Signatures of restarted activity in core-dominated, triple radio sources selected from the FIRST survey

Signatures of the re-occurrence of activity in radio-loud AGNs, indicated either by the so-called double-double or X-shaped structures, have been observed in a number of radio sources. All such objects known to date have linear sizes of the order of a megaparsec. A number of the sources that are appreciably more compact than this, but that exhibit hints of a past phase of activity, were found in the VLA FIRST survey. Their structures show symmetric relic lobes straddling relatively bright, unresolved cores. Observations of the cores of 15 such structures with MERLIN at 5 GHz have shown that four of them are doubles or core-jets on the subarcsecond scale. Misalignments of \Delta PA \ga 30 degr. between the axis of the inner structure and the line connecting the fitted maxima of the arcminute-scale relic lobes are clearly visible in three of the four sources. From these results, we can infer that a rapid repositioning of the central engine in each of these three radio sources is the most plausible interpretation of the observed morphology and that a merger is most likely the original cause of such a repositioning. In the case of TXS 1033+026, the optical image extracted from the SDSS archives clearly suggests that two objects separated by only 2.7 kpc (projected onto the sky plane) are indeed merging. The inner parts of TXS 0818+214 and TXS 1312+563 could be interpreted as double-lobed, and consequently, these sources could be of the double-double type; but further multifrequency observations are necessary to provide support for such an interpretation.Comment: 9 pages, 5 figures, matches the version printed in Astronomy & Astrophysics, very minor correction of Table

Broadband nuclear emission in two radio-loud BAL quasars

The X-ray weakness of broad absorption line (BAL) quasars in comparison to non-BAL objects is possibly caused by the absorption of X-ray emission by the shielding material near the equatorial plane. On the other hand, the radio-loud BALQSOs are more X-ray loud than the radio-quiet ones. This suggests that part of the X-ray emission may arise from the radio jet. To investigate this possibility, we modelled the nuclear spectra of two radio-loud BALQSOs. We focus on the emission from the very centres of these two objects. The source of emission was approximated by a single, homogeneous component that produces synchrotron and inverse-Compton (IC) radiation. The simplicity of the model allowed us to estimate the basic physical parameters of the emitting regions, using a universal analytic approach. Such methods have already been used in blazars. For the first time we propose this solution for quasars. In addition, we modelled the radiation spectra of the accretion disk and its corona to compare them with the jets' spectra. We find that in the case of luminous 3C270.1, the nuclear X-ray continuum is dominated by the non-thermal, IC emission from the innermost parts of the radio jet. However, the radio core of the lobe-dominated PG 1004+130 is probably too weak to produce significant part of the observed X-ray emission. A large contribution from the X-ray emitting accretion disk and corona is produced in our model. However, it then exceeds the observed flux. Because the large intrinsic absorption was postulated recently by the NuSTAR observations, we propose that the disk-corona component may still account for the X-rays produced in this source. This part of the spectrum must nevertheless be dominated by the X-ray jet. We conclude that the jet-linked X-ray emission is present in strong and weak radio sources, but its fraction seems to scale with the radio jet power.Comment: 10 pages, 6 figures. Accepted to Astronomy and Astrophysics. Online material (Appendix) will be available at A&

Developing DNA barcoding (matK) primers for marama bean [Tylosema esculentum (Burchell) Schreiber]

DNA barcoding is based on the premise that a short standardized DNA barcoding sequence can distinguish individuals of a species because the genetic variation between species exceeds that within species. Information on genetic variation of breeding materials helps to maintain genetic diversity and sustains long term selection gain. This information is a prerequisite for the genetic improvement of any plant species for effective use of germplasm in breeding and for conservation. Marama bean [Tylosema esculentum (Burchell) Schreiber] is found in the arid, dry parts of Southern Africa and due to the high nutrient value of the seeds and tubers, richness in protein, oil and starch, it is a potential crop for arid areas where few conventional crops can survive. The effective conservation and use of marama bean genetic resources for domestication involves investigating the extent of genetic variation. The matK gene, formerly known as orfK, is emerging as a DNA barcoding gene with potential contribution to plant molecular systematics and evolution. The gene matK, approximately 1500 base pairs (bp), is believed to code for a maturase-related protein based on structural similarities to other such genes. This gene was investigated for potential contribution in genetic variation studies of marama bean and also establishing a barcode for T. esculentum. The matK gene was amplified in marama bean and we reported herein, the first record of sequences of this gene for the species that were found to be related to other legume matK sequences deposited in GenBank. The homology found with Tylosema fassoglensis (trnK gene) and Pisum sativum (matK gene) suggests that an identical region was amplified for Tylosema esculentum. A phylogenetic tree was constructed based on the matK sequences and the results suggest that the matK region can also be used in determining levels of genetic variation and for barcoding.Key words: Marama bean, DNA barcoding, genetic variation, maturase kinase

A review of geographical distribution of marama bean [Tylosema esculentum (Burchell) Schreiber] and genetic diversity in the Namibian germplasm

Marama bean [Tylosema esculentum (Burchell) Schreiber] occurs naturally in the drier areas of Southern Africa, including Botswana and Namibia. The implementation of molecular breeding is important to advance the process of securing the world’s food supply. The development of molecular markers is vital for mapping important traits that can then be followed in subsequent breeding programs. This study assessed the distribution of marama bean in Namibia and isolated microsatellite regions for microsatellite primer design for the purpose of determining genetic diversity and construction of molecular genetic maps for marama. This will greatly enhance the process ofdomesticating marama bean, currently a wild plant that is still picked wild and unsustainably. The geographical distribution was geo-referenced using Geographic Positioning System (GPS) points andmicrosatellites were isolated from the germplasm using a modified FIASCO technique. The study revealed widespread, but patchy distribution of marama bean in Namibia. Five Marama beanmicrosatellite enriched libraries were created. The initial results provided vital information for the ongoing marama bean conservation function and improvement program

Current carrier lifetime in doping superlattice crystals

It is shown, that the lifetime of nonequilibrium current carriers in the luminescence process in doping superlattice structures changes in a wide range with increasing the excitation level of the crystal. Two effects are important, i. e., (a) lowdimensional character of the carrier distribution and (b) change in the overlap of electron and hole wave functions. At low excitation, non-radiative recombination can play principal cause in the stabilization of the effective lifetime of current carriers. At high excitation, the effective lifetime of current carriers approaches the value in the bulk crystal. The major attention was given to the compensated GaAs doping superlattices with i-layers (n-i-p-i crystals) and to the structures with no i-layers (n-p-n-p structures). The layer thickness of n-, p-, and i-type were 20, 40, or 60 nm and the concentrations of the dopants Te and Zn made up to 1018 cm3. Photoluminescence spectra and the decay time of the spontaneous emission intensity in the superlattices were measured at the temperature interval from 1 1 to 300 K. The influence of u-particle irradiation and thermal annealing on the luminescence spectra and the carrier lifetime was also investigate