Vegetation-soil relations in a highly sodic landscape, Yelarbon, southern Queensland

Soil and vegetation data were collected from a sodic-scald near Yelarbon in southern Queensland. The surface of the landscape includes relatively light textured pedestals of the A-horizon with slightly alkaline pH and slopes leading down to scalded basement representing the surface of the strongly alkaline B-horizon. The strongest gradient within the floristic patterns was associated with wetland vegetation in drainage lines, but a secondary and orthogonal gradient was related to soil pH, which was probably a function of lower alkalinity on the more stable and weathered A-horizons. There were few significant differences between soil or vegetation characteristics from plot data comparing parts of the landscape with differing historical grazing regimes. Sites included stock routes heavily grazed between the 1920s and 1970s, and subsequently almost ungrazed; and grazed paddocks that have had moderate use throughout this period. There is clear evidence that the area is naturally active in terms of erosion and deposition during flooding regardless of grazing

Unevenly-sampled signals: a general formalism of the Lomb-Scargle periodogram

The periodogram is a popular tool that tests whether a signal consists only of noise or if it also includes other components. The main issue of this method is to define a critical detection threshold that allows identification of a component other than noise, when a peak in the periodogram exceeds it. In the case of signals sampled on a regular time grid, determination of such a threshold is relatively simple. When the sampling is uneven, however, things are more complicated. The most popular solution in this case is to use the "Lomb-Scargle" periodogram, but this method can be used only when the noise is the realization of a zero-mean, white (i.e. flat-spectrum) random process. In this paper, we present a general formalism based on matrix algebra, which permits analysis of the statistical properties of a periodogram independently of the characteristics of noise (e.g. colored and/or non-stationary), as well as the characteristics of sampling.Comment: 10 pages, 11 figures, Astronomy and Astrophysics, in pres

Deep Radio Imaging of Globular Clusters and the Cluster Pulsar Population

We have obtained deep multifrequency radio observations of seven globular clusters using the Very Large Array and the Australia Telescope Compact Array. Five of these, NGC 6440, NGC 6539, NGC 6544, NGC 6624 and Terzan 5 had previously been detected in a shallower survey for steep spectrum radio sources in globular clusters (Fruchter and Goss 1990). The sixth, the rich globular cluster, Liller 1, had heretofore been undetected in the radio, and the seventh, 47 Tucanae, was not included in our original survey. High resolution 6 and 20 cm images of three of the clusters, NGC 6440, NGC 6539, NGC 6624 reveal only point sources coincident with pulsars which have been discovered subsequent to our first imaging survey. 21 and 18 cm images reveal several point sources within a few core-radii of the center of 47 Tuc. Two of these are identified pulsars, and a third, which is both variable and has a steep spectrum, is also most likely a pulsar previously identified by a pulsed survey. However, the 6, 20 and 90 cm images of NGC 6544, Liller 1 and Terzan 5 display strong steep-spectrum emission which cannot be associated with known pulsars. The image of the rich cluster Terzan 5 displays numerous point sources within $30''$, or 4 core radii of the cluster center. The density of these objects rises rapidly toward the core, where an elongated region of emission is found. The brightest individual sources, as well as the extended emission, possess the steep spectra expected of pulsars. Furthermore, the flux distribution of the sources agrees well with the standard pulsar luminosity function. The total luminosity and number of objects observed suggest that Terzan 5 contains more pulsars than any other Galactic globular cluster.Comment: 33 pages, 6 Postscript figures; Accepted for publication in the Astrophysical Journal; abstract abridged. PDF version also available at http://nemesis.stsci.edu/~fruchter/fg99/fg99.pd

Some Exact Results on the Potts Model Partition Function in a Magnetic Field

We consider the Potts model in a magnetic field on an arbitrary graph $G$. Using a formula of F. Y. Wu for the partition function $Z$ of this model as a sum over spanning subgraphs of $G$, we prove some properties of $Z$ concerning factorization, monotonicity, and zeros. A generalization of the Tutte polynomial is presented that corresponds to this partition function. In this context we formulate and discuss two weighted graph-coloring problems. We also give a general structural result for $Z$ for cyclic strip graphs.Comment: 5 pages, late

A catalogue of micro-Jy radio sources in northern legacy fields

We present catalogues of faint 1.4-GHz radio sources from extremely-deep Very Large Array pointings in the Lockman Hole, the Hubble Deep Field North (HDF-N) and ELAIS N2. Our analysis of the HDF-N data has produced maps that are significantly deeper than those previously published and we have used these to search for counterparts to submm sources. For each of the fields we have derived normalised differential source counts and in the case of the HDF-N find no evidence for the previously-reported under-density of sources; our counts are entirely consistent with those found for the majority of other fields. The catalogues are available as an online supplement to this paper and the maps are also available for download.Comment: 10 pages, 6 figures. Accepted for publication in MNRAS. Full resolution versions of Fig. 3 are available from ftp://ftp.roe.ac.uk/pub/adb/vla_deep_fields/ . Catalogues and maps can be obtained from the same ur

Pulsar Radio Emission Altitude from Curvature Radiation

We assume that the relativistic sources moving along the dipolar magnetic field lines emit curvature radiation. The beamed emission occurs in the direction of tangents to the field lines, and to receive it, the sight line must align with the tangent within the beaming angle 1/gamma, where gamma is the particle Lorentz factor. By solving the viewing geometry in an inclined and rotating dipole magnetic field, we show that, at any given pulse phase, observer tends to receive radiation only from the specific heights allowed by the geometry. We find outer conal components are emitted at higher altitudes compared to inner components including the core. At any pulse phase, low frequency emission comes from higher altitudes than high frequency emission. We have modeled the emission heights of pulse components of PSR B0329+54, and estimated field line curvature radii and particle Lorentz factors in the emission regions.Comment: 14 pages, 3 figures. Accepted for Astrophysical Journal, 200

Urocortin, a CRF-like peptide, restores key indicators of damage in the substantia nigra in a neuroinflammatory model of Parkinson's disease

We have recently observed that the corticotrophin releasing hormone (CRF) related peptide urocortin (UCN) reverses key features of nigrostriatal damage in the hemiparkinsonian 6-hydroxydopamine lesioned rat. Here we have studied whether similar effects are also evident in the lipopolysaccaride (LPS) neuroinflammatory paradigm of Parkinson's disease (PD). To do this we have measured restoration of normal motor behaviour, retention of nigral dopamine (DA) and also tyrosine hydroxylase (TH) activity. Fourteen days following intranigral injections of LPS and UCN, rats showed only modest circling after DA receptor stimulation with apomorphine, in contrast to those given LPS and vehicle where circling was pronounced. In separate experiments, rats received UCN seven days following LPS, and here apomorphine challenge caused near identical circling intensity to those that received LPS and UCN concomitantly. In a similar and consistent manner with the preservation of motor function, UCN 'protected' the nigra from both DA depletion and loss of TH activity, indicating preservation of DA cells. The effects of UCN were antagonised by the non-selective CRF receptor antagonist α-helical CRF and were not replicated by the selective CRF2 ligand UCN III. This suggests that UCN is acting via CRF1 receptors, which have been shown to be anti-inflammatory in the periphery. Our data therefore indicate that UCN is capable of maintaining adequate nigrostriatal function in vivo, via CRF1 receptors following a neuro-inflammatory challenge. This has potential therapeutic implications in PD

Modeling the Images of Relativistic Jets Lensed by Galaxies with Different Mass Surface Density Distributions

The images of relativistic jets from extragalactic sources produced by gravitational lensing by galaxies with different mass surface density distributions are modeled. In particular, the following models of the gravitational lens mass distribution are considered: a singular isothermal ellipsoid, an isothermal ellipsoid with a core, two- and three-component models with a galactic disk, halo, and bulge. The modeled images are compared both between themselves and with available observations. Different sets of parameters are shown to exist for the gravitationally lensed system B0218+357 in multicomponent models. These sets allow the observed geometry of the system and the intensity ratio of the compact core images to be obtained, but they lead to a significant variety in the Hubble constant determined from the modeling results.Comment: 26 pages, 9 figures, will be published in the Astronomy Letters, 2011, v.37, N4, pp. 233-24