220 research outputs found
Analytische technieken voor niet-lineaire differentiaalvergelijkingen, die optreden in halfgeleider berekeningen
Tracing snowlines and C/O ratio in a planet-hosting disk: ALMA molecular line observations towards the HD169142 disk
The composition of a forming planet is set by the material it accretes from
its parent protoplanetary disk. Therefore, it is crucial to map the chemical
make-up of the gas in disks to understand the chemical environment of planet
formation. This paper presents molecular line observations taken with the
Atacama Large Millimeter/submillimeter Array of the planet-hosting disk around
the young star HD 169142. We detect N2H+, CH3OH, [CI], DCN, CS, C34S, 13CS,
H2CS, H2CO, HC3N and c-C3H2 in this system for the first time. Combining these
data with the recent detection of SO and previously published DCO+ data, we
estimate the location of H2O and CO snowlines and investigate radial variations
in the gas phase C/O ratio. We find that the HD 169142 disk has a relatively
low N2H+ flux compared to the disks around Herbig stars HD 163296 and MWC 480
indicating less CO freeze-out and place the CO snowline beyond the millimetre
disk at ~150 au. The detection of CH3OH from the inner disk is consistent with
the H2O snowline being located at the edge of the central dust cavity at ~20
au. The radially varying CS/SO ratio across the proposed H2O snowline location
is consistent with this interpretation. Additionally, the detection of CH3OH in
such a warm disk adds to the growing evidence supporting the inheritance of
complex ices in disks from the earlier, colder stages of star formation.
Finally, we propose that the giant HD 169142 b located at 37 au is forming
between the CO2 and H2O snowlines where the local elemental make of the gas is
expected to have C/O=1.0.Comment: Accepted A&A 13th August 202
Surface morphology and agglutinability with concanavalin A in normal and transformed murine fibroblasts.
Elevated micro-topography boosts growth rates in <i>Salicornia procumbens</i> by amplifying a tidally driven oxygen pump:Implications for natural recruitment and restoration
• Background and Aims: The growth rate of pioneer species is known to be a critical component determining recruitment success of marsh seedlings on tidal flats. By accelerating growth, recruits can reach a larger size at an earlier date, which reduces the length of the disturbance-free window required for successful establishment. Therefore, the pursuit of natural mechanisms that accelerate growth rates at a local scale may lead to a better understanding of the circumstances under which new establishment occurs, and may suggest new insights with which to perform restoration. This study explores how and why changes in local sediment elevation modify the growth rate of recruiting salt marsh pioneers. • Methods: A mesocosm experiment was designed in which the annual salt marsh pioneer Salicornia procumbens was grown over a series of raised, flat and lowered sediment surfaces, under a variety of tidal inundation regimes and in vertically draining or un-draining sediment. Additional physical tests quantified the effects of these treatments on sediment water-logging and oxygen dynamics, including the use of a planar optode experiment. • Key Results: In this study, the elevation of sediment micro-topography by 2 cm was the overwhelming driver of plant growth rates. Seedlings grew on average 25 % faster on raised surfaces, which represented a significant increase when compared to other groups. Changes in growth aligned well with the amplifying effect of raised sediment beds on a tidally episodic oxygenation process wherein sediment pore spaces were refreshed by oxygen-rich water at the onset of high tide. • Conclusions: Overall, the present study suggests this tidally driven oxygen pump as an explanation for commonly observed natural patterns in salt marsh recruitment near drainage channels and atop raised sediment mounds and reveals a promising way forward to promote the establishment of pioneers in the field
Efficiënt met mineralen door KringloopWijzer
De ontwikkeling van de KringloopWijzer is in volle gang. Via een bedrijfsspecifieke rekenwijze kunnen opbrengsten en verliezen van het melkveebedrijf betrouwbaar worden vastgesteld. Dit vormt niet alleen een belangrijke basis voor verbetering van de bedrijfsvoering, maar met dit kengetallenoverzicht kan een veehouder ook verantwoording afleggen over zijn milieuprestatie
Controlling the nitrogen environment for optimal Rhodomonas salina production
The microalga Rhodomonas salina is a widely used species for rearing live feed organisms in the aquaculture feed market. A species-specific medium is an essential step towards enhancing productivity and decreasing production costs for microalgae cultivation. However, relevant aspects of medium composition such as nitrogen source and elemental ratio have not yet been characterized for this alga. This study aimed to optimize the following three aspects of culture media: 1) optimal ratio between nitrogen and phosphorus (N:P ratio); 2) preferred source of nitrogen; and 3) tolerance of R. salina towards free ammonia. To investigate this, we conducted a series of controlled laboratory experiments in shake flasks. Our experiments revealed a 45% increase in growth rate when an N:P ratio of 15:1 was used compared to the standard ratio of 25:1. Ammonium and nitrate were equally well accepted as a nitrogen source, however, a mix of ammonium and nitrate resulted in significant growth reduction. Free ammonia did not affect growth of the alga at the tested concentrations of up to 5 mg ammonia–nitrogen L−1. We conclude that for optimal R. salina cultivation, an N:P ratio of 15:1 is strongly preferred, as it leads to a significant increase in growth rate. Further, media with a single source of nitrogen promote faster growth over media with mixed sources, and ammonium may safely be used as a nitrogen source, since R. salina tolerates certain levels of free ammonia. Overall, this work provides insights into the optimal cultivation conditions for R. salina, allowing for more efficient and reliable production of this relevant species
Population synthesis of accreting white dwarfs: Rates and evolutionary pathways of H and He novae
Novae are some of the most commonly detected optical transients and have the
potential to provide valuable information about binary evolution. Binary
population synthesis codes have emerged as the most effective tool for
modelling populations of binary systems, but such codes have traditionally
employed greatly simplified nova physics, precluding detailed study. In this
work, we implement a model treating H and He novae as individual events into
the binary population synthesis code \binaryc. This treatment of novae
represents a significant improvement on the `averaging' treatment currently
employed in modern population synthesis codes. We discuss the evolutionary
pathways leading to these phenomena and present nova event rates and
distributions of several important physical parameters. Most novae are produced
on massive white dwarfs, with approximately 70 and 55 per cent of nova events
occurring on O/Ne white dwarfs for H and He novae respectively. Only 15 per
cent of H-nova systems undergo a common-envelope phase, but these systems are
responsible for the majority of H nova events. All He-accreting He-nova systems
are considered post-common-envelope systems, and almost all will merge with
their donor star in a gravitational-wave driven inspiral. We estimate the
current annual rate of novae in M31 (Andromeda) to be approximately
for H novae, underpredicting the current observational estimate of
, and for He novae. When varying common-envelope
parameters, the H nova rate varies between 20 and 80 events per year.Comment: Accepted, MNRAS. 7 Jun 2020: Minor correction regarding AM CVn masses
at period bounce, courtesy of P. Neuteufe
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