| 1. |
- Fomalont, E. B., et al.
(författare)
-
THE 2014 ALMA LONG BASELINE CAMPAIGN: AN OVERVIEW
- 2015
-
Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 808:1
-
Tidskriftsartikel (refereegranskat)abstract
- A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to make accurate images with resolutions of tens of milliarcseconds, which at submillimeter (submm) wavelengths requires baselines up to similar to 15 km. To develop and test this capability, a Long Baseline Campaign (LBC) was carried out from 2014 September to late November, culminating in end-to-end observations, calibrations, and imaging of selected Science Verification (SV) targets. This paper presents an overview of the campaign and its main results, including an investigation of the short-term coherence properties and systematic phase errors over the long baselines at the ALMA site, a summary of the SV targets and observations, and recommendations for science observing strategies at long baselines. Deep ALMA images of the quasar 3C 138 at 97 and 241 GHz are also compared to VLA 43 GHz results, demonstrating an agreement at a level of a few percent. As a result of the extensive program of LBC testing, the highly successful SV imaging at long baselines achieved angular resolutions as fine as 19 mas at similar to 350 GHz. Observing with ALMA on baselines of up to 15 km is now possible, and opens up new parameter space for submm astronomy.
|
|
| 2. |
|
|
| 3. |
- Wilke, T., et al.
(författare)
-
Deep drilling reveals massive shifts in evolutionary dynamics after formation of ancient ecosystem
- 2020
-
Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 6:40
-
Tidskriftsartikel (refereegranskat)abstract
- The scarcity of high-resolution empirical data directly tracking diversity over time limits our understanding of speciation and extinction dynamics and the drivers of rate changes. Here, we analyze a continuous species-level fossil record of endemic diatoms from ancient Lake Ohrid, along with environmental and climate indicator time series since lake formation 1.36 million years (Ma) ago. We show that speciation and extinction rates nearly simultaneously decreased in the environmentally dynamic phase after ecosystem formation and stabilized after deep-water conditions established in Lake Ohrid. As the lake deepens, we also see a switch in the macroevolutionary trade-off, resulting in a transition from a volatile assemblage of short-lived endemic species to a stable community of long- lived species. Our results emphasize the importance of the interplay between environmental/climate change, ecosystem stability, and environmental limits to diversity for diversification processes. The study also provides a new understanding of evolutionary dynamics in long-lived ecosystems.
|
|
| 4. |
- Ayasse, Manfred, et al.
(författare)
-
Evolution of reproductive strategies in the sexually deceptive orchid Ophrys sphegodes: How does flower-specific variation of odor signals influence reproductive success?
- 2000
-
Ingår i: Evolution. - 1558-5646. ; 54:6, s. 1995-2006
-
Tidskriftsartikel (refereegranskat)abstract
- The orchid Ophrys sphegodes Miller is pollinated by sexually excited males of the solitary bee Andrena nigroaenea, which are lured to the flowers by visual cues and volatile semiochemicals. In O. sphegodes, visits by pollinators are rare. Because of this low frequency of pollination, one would expect the evolution of strategies that increase the chance that males will visit more than one flower on the same plant; this would increase the number of pollination events on a plant and therefore the number of seeds produced. Using gas chromatography-mass spectrometry (GC-MS) analyses, we identified more than 100 compounds in the odor bouquets of labellum extracts from O. sphegodes; 24 compounds were found to be biologically active in male olfactory receptors based on gas chromatography with electroantennographic detection (GC-EAD). Gas chromatography (GC) analyses of odors from individual flowers showed less intraspecific variation in the odor bouquets of the biologically active compounds as compared to nonactive compounds. This can be explained by a higher selective pressure on the pollinator-attracting communication signal. Furthermore, we found a characteristic variation in the GC-EAD active esters and aldehydes among flowers of different stem positions within an inflorescence and in the n-alkanes and n-alkenes among plants from different populations. In our behavioral field tests, we showed that male bees learn the odor bouquets of individual flowers during mating attempts and recognize them in later encounters. Bees thereby avoid trying to mate with flowers they have visited previously, but do not avoid other flowers either of a different or the same plant. By varying the relative proportions of saturated esters and aldehydes between flowers of different stem positions, we demonstrated that a plant may take advantage of the learning abilities of the pollinators and influence flower visitation behavior. Sixty-seven percent of the males that visited one flower in an inflorescence returned to visit a second flower of the same inflorescence. However, geitonogamy is prevented and the likelihood of cross-fertilization is enhanced by the time required for the pollinium deposited on the pollinator to complete its bending movement, which is necessary for pollination to occur. Cross-fertilization is furthermore enhanced by the high degree of odor variation between plants. This variation minimizes learned avoidance of the flowers and increases the likelihood that a given pollinator would visit several to many different plants within a population.
|
|
| 5. |
- Guaita, Lucia, et al.
(författare)
-
Magellan/MMIRS near-infrared multi-object spectroscopy of nebular emission from star-forming galaxies at 2 < z < 3
- 2013
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 551, s. A93-
-
Tidskriftsartikel (refereegranskat)abstract
- Aims. To investigate the ingredients, which allow star-forming galaxies to present Ly alpha line in emission, we studied the kinematics and gas phase metallicity of the interstellar medium. Methods. We used multi-object near-infrared spectroscopy with Magellan/MMIRS to study nebular emission from z similar or equal to 2-3 star-forming galaxies discovered in three MUSYC fields. Results. We detected emission lines from four active galactic nuclei and 13 high-redshift star-forming galaxies, including H alpha lines down to a flux of (4 +/- 1)E-17 erg s(-1) cm(-2). This yielded seven new redshifts. The most common emission line detected is [OIII]5007, which is sensitive to metallicity. We were able to measure metallicity (Z) for two galaxies and to set upper (lower) limits for another two (two). The metallicity values are consistent with 0.3 < Z/Z(circle dot) < 1.2, 12 + log (O/H) similar to 8.2-8.8. Comparing the Ly alpha central wavelength with the systemic redshift, we find Delta(vLy alpha-[OIII]5007) = 70 270 km s(-1). Conclusions. High-redshift star-forming galaxies, Ly alpha emitting (LAE) galaxies, and H alpha emitters appear to be located in the low mass, high star-formation rate (SFR) region of the SFR versus stellar mass diagram, confirming that they are experiencing burst episodes of star formation, which are building up their stellar mass. Their metallicities are consistent with the relation found for z <= 2.2 galaxies in the Z versus stellar mass plane. The measured Delta(vLy alpha[OIII]5007) values imply that outflows of material, driven by star formation, could be present in the z similar to 2 3 LAEs of our sample. Comparing with the literature, we note that galaxies with lower metallicity than ours are also characterized by similar Delta(vLy alpha[OIII]5007) velocity off sets. Strong F([OIII]5007) is detected in many Ly alpha emitters. Therefore, we propose the F(Ly alpha)/F([OIII]5007) flux ratio as a tool for the study of high-redshift galaxies; while influenced by metallicity, ionization, and Ly alpha radiative transfer in the ISM, it may be possible to calibrate this ratio to primarily trace one of these effects.
|
|
| 6. |
- Nowaczyk, N. R., et al.
(författare)
-
Chronology of Lake El'gygytgyn sediments - a combined magnetostratigraphic, palaeoclimatic and orbital tuning study based on multi-parameter analyses
- 2013
-
Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 9:6, s. 2413-2432
-
Tidskriftsartikel (refereegranskat)abstract
- A 318-metre-long sedimentary profile drilled by the International Continental Scientific Drilling Program (ICDP) at Site 5011-1 in Lake El'gygytgyn, Far East Russian Arctic, has been analysed for its sedimentologic response to global climate modes by chronostratigraphic methods. The 12 km wide lake is sited off-centre in an 18 km large crater that was created by the impact of a meteorite 3.58 Ma ago. Since then sediments have been continuously deposited. For establishing their chronology, major reversals of the earth's magnetic field provided initial tie points for the age model, confirming that the impact occurred in the earliest geomagnetic Gauss chron. Various stratigraphic parameters, reflecting redox conditions at the lake floor and climatic conditions in the catchment were tuned synchronously to Northern Hemisphere insolation variations and the marine oxygen isotope stack, respectively. Thus, a robust age model comprising more than 600 tie points could be defined. It could be shown that deposition of sediments in Lake El'gygytgyn occurred in concert with global climatic cycles. The upper similar to 160m of sediments represent the past 3.3 Ma, equivalent to sedimentation rates of 4 to 5 cm ka(-1), whereas the lower 160m represent just the first 0.3 Ma after the impact, equivalent to sedimentation rates in the order of 45 cm ka(-1). This study also provides orbitally tuned ages for a total of 8 tephras deposited in Lake El'gygytgyn.
|
|
| 7. |
|
|
| 8. |
- Schiestl, F. P., et al.
(författare)
-
Orchid pollination by sexual swindle [5]
- 1999
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 399:6735, s. 421-422
-
Tidskriftsartikel (refereegranskat)
|
|
| 9. |
- Thunberg, S., et al.
(författare)
-
Dose reduction in mammography with photon counting imaging
- 2004
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. ; , s. 457-465
-
Konferensbidrag (refereegranskat)abstract
- The purpose of this study was to investigate if the glandular dose to the breast in mammography can significantly be reduced without compromising image quality, when using photon counting technology, in a multi-slit scanning photon counting detector, compared to a conventional film mammography system and commercial available digital mammography systems with TFT-array detectors. A CDMAM phantom study, with two different thicknesses of additional PMMA absorber, 4 cm and 7 cm respectively, has shown that multi-slit scanning photon counting detector technology can reduce the dose, without reducing the image quality. This comparison was made to two commercial available digital mammography systems Senographe 2000D (from GEMS) and Selenia (from Lorad). The results show that dose can be reduced with 63% to 77%, depending on object thickness, when using XCT for mammography. This dose reduction has also been verified clinically through a small pilot study with patients and specimen, where the comparison was made between XCT and film.
|
|
| 10. |
- Tröger, Armin, et al.
(författare)
-
Tetranorsesquiterpenoids as attractants of yucca moths to yucca flowers
- 2021
-
Ingår i: Journal of Chemical Ecology. - : Springer Science and Business Media LLC. - 0098-0331 .- 1573-1561. ; 47:12, s. 1025-1041
-
Tidskriftsartikel (refereegranskat)abstract
- The obligate pollination mutualism between Yucca and yucca moths is a classical example of coevolution. Oviposition and active pollination by female yucca moths occur at night when Yucca flowers are open and strongly scented. Thus, floral volatiles have been suggested as key sensory signals attracting yucca moths to their host plants, but no bioactive compounds have yet been identified. In this study, we showed that both sexes of the pollinator moth Tegeticula yuccasella are attracted to the floral scent of the host Yucca filamentosa. Chemical analysis of the floral headspace from six Yucca species in sections Chaenocarpa and Sarcocarpa revealed a set of novel tetranorsesquiterpenoids putatively derived from (E)-4,8-dimethyl-1,3,7-nonatriene. Their structure elucidation was accomplished by NMR analysis of the crude floral scent sample of Yucca treculeana along with GC/MS analysis and confirmed by total synthesis. Since all these volatiles are included in the floral scent of Y. filamentosa, which has been an important model species for understanding the pollination mutualism, we name these compounds filamentolide, filamentol, filamental, and filamentone. Several of these compounds elicited antennal responses in pollinating (Tegeticula) and non-pollinating (Prodoxus) moth species upon stimulation in electrophysiological recordings. In addition, synthetic (Z)-filamentolide attracted significant numbers of both sexes of two associated Prodoxus species in a field trapping experiment. Highly specialized insect-plant interactions, such as obligate pollination mutualisms, are predicted to be maintained through “private channels” dictated by specific compounds. The identification of novel bioactive tetranorsesquiterpenoids is a first step in testing such a hypothesis in the Yucca-yucca moth interaction.
|
|
