Thermal Band Heating for Intra-Row Weed Control

Surface steaming of soil is a very energy-intensive process, and consequently, efforts have been made to develop a machine for narrow-band steaming of the soil under and around rows of cultivated plants prior to seeding. The use of this machine may achieve up to 90% energy savings, and will also reduce the amount of damage to the flora and fauna. A special test rig has been developed with the objective of obtaining new information about narrow-band soil steaming. For a detailed analysis of the temperature profile in a cross-section of the processed band, an apparatus has been developed especially to record the temperatures obtained at 63 locations and at seven levels across the ditch. On the basis of the results from the test rig, a prototype band-steamer for field use has been developed. Tests have shown that soil temperatures exceeding 70C will be needed to protect against germination of weed seeds. For band heating such a treatment in 50 cm rows requires about 5.8 GJ/ha

Tracing the physical and chemical evolution of low-mass protostars

LEI Universiteit LeidenUBL - phd migration 201

Warm water deuterium fractionation in IRAS 16293-2422. The high-resolution ALMA and SMA view

Context. Measuring the water deuterium fractionation in the inner warm regions of low-mass protostars has so far been hampered by poor angular resolution obtainable with single-dish ground- and space-based telescopes. Observations of water isotopologues using (sub)millimeter wavelength interferometers have the potential to shed light on this matter. Aims: To measure the water deuterium fractionation in the warm gas of the deeply-embedded protostellar binary IRAS 16293-2422. Methods: Observations toward IRAS 16293-2422 of the 5$_{3,2}$ - 4$_{4,1}$ transition of H$_{2}$$^{18}$O at 692.07914 GHz from Atacama Large Millimeter/submillimeter Array (ALMA) as well as the 3$_{1,3}$ - 2$_{2,0}$ of H$_{2}$$^{18}$O at 203.40752 GHz and the 3$_{1,2}$ - 2$_{2,1}$ transition of HDO at 225.89672 GHz from the Submillimeter Array (SMA) are presented. Results: The 692 GHz H$_{2}$$^{18}$O line is seen toward both components of the binary protostar. Toward one of the components, ''source B'', the line is seen in absorption toward the continuum, slightly red-shifted from the systemic velocity, whereas emission is seen off-source at the systemic velocity. Toward the other component, ''source A'', the two HDO and H$_{2}$$^{18}$O lines are detected as well with the SMA. From the H$_{2}$$^{18}$O transitions the excitation temperature is estimated at 124 {plusmn} 12 K. The calculated HDO/H$_{2}$O ratio is (9.2 {plusmn} 2.6) { imes} 10$^{-4}$ - significantly lower than previous estimates in the warm gas close to the source. It is also lower by a factor of ~{}5 than the ratio deduced in the outer envelope. Conclusions: Our observations reveal the physical and chemical structure of water vapor close to the protostars on solar-system scales. The red-shifted absorption detected toward source B is indicative of infall. The excitation temperature is consistent with the picture of water ice evaporation close to the protostar. The low HDO/H$_{2}$O ratio deduced here suggests that the differences between the inner regions of the protostars and the Earth's oceans and comets are smaller than previously thought. Appendix A is available in electronic form at http://www.aanda.or

Star and Planet Formation with ALMA: an Overview

Submillimeter observations with ALMA will be the essential next step in our understanding of how stars and planets form. Key projects range from detailed imaging of the collapse of pre-stellar cores and measuring the accretion rate of matter onto deeply embedded protostars, to unravelling the chemistry and dynamics of high-mass star-forming clusters and high-spatial resolution studies of protoplanetary disks down to the 1 AU scale.Comment: Invited review, 8 pages, 5 figures; to appear in the proceedings of "Science with ALMA: a New Era for Astrophysics". Astrophysics & Space Science, in pres

Testing Grain-Surface Chemistry in Hot Core Regions

Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe

Molecular inventories and chemical evolution of low-mass protostellar envelopes

Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe

On the origin of H2CO abundance enhancements in low-mass protostars

Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe

A `starless' core that isn't: detection of a source in the L1014 dense core with the Spitzer Space Telescope

Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe

Does IRAS 16293-2422 have a hot core? Chemical inventory and abundance changes in its protostellar environment

Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe