2,061 research outputs found
Recent developments of MCViNE and its applications at SNS
MCViNE is an open source, object-oriented Monte Carlo neutron ray-tracing simulation software package. Its design allows for flexible, hierarchical representations of sophisticated instrument components such as detector systems, and samples with a variety of shapes and scattering kernels. Recently this flexible design has enabled several applications of MCViNE simulations at the Spallation Neutron Source (SNS) at Oak Ridge National Lab, including assisting design of neutron instruments at the second target station and design of novel sample environments, as well as studying effects of instrument resolution and multiple scattering. Here we provide an overview of the recent developments and new features of MCViNE since its initial introduction (Jiao et al 2016 Nucl. Instrum. Methods Phys. Res., Sect. A 810, 86–99), and some example applications
Microsatellite development for the genus Guibourtia (Fabaceae, Caesalpinioideae) reveals diploid and polyploid species
Premise of the study: Nuclear microsatellites (nSSRs) were designed for Guibourtia tessmannii (Fabaceae, Caesalpinioideae), a highly exploited African timber tree, to study population genetic structure and gene flow.
Methods and Results: We developed 16 polymorphic nSSRs from a genomic library tested in three populations of G. tessmannii and two populations of G. coleosperma. These nSSRs display three to 14 alleles per locus (mean 8.94) in G. tessmannii. Cross-amplification tests in nine congeneric species demonstrated that the genus Guibourtia contains diploid and polyploid species. Flow cytometry results combined with nSSR profiles suggest that G. tessmannii is octoploid.
Conclusions: nSSRs revealed that African Guibourtia species include both diploid and polyploid species. These markers will provide information on the mating system, patterns of gene flow, and genetic structure of African Guibourtia species
Intelligent chilled mirror humidity sensor
A new, intelligent, chilled mirror humidity instrument has been designed
for use on buoys and ships. The design goal is to make high quality dew point
temperature measurements for a period of up to one year from an unattended
platform, while consuming as little power as possible. Nominal system accuracy
is 0.3°C, and a measure of data quality is provided to indicate possible drift in
calibration. Energy consumption is typically 800 Joules per measurement; standby
power consumption is 0.05 watts. Control of the instrument is managed by an onboard
central processing unit which is programmable in BASIC, and communication
to an external data logger is provided through an RS232 compatible interface. This
report describes the preliminary sensor tests that led to this new design and provides
the complete technical description required for fabrication.Funding was provided by the Office of Naval Research
under contract Number N00014-84-C-0134,
and the National Science Foundation
through grant Number OCE87- 09614
Multilevel ensemble transform particle filtering
This paper extends the multilevel Monte Carlo variance reduction technique to nonlinear filtering. In particular, multilevel Monte Carlo is applied to a certain variant of the particle filter, the ensemble transform particle filter (EPTF). A key aspect is the use of optimal transport methods to re-establish correlation between coarse and fine ensembles after resampling; this controls the variance of the estimator. Numerical examples present a proof of concept of the effectiveness of the proposed method, demonstrating significant computational cost reductions (relative to the single-level ETPF counterpart) in the propagation of ensembles
What can we learn about protoplanetary disks from analysis of mid-infrared carbonaceous dust emission?
In this Paper we analyze the mid-infrared (mid-IR) emission of very small
dust particles in a sample of 12 protoplanetary disks to see how they are
connected to interstellar dust particles and to investigate the possibility
that their emission can be used as a probe of the physical conditions and
evolution of the disk. We define a basis made of three mid-IR template spectra
PAH, PAH and VSGs that were derived from the analysis of reflection
nebulae, and an additional PAH spectrum that was introduced by Joblin et
al. (2008) for the analysis of the spectra of planetary nebulae. From the
optimization of the fit of 12 star+disk spectra, using a linear combination of
the 4 template spectra, we found that an additional small grain component with
a broad feature at 8.3 m is needed. We find that the fraction of VSG
emission in disks decreases with increasing stellar temperature. VSGs appear to
be destroyed by UV photons at the surface of disks, thus releasing free PAH
molecules, which are eventually ionized as it is observed in photodissociation
regions. On the opposite, we observe that the fraction of PAH increases
with increasing star temperature except in the case of B stars where they are
absent. We argue that this is compatible with the identification of PAH as
large ionized PAHs, most likely emitting in regions of the disk that are close
to the star. Finally, we provide a UV-dependant scheme to explain the evolution
of PAHs and VSGs in protoplanetary disks. We show that A stars modify the size
spectrum of PAHs and VSGs in favor of large PAHs while B stars destroy even the
largest PAHs up to large radii in the disk. These results allow us to put new
constrains on the properties of two sources: IRS 48 and "Gomez's Hamburger"
which are poorly characterized.Comment: Accepted for publication in A&
On Reasoning on Time and Location on the Web
Reasoning on time and location is receiving increasing attention on the Web due to emerging fields like Web adaptation, mobile computing, and the Semantic Web. Web applications in these fields often refer to rather complex temporal, calendric, and location information. Unfortunately, today’s Web languages and formalisms have merely primitive temporal and location data types and temporal and location reasoning capabilities – if any. This article reports on work in progress aiming at integrating temporal and locational reasoning into XML query and transformation operations. We analyze the problem and propose a concrete architecture. A prototype of the temporal reasoner, the WebCal system has already been realized
The nearby eclipsing stellar system delta Velorum - I. Origin of the infrared excess from VISIR and NACO imaging
- Context: The triple stellar system delta Vel system presents a significant
infrared excess, whose origin is still being debated. A large infrared bow
shock has been discovered using Spitzer/MIPS observations. Although it appears
as a significant contributor to the measured IR excess, the possibility exists
that a circumstellar IR excess is present around the stars of the system. -
Aims: The objective of the present VISIR and NACO observations is to identify
whether one of the stars of the delta Vel system presents a circumstellar
photometric excess in the thermal IR domain and to quantify it. - Methods: We
observed delta Vel using the imaging modes of the ESO/VLT instruments VISIR (in
BURST mode) and NACO to resolve the A-B system (0.6" separation) and obtain the
photometry of each star. We also obtained one NACO photometry epoch precisely
at the primary (annular) eclipse of delta Vel Aa by Ab. - Results: Our
photometric measurements with NACO (2.17 mic), complemented by the existing
visible photometry allowed us to reconstruct the spectral energy distribution
of the three stars. We then compared the VISIR photometry (8.6-12.8 mic) to the
expected photospheric emission from the three stars at the corresponding
wavelengths. - Conclusions: We can exclude the presence of a circumstellar
thermal infrared excess around delta Vel A or B down to a few percent level.
This supports the conclusions of Gaspar et al. (2008) that the IR excess of
delta Vel has an interstellar origin, although a cold circumstellar disk could
still be present. In addition, we derive the spectral types of the three stars
Aa, Ab, and B (respectively A2IV, A4V and F8V), and we estimate the age of the
system around 400-500 Myr.Comment: 8 pages, 9 figures, A&A, in pres
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