601 research outputs found
Bedeutung der funktionellen Einheit fĂŒr die Ăkobilanzierung in der Landwirtschaft
Life cycle assessment (LCA) gains increasingly in technical and legal importance. Research groups getting involved with this topic have to adhere to the technical standard. The definition of appropriate reference values, indicated as functional units, is of special importance in this concern. LCA is often derived from the industrial sector, where it is one-dimensionally treated via output of companies. In the agricultural sector at least the problem of land use management has additionally to be considered. This paper shows the development of a convenient solution for this purpose in agricultural consultancy
On the interpretation of the long-term cyclic period variations in RR Lyrae stars
Many RR Lyrae stars show long-term variations of their pulsation period, some
of them in a cyclic way. Such behaviour can be attributed to the light-travel
time effect (LTTE) caused by an unseen companion. Solutions of the LTTE often
suggest very eccentric orbits and minimal mass of the companion on the order of
several solar masses, thus, in the black hole range. We discuss the possibility
of the occurrence of the RR Lyr-black hole pairs and on the case of Z CVn
demonstrate that the LTTE hypothesis can be false in some of the binary
candidates.Comment: 5 pages, 2 figures, published in the proceedings of "The RR Lyrae
2017 Conference", Niepolomice, Poland, 17-21 September 201
A cautionary tale of interpreting O-C diagrams: period instability in a classical RR Lyr Star Z CVn mimicking as a distant companion
We present a comprehensive study of Z CVn, an RR Lyrae star that shows
long-term cyclic variations of its pulsation period. A possible explanation
suggested from the shape of the O-C diagram is the light travel-time effect,
which we thoroughly examine. We used original photometric and spectroscopic
measurements and investigated the period evolution using available maximum
times spanning more than one century. If the binary hypothesis is valid, Z CVn
orbits around a black hole with minimal mass of
on a very wide ( years) and eccentric orbit (). We
discuss the probability of a formation of a black hole-RR Lyrae pair and,
although we found it possible, there is no observational evidence of the black
hole in the direction to Z CVn. However, the main objection against the binary
hypothesis is the comparison of the systemic radial velocity curve model and
spectroscopic observations that clearly show that Z CVn cannot be bound in such
a binary. Therefore, the variations of pulsation period are likely intrinsic to
the star. This finding represents a discovery/confirmation of a new type of
cyclic period changes in RR Lyrae stars. By the analysis of our photometric
data, we found that the Blazhko modulation with period of 22.931 d is strongly
dominant in amplitude. The strength of the phase modulation varies and is
currently almost undetectable. We also estimated photometric physical
parameters of Z CVn and investigated their variations during the Blazhko cycle
using the Inverse Baade-Wesselink method.Comment: 15 pages, 8 tables, 9 figures, accepted for publication in MNRA
Class I Gap-formation in Highly-viscous Glass-ionomer Restorations: Delayed vs Immediate Polishing
This in vitro study evaluated the effects of delayed versus immediate polishing to permit maturation of interfacial gap-formation around highly viscous conventional glass-ionomer cement (HV-GIC) in Class I restorations, together with determining the associated mechanical properties. Cavity preparations were made on the occlusal surfaces of premolars. Three HV-GICs (Fuji IX GP, GlasIonomer FX-II and Ketac Molar) and one conventional glass-ionomer cement (C-GIC, Fuji II, as a control) were studied, with specimen subgroups (n=10) for each property measured. After polishing, either immediately (six minutes) after setting or after 24 hours storage, the restored teeth were sectioned in a mesiodistal direction through the center of the model Class I restorations. The presence or absence of interfacial-gaps was measured at 1000Ă magnification at 14 points (each 0.5-mm apart) along the cavity restoration interface (n=10; total points measured per group = 140). Marginal gaps were similarly measured in Teflon molds as swelling data, together with shear-bond-strength to enamel and dentin, flexural strength and moduli. For three HV-GICs and one C-GIC, significant differences (p<0.05) in gap-incidence were observed between polishing immediately and after one-day storage. In the former case, 80â100 gaps were found. In the latter case, only 9â21 gaps were observed. For all materials, their shear-bond-strengths, flexural strength and moduli increased significantly after 24-hour storage.</p
Class I Gap-formation in Highly-viscous Glass-ionomer Restorations: Delayed vs Immediate Polishing
This in vitro study evaluated the effects of delayed versus immediate polishing to permit maturation of interfacial gap-formation around highly viscous conventional glass-ionomer cement (HV-GIC) in Class I restorations, together with determining the associated mechanical properties. Cavity preparations were made on the occlusal surfaces of premolars. Three HV-GICs (Fuji IX GP, GlasIonomer FX-II and Ketac Molar) and one conventional glass-ionomer cement (C-GIC, Fuji II, as a control) were studied, with specimen subgroups (n=10) for each property measured. After polishing, either immediately (six minutes) after setting or after 24 hours storage, the restored teeth were sectioned in a mesiodistal direction through the center of the model Class I restorations. The presence or absence of interfacial-gaps was measured at 1000Ă magnification at 14 points (each 0.5-mm apart) along the cavity restoration interface (n=10; total points measured per group = 140). Marginal gaps were similarly measured in Teflon molds as swelling data, together with shear-bond-strength to enamel and dentin, flexural strength and moduli. For three HV-GICs and one C-GIC, significant differences (p<0.05) in gap-incidence were observed between polishing immediately and after one-day storage. In the former case, 80â100 gaps were found. In the latter case, only 9â21 gaps were observed. For all materials, their shear-bond-strengths, flexural strength and moduli increased significantly after 24-hour storage.</p
Revisiting CoRoT RR Lyrae stars: detection of period doubling and temporal variation of additional frequencies
We search for signs of period doubling in CoRoT RR Lyrae stars. The
occurrence of this dynamical effect in modulated RR Lyrae stars might help us
to gain more information about the mysterious Blazhko effect. The temporal
variability of the additional frequencies in representatives of all subtypes of
RR Lyrae stars is also investigated. We pre-process CoRoT light curves by
applying trend and jump correction and outlier removal. Standard Fourier
technique is used to analyze the frequency content of our targets and follow
the time dependent phenomena. The most comprehensive collection of CoRoT RR
Lyrae stars, including new discoveries is presented and analyzed. We found
alternating maxima and in some cases half-integer frequencies in four CoRoT
Blazhko RR Lyrae stars, as clear signs of the presence of period doubling. This
reinforces that period doubling is an important ingredient to understand the
Blazhko effect - a premise we derived previously from the Kepler RR Lyrae
sample. As expected, period doubling is detectable only for short time
intervals in most modulated RRab stars. Our results show that the temporal
variability of the additional frequencies in all RR Lyrae sub-types is
ubiquitous. The ephemeral nature and the highly variable amplitude of these
variations suggest a complex underlying dynamics of and an intricate interplay
between radial and possibly nonradial modes in RR Lyrae stars. The omnipresence
of additional modes in all types of RR Lyrae - except in non-modulated RRab
stars - implies that asteroseismology of these objects should be feasible in
the near future (Abridged).Comment: 20 pages, 13 figures, accepted for publication in A&
The CoRoT star 105288363: strong cycle to cycle changes of the Blazhko modulation
We present the analysis of the CoRoT star 105288363, a new Blazhko RR Lyrae
star of type RRab (f0 = 1.7623 c/d), observed with the CoRoT space craft during
the second long run in direction of the galactic center (LRc02, time base 145
d). The CoRoT data are characterized by an excellent time sampling and a low
noise amplitude of 0.07 mmag in the 2-12 c/d range and allow us to study not
only the fine details of the variability of the star but also long-term changes
in the pulsation behaviour and the stability of the Blazhko cycle. We use,
among other methods, standard Fourier analysis techniques and O-C diagrams to
investigate the pulsational behavior of the Blazhko star 105288363. In addition
to the frequency pattern expected for a Blazhko RR Lyrae star, we find an
independent mode (f1 = 2.984 c/d) showing a f0/f1 ratio of 0.59 which is
similar to that observed in other Blazhko RR Lyrae stars. The bump and hump
phenomena are also analysed, with their variations over the Blazhko cycle. We
carefully investigated the strong cycle-to-cycle changes in the Blazhko
modulation (PB = 35.6 d), which seem to happen independently and partly
diametrically in the amplitude and the phase modulation. Furthermore, the
phasing between the two types of modulation is found to change during the
course of the observations.Comment: 15 pages, 8 figures, accepted for publication in MNRA
Particle size as controlling factor of soil microaggregate formation
Aggregates are formed when soil particles connect to larger secondary units. Stable microaggregates in soils are supposed to consist of close associations of Fe-oxides and clay minerals with both components being attracted by electrostatic forces between the oppositely charged particles. However, the geometric preconditions for the formation of stable associations between Fe oxides and clay minerals are poorly known. Therefore, our goal was to determine geometrical constraints resulting from particle size and morphology likely impeding optimum arrangement of particles for shielding of charges during aggregate formation. Aggregation kinetics was determined for nine combinations of each three particle size fractions of goethite and mica in a Zetasizer at pH 6. Experiments were conducted using needle-shape goethites synthesized at 4, 20, and 60°C (lengths of 0.42, 0.46 and 0.84 ”m, specific surface areas (SSA) of 87, 75, and 60 mÂČ/g, respectively) and ground platy muscovite separated in fine, medium and coarse clay (diameters of 0.16, 0.80, and 2.9 ”m, SSA of 182, 100, and 27 mÂČ/g, respectively). For five combinations even smallest additions of goethite to muscovite facilitated aggregation. By further additions of goethite maximum aggregate sizes up to 5.6 ”m were obtained, the respective mixing ratio strongly depending on the type of combination. After that sizes declined. For medium and coarse-sized muscovite, goethite amendments >18% did not facilitate aggregation, indicating the dominance of repulsive forces. In contrast, for fine-sized muscovite aggregation was facilitated up to an addition of 63% fine-sized goethite and of 90% coarse-sized goethite. Here also biggest aggregate sizes were obtained. Based on all examined size fraction combinations, our results suggest a strong impact of particle size on aggregation. Whereas all combinations with fine-sized muscovite facilitated aggregation at very different mixing ratios, the amendment of the finest fraction of goethite to medium- and coarse-sized muscovite facilitated aggregation at small additions only. Aggregation was favored for evenly sized combinations. The quantification of surface charge density of minerals and calculation of charge balances of the combinations is in progress and will help interpreting the observed aggregation patterns. For soils it is likely that aggregation by electrostatic interactions occurs only at certain mineral mixing ratios highly depending on particle morphology
- âŠ