1,220 research outputs found
The high-field polar RX J1007.5-2017
We report optical and X-ray observations of the high-field polar
RXJ1007.5-2017 performed between 1990 and 2012. It has an orbital period of
208.60 min determined from the ellipsoidal modulation of the secondary star in
an extended low state. The spectral flux of the dM3- secondary star yields a
distance of 790+-105 pc. At low accretion levels, \RX{} exhibits pronounced
cyclotron emission lines. The second and third harmonic fall in the optical
regime and yield a field strength in the accretion spot of 94 MG. The source is
highly variable on a year-to-year basis and was encountered at visual
magnitudes between V \sim 20 and V \sim 16. In the intermediate state of 1992
and 2000, the soft X-ray luminosity exceeds the sum of the luminosities of the
cyclotron source, the hard X-ray source, and the accretion stream by an order
of magnitude. An X-ray high state, corresponding to the brightest optical
level, has apparently not been observed so far.Comment: To be published in A&
A survey thesis of the personal reading preferences of children in the intermediate grades
Thesis (Ed.M.)--Boston Universit
Parent-of-origin effects cause genetic variation in pig performance traits
In order to assess the relative importance of genomic imprinting for the genetic variation of traits economically relevant for pork production, a data set containing 21 209 records from Large White pigs was analysed. A total of 33 traits for growth, carcass composition and meat quality were investigated. All traits were recorded between 1997 and 2006 at a test station in Switzerland and the pedigree included 15 747 ancestors. A model with two genetic effects for each animal was applied: the first corresponds to a paternal and the second to a maternal expression pattern of imprinted genes. The imprinting variance was estimated as the sum of both corresponding genetic variances per animal minus twice the covariance. The null hypothesis of no imprinting was tested by a restricted maximum likelihood ratio test with two degrees of freedom. Genomic imprinting significantly contributed to the genetic variance of 19 traits. The proportion of the total additive genetic variance that could be attributed to genomic imprinting was of the order between 5% and 19
Untersuchungen an Köhler und Blauleng in den Fanggebieten westlich und nördlich der Britischen Inseln - (96. Reise des FFS "Walther Herwig" vom 28.02. bis 31.03.1989)
Herkunftsvergleiche von Legehennen in Station und Feld unter besonderer Berücksichtigung ökologischer Haltungsverfahren
Der Beitrag beschreibt die Bedingungen von Legeleistungsprüfungen in Deutschland mit Bezug auf Genotyp Umwelt-Interaktionen. Außerdem werden die Besonderheiten der Eierproduktion auf ökologischer Basis herausgestellt. Daraus werden Anregungen für ein Konzept einer zukünftigen Feldprüfung von Legehennen erarbeitet. In Deutschland werden keine offiziellen Legeleistungsprüfungen der Länder mehr durchgeführt. Unabhängige Leistungsinformationen aus Herkunftsvergleichen stehen daher nur aus einzelnen Prüfungen (LfL Bayern, 2006) zur Verfügung. Interaktionen zwischen Legehennenherkünften und unterschiedlichen Haltungssystemen sind nach Literaturangaben gut belegt. Für die Ökoproduktion von Eiern ist aufgrund der produktionstechnischen Unterschiede zur konventionellen Produktion ebenfalls mit solchen Wechselwirkungen zu rechnen. Deshalb braucht die ökologische Eierproduktion eine Leistungsprüfung, die auf die speziellen Produktionsbedingungen abgestimmt ist. Die Entwicklung eines Feldtests für Legehennen in ökologischer Haltung kann daher ein Weg sein, das gegenwärtige Informationsdefizit der Landwirte über die Leistung und das Verhalten erhältlicher Zuchtprodukte unter Öko-Bedingungen zu verringern. Das Konzept muss eine praktikable Datenerfassung gewährleisten. Ein geeignetes und kostengünstig durchführbares Versuchsdesign zur Ermittlung der durchschnittlichen Eignung von Legehennenherkünften für die ökologische Haltung muss dazu entwickelt werden
Neglected X-ray discovered polars: III. RX J0154.0-5947, RX J0600.5-2709, RX J0859.1+0537, RX J0953.1+1458, and RX J1002.2-1925
We report results on the ROSAT-discovered noneclipsing short-period polars RX
J0154.0-5947, RX J0600.5-2709, RX J0859.1+0537, RX J0953.1+1458, and RX
J1002.2-1925 collected over 30 years. We present accurate linear orbital
ephemerides that allow a correct phasing of data taken decades apart. Three of
the systems show cyclotron and Zeeman lines that yield magnetic field strengths
of 36 MG, 19 MG, and 33 MG for the last three targets, respectively. RX
J0154.0-5947, RX J0859.1+0537, and RX J1002.2-1925 show evidence for part-time
accretion at both magnetic poles, while RX J0953.1+1458 is a polar with a
stable one-pole geometry. RX J1002.2-1925 shows large variations in the shapes
of its light curves that we associate with an unstable accretion geometry.
Nevertheless, it appears to be synchronized. We determined the bolometric soft
and hard X-ray fluxes and the luminosities at the Gaia distances of the five
stars. Combined with estimates of the cyclotron luminosities, we derived
high-state accretion rates that range from
yr to yr for white
dwarf masses between 0.61 and 0.82 , in agreement with predictions
based on the observed effective temperatures of white dwarfs in polars and the
theory of compressional heating. Our analysis lends support to the hypothesis
that different mean accretion rates appply for the subgroups of short-period
polars and nonmagnetic cataclysmic variables.Comment: 24 pages, 11 figures, and 13 tables, accepted for publication in A&
Wakefields in superconducting rf cavities and the impact on vacuum ultraviolet free-electron laser oscillator performance
The Fermilab Accelerator Science and Technology facility is currently in operation with its linac based on TESLA-type superconducting rf cavities. Using a 3-MHz micropulse repetition rate with a long macropulse composed of up to 3000 micropulses, and with beam energies demonstrated at 300 MeV and projected to reach 800 MeV with two additional cryomodules, the feasibilities for a vacuum ultraviolet (VUV) and an extreme ultraviolet (EUV) free-electron laser oscillator (FELO) with the two energies are evaluated. We have used both the ginger code with an oscillator module and the minerva/opc code to assess FELO saturation prospects at 120 nm with a 5.0-cm-period undulator of 4.5-m length and the minerva/opc code to assess the FELO at 13.4 nm with adjusted parameters. The simulation results support saturation at both of these wavelengths which are much shorter than the demonstrated shortest wavelength record of 168.6 nm from a storage-ring-based FELO. This indicates superconducting rf linac-driven FELOs can be extended into this VUV-EUV wavelength regime previously only reached with single-pass FEL configurations. In addition, emittance-dilution effects due to wakefields in the cavities and the resulting submacropulse centroid slew effects on FELO performance are addressed using minerva/opc simulations for the first time.</p
Cylindrical Magnets and Ideal Solenoids
Both wire-wound solenoids and cylindrical magnets can be approximately
modeled as ideal, azimuthally symmetric solenoids. We present here an exact
solution for the magnetic field of an ideal solenoid in an especially easy to
use form. The field is expressed in terms of a single function that can be
rapidly computed by means of a compact, highly efficient algorithm, which can
be coded as an add-in function to a spreadsheet, making field calculations
accessible even to introductory students. In computational work these
expressions are not only accurate but also just as fast as most approximate
expressions. We demonstrate their utility by numerically simulating the
experiment of dropping a cylindrical magnet through a nonmagnetic conducting
tube and then comparing the calculation with data obtained from experiments
suitable for an undergraduate laboratory.Comment: 12 pages, 5 figures, revTe
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