169 research outputs found
Micro-opto-mechanical devices and systems using epitaxial lift off
The integration of high quality, single crystal thin film gallium arsenide (GaAs) and indium phosphide (InP) based photonic and electronic materials and devices with host microstructures fabricated from materials such as silicon (Si), glass, and polymers will enable the fabrication of the next generation of micro-opto-mechanical systems (MOMS) and optoelectronic integrated circuits. Thin film semiconductor devices deposited onto arbitrary host substrates and structures create hybrid (more than one material) near-monolithic integrated systems which can be interconnected electrically using standard inexpensive microfabrication techniques such as vacuum metallization and photolithography. These integrated systems take advantage of the optical and electronic properties of compound semiconductor devices while still using host substrate materials such as silicon, polysilicon, glass and polymers in the microstructures. This type of materials optimization for specific tasks creates higher performance systems than those systems which must use trade-offs in device performance to integrate all of the function in a single material system. The low weight of these thin film devices also makes them attractive for integration with micromechanical devices which may have difficulty supporting and translating the full weight of a standard device. These thin film devices and integrated systems will be attractive for applications, however, only when the development of low cost, high yield fabrication and integration techniques makes their use economically feasible. In this paper, we discuss methods for alignment, selective deposition, and interconnection of thin film epitaxial GaAs and InP based devices onto host substrates and host microstructures
Astrometric orbits of SB9 stars
Hipparcos Intermediate Astrometric Data (IAD) have been used to derive
astrometric orbital elements for spectroscopic binaries from the newly released
Ninth Catalogue of Spectroscopic Binary Orbits (SB9). Among the 1374 binaries
from SB9 which have an HIP entry, 282 have detectable orbital astrometric
motion (at the 5% significance level). Among those, only 70 have astrometric
orbital elements that are reliably determined (according to specific
statistical tests discussed in the paper), and for the first time for 20
systems, representing a 10% increase relative to the 235 DMSA/O systems already
present in the Hipparcos Double and Multiple Systems Annex.
The detection of the astrometric orbital motion when the Hipparcos IAD are
supplemented by the spectroscopic orbital elements is close to 100% for
binaries with only one visible component, provided that the period is in the 50
- 1000 d range and the parallax is larger than 5 mas. This result is an
interesting testbed to guide the choice of algorithms and statistical tests to
be used in the search for astrometric binaries during the forthcoming ESA Gaia
mission.
Finally, orbital inclinations provided by the present analysis have been used
to derive several astrophysical quantities. For instance, 29 among the 70
systems with reliable astrometric orbital elements involve main sequence stars
for which the companion mass could be derived. Some interesting conclusions may
be drawn from this new set of stellar masses, like the enigmatic nature of the
companion to the Hyades F dwarf HIP 20935. This system has a mass ratio of 0.98
but the companion remains elusive.Comment: Astronomy & Astrophysics, in press (16 pages, 12 figures); also
available at http://www.astro.ulb.ac.be/Html/ps.html#Astrometr
An ant colony-based semi-supervised approach for learning classification rules
Semi-supervised learning methods create models from a few labeled instances and a great number of unlabeled instances. They appear as a good option in scenarios where there is a lot of unlabeled data and the process of labeling instances is expensive, such as those where most Web applications stand. This paper proposes a semi-supervised self-training algorithm called Ant-Labeler. Self-training algorithms take advantage of supervised learning algorithms to iteratively learn a model from the labeled instances and then use this model to classify unlabeled instances. The instances that receive labels with high confidence are moved from the unlabeled to the labeled set, and this process is repeated until a stopping criteria is met, such as labeling all unlabeled instances. Ant-Labeler uses an ACO algorithm as the supervised learning method in the self-training procedure to generate interpretable rule-based models—used as an ensemble to ensure accurate predictions. The pheromone matrix is reused across different executions of the ACO algorithm to avoid rebuilding the models from scratch every time the labeled set is updated. Results showed that the proposed algorithm obtains better predictive accuracy than three state-of-the-art algorithms in roughly half of the datasets on which it was tested, and the smaller the number of labeled instances, the better the Ant-Labeler performance
Time resolved spectroscopy of BD+46 442: gas streams and jet creation in a newly discovered evolved binary with a disk
Previous studies have shown that many post-AGB stars with dusty disks are
associated with single-lined binary stars. To verify the binarity hypothesis on
a larger sample, we started a high-resolution spectral monitoring of about 40
field giants, whose binarity was suspected based on either a light curve, an
infrared excess, or a peculiar chemical composition. Here we report on the
discovery of the periodic RV variations in BD+46 442, a high-latitude F giant
with a disk. We interpret the variations due to the motion around a faint
companion, and deduce the following orbital parameters: Porb = 140.77 d, e =
0.083, asini=0.31 AU. We find it to be a moderately metal-poor star
([M/H]=-0.7) without a strong depletion pattern in the photospheric abundances.
Interestingly, many lines show periodic changes with the orbital phase: Halpha
switches between a double-peak emission and a PCyg-like profiles, while strong
metal lines appear split during the maximum redshift. Similar effects are
likely visible in the spectra of other post-AGB binaries, but their regularity
is not always realized due to sporadic observations. We propose that these
features result from an ongoing mass transfer from the evolved giant to the
companion. In particular, the blue-shifted absorption in Halpha, which occurs
only at superior conjunction, may result from a jet originating in the
accretion disk around the companion and seen in absorption towards the luminous
primary.Comment: 16 pages, accepted in A&
Nitrogen-limited mangrove ecosystems conserve N through dissimilatory nitrate reduction to ammonium
Earlier observations in mangrove sediments of Goa, India have shown denitrification to be a major pathway for N loss1. However, percentage of total nitrate transformed through complete denitrification accounted for <0–72% of the pore water nitrate reduced. Here, we show that up to 99% of nitrate removal in mangrove sediments is routed through dissimilatory nitrate reduction to ammonium (DNRA). The DNRA process was 2x higher at the relatively pristine site Tuvem compared to the anthropogenically-influenced Divar mangrove ecosystem. In systems receiving low extraneous nutrient inputs, this mechanism effectively conserves and re-circulates N minimizing nutrient loss that would otherwise occur through denitrification. In a global context, the occurrence of DNRA in mangroves has important implications for maintaining N levels and sustaining ecosystem productivity. For the first time, this study also highlights the significance of DNRA in buffering the climate by modulating the production of the greenhouse gas nitrous oxide
The Effect of Learning to Drum on Behaviour and Brain Function in Autistic Adolescents
There is an acknowledged need for improved service provision in the context of autism spectrum disorders. Previous studies have demonstrated the positive role drum training can play in improving behavioral outcomes for children and adolescents with emotional and behavioral difficulties. However, to date, none of these studies has explored how these behavioral changes translate at the neural level. Our study provides strong evidence that drumming not only reduces hyperactivity and inattention in autistic adolescents but also strengthens functional connectivity in brain regions responsible for inhibitory control and action outcome monitoring
Shock compression experiments using the DiPOLE 100-X laser on the high energy density instrument at the European x-ray free electron laser: quantitative structural analysis of liquid Sn
X-ray free electron laser (XFEL) sources coupled to high-power laser systems offer an avenue to study the structural dynamics of materials at extreme pressures and temperatures. The recent commissioning of the DiPOLE 100-X laser on the high energy density (HED) instrument at the European XFEL represents the state-of-the-art in combining x-ray diffraction with laser compression, allowing for compressed materials to be probed in unprecedented detail. Here, we report quantitative structural measurements of molten Sn compressed to 85(5) GPa and ∼ 3500 K. The capabilities of the HED instrument enable liquid density measurements with an uncertainty of ∼ 1 % at conditions which are extremely challenging to reach via static compression methods. We discuss best practices for conducting liquid diffraction dynamic compression experiments and the necessary intensity corrections which allow for accurate quantitative analysis. We also provide a polyimide ablation pressure vs input laser energy for the DiPOLE 100-X drive laser which will serve future users of the HED instrument
Enrichment and characterization of ammonia-oxidizing archaea from the open ocean : phylogeny, physiology and stable isotope fractionation
Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in The ISME Journal 5 (2011): 1796–1808, doi:10.1038/ismej.2011.58.Archaeal genes for ammonia oxidation are widespread in the marine environment, but
direct physiological evidence for ammonia oxidation by marine archaea is limited. We
report the enrichment and characterization of three strains of pelagic ammonia-oxidizing
archaea (AOA) from the north Pacific Ocean that have been maintained in laboratory
culture for over three years. Phylogenetic analyses indicate the three strains belong to a
previously identified clade of water column-associated AOA and possess 16S rRNA
genes and ammonia monooxygenase subunit a (amoA) genes highly similar (98-99%
identity) to those recovered in DNA and cDNA clone libraries from the open ocean. The
strains grow in natural seawater-based liquid medium while stoichiometrically converting
ammonium (NH4
+) to nitrite (NO2
-). Ammonia oxidation by the enrichments is only
partially inhibited by allylthiourea at concentrations known to inhibit cultivated
ammonia-oxidizing bacteria. The three strains were used to determine the nitrogen stable
isotope effect (15εNH3) during archaeal ammonia oxidation, an important parameter for
interpreting stable isotope ratios in the environment. Archaeal 15εNH3 ranged from 13-
41‰, within the range of that previously reported for ammonia-oxidizing bacteria.
Despite low amino acid identity between the archaeal and bacterial Amo proteins, their
functional diversity as captured by 15εNH3 is similar.This work was supported by a Woods Hole Oceanographic Institution (WHOI)
Postdoctoral Scholar fellowship to AES and the WHOI Ocean Life Institute
Variability and magnitude of brain glutamate levels in schizophrenia: a meta and mega-analysis
Glutamatergic dysfunction is implicated in schizophrenia pathoaetiology, but this may vary in extent between patients. It is unclear whether inter-individual variability in glutamate is greater in schizophrenia than the general population. We conducted meta-analyses to assess (1) variability of glutamate measures in patients relative to controls (log coefficient of variation ratio: CVR); (2) standardised mean differences (SMD) using Hedges g; (3) modal distribution of individual-level glutamate data (Hartigan’s unimodality dip test). MEDLINE and EMBASE databases were searched from inception to September 2022 for proton magnetic resonance spectroscopy (1H-MRS) studies reporting glutamate, glutamine or Glx in schizophrenia. 123 studies reporting on 8256 patients and 7532 controls were included. Compared with controls, patients demonstrated greater variability in glutamatergic metabolites in the medial frontal cortex (MFC, glutamate: CVR = 0.15, p < 0.001; glutamine: CVR = 0.15, p = 0.003; Glx: CVR = 0.11, p = 0.002), dorsolateral prefrontal cortex (glutamine: CVR = 0.14, p = 0.05; Glx: CVR = 0.25, p < 0.001) and thalamus (glutamate: CVR = 0.16, p = 0.008; Glx: CVR = 0.19, p = 0.008). Studies in younger, more symptomatic patients were associated with greater variability in the basal ganglia (BG glutamate with age: z = −0.03, p = 0.003, symptoms: z = 0.007, p = 0.02) and temporal lobe (glutamate with age: z = −0.03, p = 0.02), while studies with older, more symptomatic patients associated with greater variability in MFC (glutamate with age: z = 0.01, p = 0.02, glutamine with symptoms: z = 0.01, p = 0.02). For individual patient data, most studies showed a unimodal distribution of glutamatergic metabolites. Meta-analysis of mean differences found lower MFC glutamate (g = −0.15, p = 0.03), higher thalamic glutamine (g = 0.53, p < 0.001) and higher BG Glx in patients relative to controls (g = 0.28, p < 0.001). Proportion of males was negatively associated with MFC glutamate (z = −0.02, p < 0.001) and frontal white matter Glx (z = −0.03, p = 0.02) in patients relative to controls. Patient PANSS total score was positively associated with glutamate SMD in BG (z = 0.01, p = 0.01) and temporal lobe (z = 0.05, p = 0.008). Further research into the mechanisms underlying greater glutamatergic metabolite variability in schizophrenia and their clinical consequences may inform the identification of patient subgroups for future treatment strategies
- …