638 research outputs found
Southern Hemisphere automated supernova search
The Perth Astronomy Research Group has developed an automated supernova search program, using the 61 cm Perth–Lowell reflecting telescope at Perth Observatory in Western Australia, equipped with a CCD camera. The system is currently capable of observing about 15 objects per hour, using 3 min exposures, and has a detection threshold of 18th–19th magnitude. The entire system has been constructed using low‐cost IBM‐compatible computers. Two original discoveries (SN 1993K, SN 1994R) have so far been made during automated search runs. This paper describes the hardware and software used for the supernova search program, and shows some preliminary results from the search system
Einfluß unterschiedlicher Anbauarten – mineralisch, organisch, biologisch-dynamisch – auf Kartoffeln: Inhaltsstoffe, Sensorik, Festigkeitskennwerte und bildschaffende Methoden
Grundsätzlich sprachen die Kartoffeln der Sorte ´Granola´ sehr schwach auf die eingesetzten Versuchsfaktoren an, sodaß die Unterschiede selten statistisch abgesichert werden konnten.
Bei denjenigen Inhaltsstoffen, die deutlicher auf den Anbaufaktor Düngermenge ansprachen, reagierten die Knollen der mineralisch gedüngten Varianten eindeutig stärker (Abnahme der Trockenmasse, der Saccharose-, Stärke- und Clorid-Gehalte, Zunahme der Glukose-, Fruktose-, Fluorid- und Asche-Gehalte) als die Vergleichsvarianten. Ein Grund hierfür könnte die schnellere Verfügbarkeit des mineralischen Düngers gewesen sein.
Die biologisch-dynamisch gedüngten Knollen zeigten nur bei drei Parametern dieselbe Reaktion auf die Intensivierung der Düngung wie die organisch gedüngten auf (Zunahme der Chlorid- und Asche-Gehalte, gleichbleibende Fluorid-Gehalte). Bei vier Merkmalen reagierten die biologisch-dynamischen Knollen überhaupt nicht oder sehr gering, wogegen die organisch gedüngten Kartoffeln eine Abnahme im Trockenmasse- und Saccharosegehalt bzw. keine gerichteten Tendenzen in den Glukose- und Fruktosegehalten aufwiesen.
Die Festigkeitskennwerte der mineralisch gedüngten Kartoffeln wurde, im Vergleich zu den beiden anderen Varianten, schwächer bewertet. Die sensorischen Untersuchungen ergaben keine Bevorzugung einzelner Varianten, jedoch, besonders bei der minera-lischen Variante, eine tendenzielle Abnahme der sensorischen Qualität mit zunehmender Düngung. Die Ergebnisse der Untersuchungen zur „Vitalqualität“ mit Hilfe bildschaf-fender Methoden bestätigte die prinzipielle Eignung dieser Methode für ergänzende Qualitätsuntersuchungen.
Eine abschließende Beurteilung der Qualität der unterschiedlichen Anbauvarianten wird erst in Verbindung der bisherigen Daten mit noch zur Analyse anstehenden Parametern (Nitrat, Aminosäuren, Ascorbinsäure, Kalium) möglich sein. Des weiteren wird in laufenden Sortenversuchen geprüft, ob andere Sorten stärker auf die verschiedenen Versuchsfaktoren reagieren
Quality Comparison of Mineral, Organic and Biodynamic Cultivation of Potatoes: Contents, Strength Criteria, Sensory Investigations and Picture-Creating Methods
Nutritional quality of food can be characterized by the content of beneficial and harmful substances. For today’s consumers the most important criteria for buying potatoes are taste, quality and shelf-life.
Biodynamic preparations are used by about 20% of all organic farms in Germany. These preparations do not primarily serve to increase the yield but are said to support the production of high quality food, having balanced nutrient contents and improved shelf-life characteristics.
Since 1993 investigations have been carried out to evaluate the effect of mineral fertilization and organic manuring at varied intensities, combined with application of biodynamic preparations, on some of these parameters.
The potatoes of the variety ´Granola´ responded rather slightly to the factors of the trial, hence statistical differences could be confirmed only in few cases. Tubers deriving from the mineral fertilized plots showed the strongest response to elevated fertilization (decrease in dry matter, sucrose, chloride content and density, and an increase in glucose, fructose, fluoride and ash content). Only in three parameters tubers from the biodynamic plots responded in the same way as the organic ones to elevated fertilization (increase in the chloride and ash contents, stagnating fluoride contents). In four parameters, no or only a weak response of the biodynamic tubers has been found, whereas organic potatoes showed decreasing dry matter and sucrose contents, but no distinctive tendency in the parameters glucose and fructose. The parameter strength criteria has been assessed as the weakest in mineral fertilized potatoes. The sensory investigations did not allow to differentiate between the three cropping systems but there was a tendency of worsening sensoric quality at increased fertilization, particularly in the tubers of the mineral plots. The results of the determination of vital quality following picture-creating methods confirmed the applicability of this assay for additional quality determinations.
A final assessment of the quality according to the different cropping systems cannot be made at this point of time. Therefore, further parameters (nitrate, potassium, amino acids, ascorbic acid) will be analyzed which might allow a final assessment in combination with the present data. Furthermore, current trials might reveal if other varieties respond stronger to the relevant factors
Multidimensional continued fractions, dynamical renormalization and KAM theory
The disadvantage of `traditional' multidimensional continued fraction
algorithms is that it is not known whether they provide simultaneous rational
approximations for generic vectors. Following ideas of Dani, Lagarias and
Kleinbock-Margulis we describe a simple algorithm based on the dynamics of
flows on the homogeneous space SL(2,Z)\SL(2,R) (the space of lattices of
covolume one) that indeed yields best possible approximations to any irrational
vector. The algorithm is ideally suited for a number of dynamical applications
that involve small divisor problems. We explicitely construct renormalization
schemes for (a) the linearization of vector fields on tori of arbitrary
dimension and (b) the construction of invariant tori for Hamiltonian systems.Comment: 51 page
The distribution of transit durations for Kepler planet candidates and implications for their orbital eccentricities
‘In these times, during the rise in the popularity of institutional repositories, the Society does not forbid authors from depositing their work in such repositories. However, the AAS regards the deposit of scholarly work in such repositories to be a decision of the individual scholar, as long as the individual's actions respect the diligence of the journals and their reviewers.’ Original article can be found at : http://iopscience.iop.org/ Copyright American Astronomical SocietyDoppler planet searches have discovered that giant planets follow orbits with a wide range of orbital eccentricities, revolutionizing theories of planet formation. The discovery of hundreds of exoplanet candidates by NASA's Kepler mission enables astronomers to characterize the eccentricity distribution of small exoplanets. Measuring the eccentricity of individual planets is only practical in favorable cases that are amenable to complementary techniques (e.g., radial velocities, transit timing variations, occultation photometry). Yet even in the absence of individual eccentricities, it is possible to study the distribution of eccentricities based on the distribution of transit durations (relative to the maximum transit duration for a circular orbit). We analyze the transit duration distribution of Kepler planet candidates. We find that for host stars with T > 5100 K we cannot invert this to infer the eccentricity distribution at this time due to uncertainties and possible systematics in the host star densities. With this limitation in mind, we compare the observed transit duration distribution with models to rule out extreme distributions. If we assume a Rayleigh eccentricity distribution for Kepler planet candidates, then we find best fits with a mean eccentricity of 0.1-0.25 for host stars with T ≤ 5100 K. We compare the transit duration distribution for different subsets of Kepler planet candidates and discuss tentative trends with planetary radius and multiplicity. High-precision spectroscopic follow-up observations for a large sample of host stars will be required to confirm which trends are real and which are the results of systematic errors in stellar radii. Finally, we identify planet candidates that must be eccentric or have a significantly underestimated stellar radius.Peer reviewedFinal Accepted Versio
Theory of Stellar Oscillations
In recent years, astronomers have witnessed major progresses in the field of
stellar physics. This was made possible thanks to the combination of a solid
theoretical understanding of the phenomena of stellar pulsations and the
availability of a tremendous amount of exquisite space-based asteroseismic
data. In this context, this chapter reviews the basic theory of stellar
pulsations, considering small, adiabatic perturbations to a static, spherically
symmetric equilibrium. It starts with a brief discussion of the solar
oscillation spectrum, followed by the setting of the theoretical problem,
including the presentation of the equations of hydrodynamics, their
perturbation, and a discussion of the functional form of the solutions.
Emphasis is put on the physical properties of the different types of modes, in
particular acoustic (p-) and gravity (g-) modes and their propagation cavities.
The surface (f-) mode solutions are also discussed. While not attempting to be
comprehensive, it is hoped that the summary presented in this chapter addresses
the most important theoretical aspects that are required for a solid start in
stellar pulsations research.Comment: Lecture presented at the IVth Azores International Advanced School in
Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars
and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta,
Azores Islands, Portugal in July 201
Integer quantum Hall effect for hard-core bosons and a failure of bosonic Chern-Simons mean-field theories for electrons at half-filled Landau level
Field-theoretical methods have been shown to be useful in constructing simple
effective theories for two-dimensional (2D) systems. These effective theories
are usually studied by perturbing around a mean-field approximation, so the
question whether such an approximation is meaningful arises immediately. We
here study 2D interacting electrons in a half-filled Landau level mapped onto
interacting hard-core bosons in a magnetic field. We argue that an interacting
hard-core boson system in a uniform external field such that there is one flux
quantum per particle (unit filling) exhibits an integer quantum Hall effect. As
a consequence, the mean-field approximation for mapping electrons at
half-filling to a boson system at integer filling fails.Comment: 13 pages latex with revtex. To be published in Phys. Rev.
Short-Range Interactions and Scaling Near Integer Quantum Hall Transitions
We study the influence of short-range electron-electron interactions on
scaling behavior near the integer quantum Hall plateau transitions. Short-range
interactions are known to be irrelevant at the renormalization group fixed
point which represents the transition in the non-interacting system. We find,
nevertheless, that transport properties change discontinuously when
interactions are introduced. Most importantly, in the thermodynamic limit the
conductivity at finite temperature is zero without interactions, but non-zero
in the presence of arbitrarily weak interactions. In addition, scaling as a
function of frequency, , and temperature, , is determined by the
scaling variable (where is the exponent for the temperature
dependence of the inelastic scattering rate) and not by , as it would
be at a conventional quantum phase transition described by an interacting fixed
point. We express the inelastic exponent, , and the thermal exponent, ,
in terms of the scaling dimension, , of the interaction strength
and the dynamical exponent (which has the value ), obtaining
and .Comment: 9 pages, 4 figures, submitted to Physical Review
Macroscopic Quantum Fluctuations in the Josephson Dynamics of Two Weakly Linked Bose-Einstein Condensates
We study the quantum corrections to the Gross-Pitaevskii equation for two
weakly linked Bose-Einstein condensates. The goals are: 1) to investigate
dynamical regimes at the borderline between the classical and quantum behaviour
of the bosonic field; 2) to search for new macroscopic quantum coherence
phenomena not observable with other superfluid/superconducting systems. Quantum
fluctuations renormalize the classical Josephson oscillation frequencies. Large
amplitude phase oscillations are modulated, exhibiting collapses and revivals.
We describe a new inter-well oscillation mode, with a vanishing (ensemble
averaged) mean value of the observables, but with oscillating mean square
fluctuations. Increasing the number of condensate atoms, we recover the
classical Gross-Pitaevskii (Josephson) dynamics, without invoking the
symmetry-breaking of the Gauge invariance.Comment: Submitte
Universality of Frequency and Field Scaling of the Conductivity Measured by Ac-Susceptibility of a Ybco-Film
Utilizing a novel and exact inversion scheme, we determine the complex linear
conductivity from the linear magnetic ac-susceptibility
which has been measured from 3\,mHz to 50\,MHz in fields between 0.4\,T and
4\,T applied parallel to the c-axis of a 250\,nm thin disk. The frequency
derivative of the phase and the dynamical scaling of
above and below provide clear evidence for a
continuous phase transition at to a generic superconducting state. Based
on the vortex-glass scaling model, the resulting critical exponents and
are close to those frequently obtained on films by other means and
associated with an 'isotropic' vortex glass. The field effect on
can be related to the increase of the glass coherence length,
.Comment: 8 pages (5 figures upon request), revtex 3.0, APK.94.01.0
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