268 research outputs found
Evaluation of model systems for the study of protein association / incorporation of Beta-Methylamino-L-Alanine (BMAA)
β-methylamino-L-alanine (BMAA) is thought to be a contributing factor of Amyotrophic Lateral Sclerosis-Parkinsonism Dementia Complex (ALS/PDC). It has been shown that the levels of toxin ingestion by humans are too low to cause disease. However, it has recently been theorized that this toxin is bioaccumulated within cells. Via a process of slow release from this reservoir, the BMAA is able to bring about neurotoxicity. Mechanisms of uptake and bioaccumulation of BMAA have been proposed in several publications; however the mechanism of protein incorporation of BMAA has not yet been identified. Identifying suitable model systems would be a prerequisite in order for future studies on BMAA protein incorporation. Three specific models were therefore chosen for investigation; mammalian cell lines including C2C12 and HT29, a prokaryotic (E. coli) expression system and yeast cells. The cytotoxity of BMAA was established for the mammalian cell lines and further investigation of BMAA incorporation into cellular proteins was performed on all three above mentioned models. Samples were run on HPLC-MS in order to determine uptake of BMAA into cells or lack thereof. Results indicate negligible cytotoxicity as measured by MTT and CellTitre Blue assays, limited uptake and protein incorporation of BMAA within the prokaryotic model and insignificant uptake of BMAA by yeast cells. Although the uptake of BMAA in the prokaryotic model was not extensive, there was indeed uptake. BMAA was not only taken up into the cells but was also observed in inclusion body protein samples after hydrolysis. After further investigation and use, this model could very well provide researchers with information pertaining to the mechanism of association of BMAA with proteins. Although the other models provided negative results, this research was valuable in the sense that one can narrow down the number of possible model systems available. Also, in seeking models for studying protein association/incorporation, the use of the final target cell is not relevant or necessary as the purpose of the research was to identify a model system in which the mechanism of protein association/incorporation can, in future, be studied
Completion of a SCUBA survey of Lynds dark clouds and implications for low-mass star formation
We have carried out a survey of optically-selected dark clouds using the
bolometer array SCUBA on the James Clerk Maxwell Telescope, at 850 microns
wavelength. The survey covers a total of 0.5 square degrees and is unbiased
with reference to cloud size, star formation activity, or the presence of
infrared emission. Several new protostars and starless cores have been
discovered; the protostars are confirmed through the detection of their
accompanying outflows in CO(2-1) emission. The survey is believed to be
complete for Class 0 and Class I protostars, and yields two important results
regarding the lifetimes of these phases. First, the ratio of Class 0 to Class
protostars in the sample is roughly unity, very different from the 1:10 ratio
that has previously been observed for the rho Ophiuchi star-forming region.
Assuming star formation to be a homogeneous process in the dark clouds, this
implies that the Class 0 lifetime is similar to the Class I phase, which from
infrared surveys has been established to be approximately 200,000 yr. It also
suggests there is no rapid initial accretion phase in Class 0 objects. A burst
of triggered star formation some 100,000 yr ago can explain the earlier results
for rho Ophiuchus. Second, the number of starless cores is approximately twice
that of the total number of protostars, indicating a starless core lifetime of
approximately 800,000 yr. These starless cores are therefore very short-lived,
surviving only two or three free-fall times. This result suggests that, on size
scales of 10,000 AU at least, the dynamical evolution of starless cores is
probably not controlled by magnetic processes.Comment: 67 pages including 32 figures (highly compressed). Accepted for
publication in the Astronomical Journal. Available with full resolution
(legible) figures at http://www.mrao.cam.ac.uk/%7ejsr/papers/lynds2.ps.g
Complex Structure in Class 0 Protostellar Envelopes III: Velocity Gradients in Non-Axisymmetric Envelopes, Infall or Rotation?
We present an interferometric kinematic study of morphologically complex
protostellar envelopes based on observations of the dense gas tracers N2H+ and
NH3. The strong asymmetric nature of most envelopes in our sample leads us to
question the common interpretation of velocity gradients as rotation, given the
possibility of projection effects in the observed velocities. Several
"idealized" sources with well-ordered velocity fields and envelope structures
are now analyzed in more detail. We compare the interferometric data to
position-velocity diagrams of kinematic models for spherical rotating collapse
and filamentary rotating collapse. For this purpose, we developed a filamentary
parametrization of the rotating collapse model to explore the effects of
geometric projection on the observed velocity structures. We find that most
envelopes in our sample have PV structures that can be reproduced by an
infalling filamentary envelope projected at different angles within the plane
of the sky. The infalling filament produces velocity shifts across the envelope
that can mimic rotation, especially when viewed at single-dish resolutions and
the axisymmetric rotating collapse model does not uniquely describe any
dataset. Furthermore, if the velocities are assumed to reflect rotation, then
the inferred centrifugal radii are quite large in most cases, indicating
significant fragmentation potential or more likely another component to the
line-center velocity. We conclude that ordered velocity gradients cannot be
interpreted as rotation alone when envelopes are non-axisymmetric and that
projected infall velocities likely dominate the velocity field on scales larger
than 1000 AU.Comment: 37 pages, 15 Figures, 2 Tables, Accepted to Ap
S3: Syntax- and semantic-guided repair synthesis via programming by examples
National Science Foundatio
Predicting streamflow with LSTM networks using global datasets
Streamflow predictions remain a challenge for poorly gauged and ungauged catchments. Recent research has shown that deep learning methods based on Long Short-Term Memory (LSTM) cells outperform process-based hydrological models for rainfall-runoff modeling, opening new possibilities for prediction in ungauged basins (PUB). These studies usually feature local datasets for model development, while predictions in ungauged basins at a global scale require training on global datasets. In this study, we develop LSTM models for over 500 catchments from the CAMELS-US data base using global ERA5 meteorological forcing and global catchment characteristics retrieved with the HydroMT tool. Comparison against an LSTM trained with local datasets shows that, while the latter generally yields superior performances due to the higher spatial resolution meteorological forcing (overall median daily NSE 0.54 vs. 0.71), training with ERA5 results in higher NSE in most catchments of Western and North-Western US (median daily NSE of 0.83 vs. 0.78). No significant changes in performance occur when substituting local with global data sources for deriving the catchment characteristics. These results encourage further research to develop LSTM models for worldwide predictions of streamflow in ungauged basins using available global datasets. Promising directions include training the models with streamflow data from different regions of the world and with higher quality meteorological forcing
Complex Structure in Class 0 Protostellar Envelopes II: Kinematic Structure from Single-Dish and Interferometric Molecular Line Mapping
We present a study of dense molecular gas kinematics in seventeen nearby
protostellar systems using single-dish and interferometric molecular line
observations. The non-axisymmetric envelopes around a sample of Class 0/I
protostars were mapped in the N2H+ (J=1-0) tracer with the IRAM 30m, CARMA and
PdBI as well as NH3 (1,1) with the VLA. The molecular line emission is used to
construct line-center velocity and linewidth maps for all sources to examine
the kinematic structure in the envelopes on spatial scales from 0.1 pc to ~1000
AU. The direction of the large-scale velocity gradients from single-dish
mapping is within 45 degrees of normal to the outflow axis in more than half
the sample. Furthermore, the velocity gradients are often quite substantial,
the average being ~2.3 km\s\pc. The interferometric data often reveal
small-scale velocity structure, departing from the more gradual large-scale
velocity gradients. In some cases, this likely indicates accelerating infall
and/or rotational spin-up in the inner envelope; the median velocity gradient
from the interferometric data is ~10.7 km/s/pc. In two systems, we detect
high-velocity HCO+ (J=1-0) emission inside the highest-velocity \nthp\
emission. This enables us to study the infall and rotation close to the disk
and estimate the central object masses. The velocity fields observed on large
and small-scales are more complex than would be expected from rotation alone,
suggesting that complex envelope structure enables other dynamical processes
(i.e. infall) to affect the velocity field.Comment: 85 Pages, 31 Figures, 11 Tables, Accepted to ApJ
Sustainable futures over the next decade are rooted in soil science
Funding information: Dutch Knowledge Base Program; European Commission, Grant/Award Number: NEW 810; Horizon 2020 Framework Programme, Grant/Award Numbers: 774378, 869625; Korea Environmental Industry and Technology Institute, Grant/Award Number: 2019002820004; Natural Environment Research Council, Grant/Award Number: NE/R016429/1; Svenska Forskningsrådet Formas, Grant/Award Number: 2017-00608; UK Research and Innovation, Grant/Award Number: NE/P019455/1Peer reviewedPublisher PD
The potential of C4 grasses for cellulosic biofuel production
With the advent of biorefinery technologies enabling plant biomass to be processed into biofuel, many researchers set out to study and improve candidate biomass crops. Many of these candidates are C4 grasses, characterized by a high productivity and resource use efficiency. In this review the potential of five C4 grasses as lignocellulosic feedstock for biofuel production is discussed. These include three important field crops-maize, sugarcane and sorghum-and two undomesticated perennial energy grasses-miscanthus and switchgrass. Although all these grasses are high yielding, they produce different products. While miscanthus and switchgrass are exploited exclusively for lignocellulosic biomass, maize, sorghum, and sugarcane are dual-purpose crops. It is unlikely that all the prerequisites for the sustainable and economic production of biomass for a global cellulosic biofuel industry will be fulfilled by a single crop. High and stable yields of lignocellulose are required in diverse environments worldwide, to sustain a year-round production of biofuel. A high resource use efficiency is indispensable to allow cultivation with minimal inputs of nutrients and water and the exploitation of marginal soils for biomass production. Finally, the lignocellulose composition of the feedstock should be optimized to allow its efficient conversion into biofuel and other by-products. Breeding for these objectives should encompass diverse crops, to meet the demands of local biorefineries and provide adaptability to different environments. Collectively, these C4 grasses are likely to play a central role in the supply of lignocellulose for the cellulosic ethanol industry. Moreover, as these species are evolutionary closely related, advances in each of these crops will expedite improvements in the other crops. This review aims to provide an overview of their potential, prospects and research needs as lignocellulose feedstocks for the commercial production of biofuel
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