The pulsar spectral index distribution

The flux density spectra of radio pulsars are known to be steep and, to first order, described by a power-law relationship of the form S_{\nu} \propto \nu^{\alpha}, where S_{\nu} is the flux density at some frequency \nu and \alpha is the spectral index. Although measurements of \alpha have been made over the years for several hundred pulsars, a study of the intrinsic distribution of pulsar spectra has not been carried out. From the result of pulsar surveys carried out at three different radio frequencies, we use population synthesis techniques and a likelihood analysis to deduce what underlying spectral index distribution is required to replicate the results of these surveys. We find that in general the results of the surveys can be modelled by a Gaussian distribution of spectral indices with a mean of -1.4 and unit standard deviation. We also consider the impact of the so-called "Gigahertz-peaked spectrum" pulsars. The fraction of peaked spectrum sources in the population with significant turn-over at low frequencies appears to be at most 10%. We demonstrate that high-frequency (>2 GHz) surveys preferentially select flatter-spectrum pulsars and the converse is true for lower-frequency (<1 GHz) surveys. This implies that any correlations between \alpha and other pulsar parameters (for example age or magnetic field) need to carefully account for selection biases in pulsar surveys. We also expect that many known pulsars which have been detected at high frequencies will have shallow, or positive, spectral indices. The majority of pulsars do not have recorded flux density measurements over a wide frequency range, making it impossible to constrain their spectral shapes. We also suggest that such measurements would allow an improved description of any populations of pulsars with 'non-standard' spectra.Comment: 8 pages, 5 figures. Accepted by MNRA

A Southern Hemisphere radar meteor orbit survey

A meteor radar system has been operated on a routine basis near Christchurch, New Zealand, to determine the orbits of Earth-impacting interplanetary dust and meteoroids. The system sensitivity is +13 visual magnitude, corresponding to approximately 100 micron sized meteoroids. With an orbital precision of 2 degrees in angular elements and 10 percent in orbital energy (1/a), the operation yields an average of 1500 orbits daily with a total to date in excess of 10(exp 5). The use of pc's and automated data reduction permit the large orbital data sets we collect to be routinely reduced. Some illustrative examples are presented of the signal formats/processing and the results of data reduction, giving the individual orbital elements and hence the overall distributions. Current studies include the distribution of dust in the inner solar system; the influx of meteoroids associated with near-Earth asteroids; and the orbital structure existing in comet-produced streams

ANALYSIS OF FARM FINANCING AND RISK MANAGEMENT FOR U.S. FARMERS

Significant changes under the 1996 FAIR Act and trade agreements are occurring in the U.S. farm sector. The changes will affect both the source and the magnitude of the business and financial risks that farmers will be required to manage. The objectives of this study were to investigate farmer plans regarding business expansion, timing of expansion, and expected financing of that business expansion and to analyze their financial services and risk management strategies. The study was based on data from a nationwide survey of subscribers to Top Operator farm magazine. The data were categorized into six groups for analysis: demographics, intergenerational transfer, debt characteristics, lender relationships, business expansion, and farmer expectations of their lenders. Statistical techniques were used to evaluate differences among farmers across regions of the country, types of farm businesses, and sizes of farm businesses.Farm credit, expansion plans, debt-to-asset ratio, farm demographics, financial tools, credit sources, financial services, non-traditional lending, Agricultural Finance, Risk and Uncertainty,

The Populations of Comet-Like Bodies in the Solar system

A new classification scheme is introduced for comet-like bodies in the Solar system. It covers the traditional comets as well as the Centaurs and Edgeworth-Kuiper belt objects. At low inclinations, close encounters with planets often result in near-constant perihelion or aphelion distances, or in perihelion-aphelion interchanges, so the minor bodies can be labelled according to the planets predominantly controlling them at perihelion and aphelion. For example, a JN object has a perihelion under the control of Jupiter and aphelion under the control of Neptune, and so on. This provides 20 dynamically distinct categories of outer Solar system objects in the Jovian and trans-Jovian regions. The Tisserand parameter with respect to the planet controlling perihelion is also often roughly constant under orbital evolution. So, each category can be further sub-divided according to the Tisserand parameter. The dynamical evolution of comets, however, is dominated not by the planets nearest at perihelion or aphelion, but by the more massive Jupiter. The comets are separated into four categories -- Encke-type, short-period, intermediate and long-period -- according to aphelion distance. The Tisserand parameter categories now roughly correspond to the well-known Jupiter-family comets, transition-types and Halley-types. In this way, the nomenclature for the Centaurs and Edgeworth-Kuiper belt objects is based on, and consistent with, that for comets.Comment: MNRAS, in press, 11 pages, 6 figures (1 available as postscript, 5 as gif). Higher resolution figures available at http://www-thphys.physics.ox.ac.uk/users/WynEvans/preprints.pd

A high resolution millimetre and submillimetre study of W3

The continuum bolometer receiver on the James Clerk Maxwell telescope has been used to map the dense core of the star formation region W3 with a spatial resolution of 15-20 arcsec. At 350 and 800 μm, the region appears as two principal peaks around the known IR sources IRS4 and IRS5, while at 1100 μm, a further peak is noted which is interpreted as being due to free-free emission around IRS2. Taking into account the free-free contribution to the intensity, the continuum dust emission from the region is found to be consistent with optically thin emission at all of the three wavelengths considered. Values for the dust optical depth, hydrogen column density, mass, and central density have been obtained for each of the main peaks

IMPACTS OF THE FEDERAL AGRICULTURAL IMPROVEMENT AND REFORM ACT OF 1996 (FAIR ACT) ON THE NORTH DAKOTA AGRICULTURAL ECONOMY

The Federal Agriculture Improvement and Reform Act of 1996 (FAIR Act) decouples government farm subsidy payments from both price and production and provides farmers with nearly complete planting flexibility. Government spending under this act will be limited to $35.63 billion for 1996-2002 period. The net farm income for all six representative farms under the 1996 FAIR Act is projected to be higher than under the 1990 farm act early in the forecast period and lower after 1999 under the 1996 FAIR Act. Cropland prices are projected to fall 19.8% between 1996 and 2002 under the 1996 FAIR Act, while cropland prices are projected to fall 18.5% under the 1990 farm act. Cash rental rates are projected to follow cropland prices. Debt-to-asset ratios for most farms, although rising across the forecast period, do not reach levels that imperil credit- worthiness, but in the case of the low profit farm and small size farm the debt-to-asset ratios rise to a level that may imperil credit-worthiness on new borrowing. Note: Figures are not included in the machine readable file--contact the authors for copies.FAIR Act, net farm income, debt-to-asset ratio, cropland prices, land rental rates, farm operating expenses, capitalization rate, Agricultural and Food Policy,