference of directly-emitted and elastically scattered components of the photoelectron wavefield emitted from a core level of a surface atom to obtain structural information—was first appreciated in the 1970s. The first demonstrations of the effect were published towards the end of that decade, but the method has now entered the mainstream armoury of surface structure determination. This short review has two objectives: First, to outline the way that the idea emerged and the way this evolved in my own collaboration with Neville Smith and his colleagues at Bell Labs in the early years: Second, to provide some insight into the current state-of-the art in application of (scanned-energy mode) photoelectron diffraction to address two key issue in quantitative surface structure determination, namely, complexity and precision. In this regard a particularly powerful aspect of photoelectron diffraction is its elemental and chemical-state specificity