228 research outputs found
Course report: Climate change adaptation in agriculture and natural resource management - Integrating climate change in policy making and programming for sustainable development
At the request of the Ministry of Agriculture, Nature and Food Quality (LNV) in the Netherlands, Wageningen UR1 has initiated a support programme for climate change adaptation in Eastern Africa in 2008. In partnership with ASARECA2, IUCN – EARO3 and RUFORUM4 a scoping workshop and follow-up were organised. The focus was on capacities needed to better integrated climate change adaptation responses into agricultural, rural development and natural resources policy processes. The initiative led, among others, to the development of a new training course in 2009, implemented by the partnership, in collaboration with HoA-REC5 at Addis Ababa University, Ethiopia. The regional training on Climate Change Adaptation in agriculture and NRM took place from 15 to 26 June 2009 in Addis Ababa. It was attended by 26 participants from Ethiopia (20), Uganda (3), Kenya (2) and Tanzania (1). Participants were drawn from universities, agricultural research institutes, non-governmental organisations and government departments. The course was coordinated and facilitated by a team from HoA-REC and Wageningen UR, complemented by presenters and lecturers from various universities and institutes, such as Prof. Richard Odingo (University of Nairobi), Dr. Jan Verhagen (Wageningen UR), Dr. Gebru Jember (National Meteorological Agency, Ethiopia), and Dr. Lulseged Tamene (Addis Ababa University)
Ice and gas in protostellar clouds and planet-forming disks: a combined laboratory and observational study
This thesis takes steps toward understanding the interaction between gas-phase and solid-state molecules in star- and planet-forming regions. Chapter 1 and 2 provide the reader with an introduction and in-depth description of methods used in subsequent chapters. Chapter 3 and 4 present the spectroscopic infrared characterization of acetaldehyde, dimethyl ether, ethanol, and methyl formate in the solid state, both pure and mixed in astronomically relevant matrices. This characterization will allow for probing of the solid-state organic inventory of star- and planet-forming regions with the upcoming James Webb Space Telescope. Interferometric observations of the protoplanetary disk around TW Hya with the Atacama Large Millimeter/submillimeter Array are presented in Chapter 5. These results hint that the observed gas-phase formaldehyde is formed in the gas phase, contrary to the generally accepted solid-state formation. Chapter 6 provides an insight to the interaction between gas-phase carbon monoxide and solid-state hydroxyl radicals on the surface of vacuum-UV irradiated water ice. Even tough residence times of carbon monoxide are short, they are sufficient to allow reactions with hydroxyl radicals and produce carbon dioxide. This process could explain the lack of gas-phase carbon monoxide in protoplanetary disks and the presence of carbon dioxide mixed in solid-state water.Instrumentatio
Substrate-Assisted Catalysis Unifies Two Families of Chitinolytic Enzymes
Hen egg-white lysozyme has long been the paradigm for enzymatic glycosyl hydrolysis with retention of configuration, with a protonated carboxylic acid and a deprotonated carboxylate participating in general acid-base catalysis. In marked contrast, the retaining chitin degrading enzymes from glycosyl hydrolase families 18 and 20 all have a single glutamic acid as the catalytic acid but lack a nucleophile on the enzyme. Both families have a catalytic (βα)8-barrel domain in common. X-ray structures of three different chitinolytic enzymes complexed with substrates or inhibitors identify a retaining mechanism involving a protein acid and the carbonyl oxygen atom of the substrate’s C2 N-acetyl group as the nucleophile. These studies unambiguously demonstrate the distortion of the sugar ring toward a sofa conformation, long postulated as being close to that of the transition state in glycosyl hydrolysis.
The formation of CO through consumption of gas-phase CO on vacuum-UV irradiated water ice
[Abridged] Observations of protoplanetary disks suggest that they are
depleted in gas-phase CO. It has been posed that gas-phase CO is chemically
consumed and converted into less volatile species through gas-grain processes.
Observations of interstellar ices reveal a CO component within HO ice
suggesting co-formation. The aim of this work is to experimentally verify the
interaction of gas-phase CO with solid-state OH radicals above the sublimation
temperature of CO. Amorphous solid water (ASW) is deposited at 15 K and
followed by vacuum-UV (VUV) irradiation to dissociate HO and create OH
radicals. Gas-phase CO is simultaneously admitted and only adsorbs with a short
residence time on the ASW. Products in the solid state are studied with
infrared spectroscopy and once released into the gas phase with mass
spectrometry. Results show that gas-phase CO is converted into CO, with an
efficiency of 7-27%, when interacting with VUV irradiated ASW. Between 40 and
90 K, CO production is constant, above 90 K, O production takes over.
In the temperature range of 40-60 K, the CO remains in the solid state,
while at temperatures 70 K the formed CO is released into the gas
phase. We conclude that gas-phase CO reacts with solid-state OH radicals above
its sublimation temperature. This gas-phase CO and solid-state OH radical
interaction could explain the observed CO embedded in water-rich ices. It
may also contribute to the observed lack of gas-phase CO in planet-forming
disks, as previously suggested. Our experiments indicate a lower water ice
dissociation efficiency than originally adopted in model descriptions of
planet-forming disks and molecular clouds. Incorporation of the reduced water
ice dissociation and increased binding energy of CO on a water ice surfaces in
these models would allow investigation of this gas-grain interaction to its
full extend.Comment: Accepted for publication in Astronomy & Astrophysic
Infra-red spectra of complex organic molecules in astronomically relevant ice matrices
Laboratory astrophysics and astrochemistr
An inherited complex organic molecule reservoir in a warm planet-hosting disk
Quantifying the composition of the material in protoplanetary disks is essential to determining the potential for exoplanetary systems to produce and support habitable environments. When considering potential habitability, complex organic molecules are relevant, key among which is methanol (CH3OH). Methanol primarily forms at low temperatures via the hydrogenation of CO ice on the surface of icy dust grains and is a necessary basis for the formation of more complex species such as amino acids and proteins. We report the detection of CH3OH in a disk around a young, luminous A-type star, HD 100546. This disk is warm and therefore does not host an abundant reservoir of CO ice. We argue that the CH3OH cannot form in situ, and hence that this disk has probably inherited complex-organic-molecule-rich ice from an earlier cold dark cloud phase. This is strong evidence that at least some interstellar organic material survives the disk-formation process and can then be incorporated into forming planets, moons and comets. Therefore, crucial pre-biotic chemical evolution already takes place in dark star-forming clouds
The formation of peptide-like molecules on interstellar dust grains
Molecules with an amide functional group resemble peptide bonds, the
molecular bridges that connect amino acids, and may thus be relevant in
processes that lead to the formation of life. In this study, the solid state
formation of some of the smallest amides is investigated in the laboratory. To
this end, CH:HNCO ice mixtures at 20 K are irradiated with far-UV
photons, where the radiation is used as a tool to produce the radicals required
for the formation of the amides. Products are identified and investigated with
infrared spectroscopy and temperature programmed desorption mass spectrometry.
The laboratory data show that NHCHO, CHNCO, NHC(O)NH,
CHC(O)NH and CHNH can simultaneously be formed. The
NHCO radical is found to be key in the formation of larger amides. In
parallel, ALMA observations towards the low-mass protostar IRAS 16293-2422B are
analysed in search of CHNHCHO (N-methylformamide) and
CHC(O)NH (acetamide). CHC(O)NH is tentatively detected
towards IRAS 16293-2422B at an abundance comparable with those found towards
high-mass sources. The combined laboratory and observational data indicates
that NHCHO and CHC(O)NH are chemically linked and form in the
ice mantles of interstellar dust grains. A solid-state reaction network for the
formation of these amides is proposed.Comment: Accepted for publication in MNRA
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