Spectral shifts in quasi-stellar objects

Red and blue shift frequency distribution of quasi-stellar objects from nearby galaxie

A Land Market Cycle in the Netherlands

This paper develops a disequilibrium model of land prices in the Netherlands. It shows that the behaviour of traded quantities and prices of Dutch land have some resemblance with a disequilibrium land market model developed by Søgaard. An error correction model based on Søgaard’s model generates significant results with GDP and the real interest rate as explanatory variables, but regrettably farm income nor government demand for land generate significant results. If the model is correct, bubbles are characteristic for the Dutch land market, and this suggests that there is an opportunity for Dutch government to improve on the timing of buying land for nature policy.land market cycle, land prices, nature policy, Land Economics/Use,

A Model for the Moving `Wisps' in the Crab Nebula

I propose that the moving `wisps' near the center of the Crab Nebula result from nonlinear Kelvin-Helmholtz instabilities in the equatorial plane of the shocked pulsar wind. Recent observations suggest that the wisps trace out circular wavefronts in this plane, expanding radially at speeds approximately less than c/3. Instabilities could develop if there is sufficient velocity shear between a faster-moving equatorial zone and a slower moving shocked pulsar wind at higher latitudes. The development of shear could be related to the existence of a neutral sheet -- with weak magnetic field -- in the equatorial zone, and could also be related to a recent suggestion by Begelman that the magnetic field in the Crab pulsar wind is much stronger than had been thought. I show that plausible conditions could lead to the growth of instabilities at the radii and speeds observed, and that their nonlinear development could lead to the appearance of sharp wisplike features.Comment: 7 pages; 3 postscript figures; LaTex, uses emulateapj.sty; to Appear in the Astrophysical Journal, Feb. 20, 1999, Vol. 51

Perfect magnetohydrodynamics as a field theory

We propose the generally covariant action for the theory of a self-coupled complex scalar field and electromagnetism which by virtue of constraints is equivalent, in the regime of long wavelengths, to perfect magnetohydrodynamics (MHD). We recover from it the Euler equation with Lorentz force, and the thermodynamic relations for a prefect fluid. The equation of state of the latter is related to the scalar field's self potential. We introduce 1+3 notation to elucidate the relation between MHD and field variables. In our approach the requirement that the scalar field be single valued leads to the quantization of a certain circulation in steps of $\hbar$; this feature leads, in the classical limit, to the conservation of that circulation. The circulation is identical to that in Oron's generalization of Kelvin's circulation theorem to perfect MHD; we here characterize the new conserved helicity associated with it. We also demonstrate the existence for MHD of two Bernoulli-like theorems for each spacetime symmetry of the flow and geometry; one of these is pertinent to suitably defined potential flow. We exhibit the conserved quantities explicitly in the case that two symmetries are simultaneously present, and give examples. Also in this case we exhibit a new conserved MHD circulation distinct from Oron's, and provide an example.Comment: RevTeX, 16 pages, no figures; clarifications added and typos corrected; version to be published in Phys. Rev.

The nature of the absorbing torus in compact Radio Galaxies

We present BeppoSAX observations of the two radio galaxies PKS 1934-63 and S5 1946+708. Strong Iron Kalpha lines are detected in both objects indicating that the two sources are absorbed by column densities higher than 10^24 cm^(-2). Combining radio continuum, HI absorption and X-ray data we can constrain the physical state and the dimensions of the absorber. We find that the putative obscuring torus is molecular and located at a distance higher than 20 pc from the center in S5 1946+70. In PKS 1934-63 no radio nucleus has been observed. If this is due to free-free absorption a radius of only a few pc is inferred. Since the Kalpha lines have been detected only at 90% confidence, we also discuss the implications if they would be not as strong as found from our data. From our results it appears that the combination of hard X-ray data and spatially resolved HI absorption measurements provides a powerful diagnostic for conditions in the absorbing ``torus''.Comment: 8 pages, 5 figures, accepted for publication in Astronomy & Astrophysic

Doubly Helical Coronal Ejections from Dynamos and their Role in Sustaining the Solar Cycle

Two questions about the solar magnetic field might be answered together once their connection is identified. The first is important for large scale dynamo theory: what prevents the magnetic backreaction forces from shutting down the dynamo cycle? The second question is: what determines the handedness of twist and writhe in magnetized coronal ejecta? Magnetic helicity conservation is important for answering both questions. Conservation implies that dynamo generation of large scale writhed structures is accompanied by the oppositely signed twist along these structures. The latter is associated with the backreaction force. We suggest that coronal mass ejections (CME's) simultaneously liberate small scale twist and large scale writhe of opposite sign, helping to prevent the cycle from quenching and enabling a net magnetic flux change in each hemisphere. Observations and helicity spectrum measurements from a simulation of a rising flux ribbon support this idea. We show a new pictorial of dynamo flux generation that includes the backreaction and magnetic helicity conservation by characterizing the field as a 2-D ribbon rather than a 1-D line.Comment: 11 pages LaTeX, 2 figures (last 2 pages), submitted to ApJ

The Supernova Remnant CTB104A : Magnetic Field Structure and Interaction with the Environment

We present new, high resolution 1420 and 408 MHz continuum images and HI and 12CO (J=1-0) spectral line maps of the diffuse supernova remnant CTB104A (G93.7-0.3). Analysis of the complex continuum emission reveals no significant spectral index variations across the remnant. Three prominences around CTB104A are found to be related to the SNR, while one extension to the east is identified as an HII region associated with a background molecular shell. Small scale polarization and rotation measure (RM) structures are turbulent in nature, but we find a well-ordered RM gradient across the remnant, extending from southeast to northwest. This gradient does not agree with the direction of the global Galactic magnetic field, but does agree with a large-scale RM anomaly inferred from rotation measure data by Cleg et al. (1992). We show that the observed morphology of CTB104A is consistent with expansion in a uniform magnetic field, and this is supported by the observed RM distribution. By modeling the RM gradient with a simple compression model we have determined the magnetic field strength within the remnant as Bo ~ 2.3 micro G. We have identified signatures of the interaction of CTB104A with the surrounding neutral material, and determined its distance, from the kinematics of the HI structure encompassing the radio emission, as 1.5 kpc. We also observed clear breaks in the HI shell that correspond well to the positions of two of the prominences, indicating regions where hot gas is escaping from the interior of the SNR.Comment: 7 pages, Latex with aastex and emulateapj5, 12 figures, ApJ accepte

The X-ray emission of the most luminous 3CR radio sources

We investigate the X-ray properties of the most luminous radio sources in the 3CR catalogue, in order to assess if they are similar to the most luminous radio quiet quasars, for instance in the X-ray normalization with respect to the optical luminosity, or in the distribution of the absorption column density. We have selected the (optically identified) 3CR radio sources whose 178-MHz monochromatic luminosity lies in the highest factor-of-three bin. The 4 most luminous objects had already been observed in X rays. Of the remaining 16, we observed with XMM-Newton 4 randomly chosen, optical type 1s, and 4 type 2s. All targets have been detected. The optical-to-Xray spectral index, alphaox, can be computed only for the type 1s and, in agreement with previous studies, is found to be flatter than in radio quiet quasars of similar luminosity. However, the Compton thin type 2s have an absorption corrected X-ray luminosity systematically lower than the type 1s, by a factor which makes them consistent with the radio quiet alphaox. Within the limited statistics, the Compton thick objects seem to have a reflected component more luminous than the Compton thin ones. The extra X-ray component observed in type 1 radio loud quasars is beamed for intrinsic causes, and is not collimated by the absorbing torus as is the case for the (intrinsically isotropic) disk emission. The extra component can be associated with a relativistic outflow, provided that the flow opening angle and the Doppler beaming factor are 1/5 - 1/7 radians.Comment: LaTex, 6 pages, 3 figures, 3 tables; accepted for publication in A&

A case of recurrent epilepsy-associated rosette-forming glioneuronal tumor with anaplastic transformation in the absence of therapy.

Rosette-forming glioneuronal tumor (RGNT) most commonly occurs adjacent to the fourth ventricle and therefore rarely presents with epilepsy. Recent reports describe RGNT occurrence in other anatomical locations with considerable morphologic and genetic overlap with the epilepsy-associated dysembryoplastic neuroepithelial tumor (DNET). Examples of RGNT or DNET with anaplastic change are rare, and typically occur in the setting of radiation treatment. We present the case of a 5-year-old girl with seizures, who underwent near total resection of a cystic temporal lobe lesion. Pathology showed morphologic and immunohistochemical features of RGNT, albeit with focally overlapping DNET-like patterns. Resections of residual or recurrent tumor were performed 1 year and 5 years after the initial resection, but no adjuvant radiation or chemotherapy was given. Ten years after the initial resection, surveillance imaging identified new and enhancing nodules, leading to another gross total resection. This specimen showed areas similar to the original tumor, but also high-grade foci with oligodendroglial morphology, increased cellularity, palisading necrosis, microvascular proliferation, and up to 13 mitotic figures per 10 high power fields. Ancillary studies the status by sequencing showed wild-type of the isocitrate dehydrogenase 1 (IDH1), IDH2, and human histone 3.3 (H3F3A) genes, and BRAF studies were negative for mutation or rearrangement. Fluorescence in situ hybridization (FISH) showed codeletion of 1p and 19q limited to the high-grade regions. By immunohistochemistry there was loss of nuclear alpha-thalassemia mental retardation syndrome, X-linked (ATRX) expression only in the high-grade region. Next-generation sequencing showed an fibroblast growth factor receptor receptor 1 (FGFR1) kinase domain internal tandem duplication in three resection specimens. ATRX mutation in the high-grade tumor was confirmed by sequencing which showed a frameshift mutation (p.R1427fs), while the apparent 1p/19q-codeletion by FISH was due to loss of chromosome arm 1p and only partial loss of 19q. Exceptional features of this case include the temporal lobe location, 1p/19q loss by FISH without true whole-arm codeletion, and anaplastic transformation associated with ATRX mutation without radiation or chemotherapy