2,437 research outputs found
A phase-space approach to directional switching in semiconductor ring lasers
We show that a topological investigation of the phase space of a
Semiconductor Ring Laser can be used to devise switching schemes which are
alternative to optical pulse injection of counter-propagating light. To provide
physical insight in these switching mechanisms, a full bifurcation analysis and
an investigation of the topology is performed on a two-dimensional asymptotic
model. Numerical simulations confirm the topological predictions.Comment: 9 pages, 7 figure
Excitability in semiconductor microring lasers: Experimental and theoretical pulse characterization
We characterize the operation of semiconductor microring lasers in an
excitable regime. Our experiments reveal a statistical distribution of the
characteristics of noise-triggered optical pulses that is not observed in other
excitable systems. In particular, an inverse correlation exists between the
pulse amplitude and duration. Numerical simulations and an interpretation in an
asymptotic phase space confirm and explain these experimentally observed pulse
characteristics.Comment: 9 pages, 10 figure
Exploring multi-stability in semiconductor ring lasers: theory and experiment
We report the first experimental observation of multi-stable states in a
single-longitudinal mode semiconductor ring laser. We show how the operation of
the device can be steered to either monostable, bistable or multi-stable
dynamical regimes in a controlled way. We observe that the dynamical regimes
are organized in well reproducible sequences that match the bifurcation
diagrams of a two-dimensional model. By analyzing the phase space in this
model, we predict how the stochastic transitions between multi-stable states
take place and confirm it experimentally.Comment: 4 pages, 5 figure
Sulphur-bearing molecules in AGB stars I: The occurrence of hydrogen sulfide
Through a survey of (sub-)millimetre emission lines of various
sulphur-bearing molecules, we aim to determine which molecules are the primary
carriers of sulphur in different types of AGB stars. In this paper, the first
in a series, we investigate the occurrence of HS in AGB circumstellar
envelopes and determine its abundance, where possible. We have surveyed 20 AGB
stars with a range of mass-loss rates and of different chemical types using the
APEX telescope to search for rotational transition lines of five key
sulphur-bearing molecules: CS, SiS, SO, SO and HS. Here we present our
results for HS, including detections, non-detections and detailed radiative
transfer modelling of the detected lines. We compare results based on different
descriptions of the molecular excitation of HS and different abundance
distributions, including those derived from chemical modelling results. We
detected HS towards five AGB stars, all of which have high mass-loss rates
of yr and are oxygen-rich. HS
was not detected towards the carbon or S-type stars that fall in a similar
mass-loss range. For the stars in our sample with detections, we find peak
o-HS abundances relative to H between and . Overall, we conclude that HS can play a significant role in
oxygen-rich AGB stars with higher mass-loss rates, but is unlikely to play a
key role in stars of other chemical types or the lower mass-loss rate
oxygen-rich stars. For two sources, V1300 Aql and GX Mon, HS is most likely
the dominant sulphur-bearing molecule in the circumstellar envelope.Comment: 14 pages, 7 figures, accepted in A&
Disentangling physics and chemistry in AGB outflows: revealing degeneracies when adding complexity
Observations of the outflows of asymptotic giant branch (AGB) stars continue
to reveal their chemical and dynamical complexity. Spherical asymmetries, such
as spirals and disks, are prevalent and thought to be caused by binary
interaction with a (sub)stellar companion. Furthermore, high density outflows
show evidence of dust-gas interactions. The classical chemical model of these
outflows - a gas-phase only, spherically symmetric chemical kinetics model - is
hence not appropriate for a majority of observed outflows. We have included
several physical and chemical advancements step-by-step: a porous density
distribution, dust-gas chemistry, and internal UV photons originating from a
close-by stellar companion. Now, we combine these layers of complexity into the
most chemically and physically advanced chemical kinetics model of AGB outflows
to date. By varying over all model parameters, we obtain a holistic view of the
outflow's composition and how it (inter)depends on the different complexities.
A stellar companion has the largest influence, especially when combined with a
porous outflow. We compile sets of gas-phase molecules that trace the
importance of dust-gas chemistry and allow us to infer the presence of a
companion and porosity of the outflow. This shows that our new chemical model
can be used to infer physical and chemical properties of specific outflows, as
long as a suitable range of molecules is observed.Comment: Faraday Discussions 2023, accepted manuscript. 15 pages, 7 figures, 4
tables. Supplementary information can be found at
https://pubs.rsc.org/en/content/articlelanding/2023/fd/d3fd00039
Impact of nonlocal interactions in dissipative systems: towards minimal-sized localized structures
In order to investigate the size limit on spatial localized structures in a
nonlinear system, we explore the impact of linear nonlocality on their domains
of existence and stability. Our system of choice is an optical microresonator
containing an additional metamaterial layer in the cavity, allowing the
nonlocal response of the material to become the dominating spatial process. In
that case, our bifurcation analysis shows that this nonlocality imposes a new
limit on the width of localized structures going beyond the traditional
diffraction limit.Comment: 4 pages, 4 figure
genomepy: genes and genomes at your fingertips
Analyzing a functional genomics experiment, such as ATAC-, ChIP- or
RNA-sequencing, requires reference data including a genome assembly and gene
annotation. These resources can generally be retrieved from different
organizations and in different versions. Most bioinformatic workflows require
the user to supply this genomic data manually, which can be a tedious and
error-prone process.
Here we present genomepy, which can search, download, and preprocess the
right genomic data for your analysis. Genomepy can search genomic data on NCBI,
Ensembl, UCSC and GENCODE, and compare available gene annotations to enable an
informed decision. The selected genome and gene annotation can be downloaded
and preprocessed with sensible, yet controllable, defaults. Additional
supporting data can be automatically generated or downloaded, such as aligner
indexes, genome metadata and blacklists.
Genomepy is freely available at https://github.com/vanheeringen-lab/genomepy
under the MIT license and can be installed through pip or bioconda
Dawn of the red and dead : stellar kinematics of massive quiescent galaxies out to z = 2
The first massive elliptical galaxies were already in place when the Universe was only 3 billions years old. Surprisingly, they are more compact in comparison to their present-day counterparts. In this thesis these recent findings are assessed by measuring the stellar kinematics of massive z=2 galaxies from spectra obtained with X-Shooter on the Very Large Telescope. This thesis work shows that high-redshift galaxies are truly very massive and structurally very different from present-day galaxies, yet they follow the same scaling relations.Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) en het Leids Kerkhoven Bosscha fonds (LKBF).UBL - phd migration 201
Hydrophobic drug/toxin binding sites in voltage-dependent K+ and Na+ channels
In the Na(v)channel family the lipophilic drugs/toxins binding sites and the presence of fenestrations in the channel pore wall are well defined and categorized. No such classification exists in the much larger K(v)channel family, although certain lipophilic compounds seem to deviate from binding to well-known hydrophilic binding sites. By mapping different compound binding sites onto 3D structures of Kv channels, there appear to be three distinct lipid-exposed binding sites preserved in K(v)channels: the front and back side of the pore domain, and S2-S3/S3-S4 clefts. One or a combination of these sites is most likely the orthologous equivalent of neurotoxin site 5 in Na(v)channels. This review describes the different lipophilic binding sites and location of pore wall fenestrations within the K(v)channel family and compares it to the knowledge of Na(v)channels
Fast human activity recognition in lifelogging
This paper addresses the problem of fast Human Activity Recognition (HAR) in visual lifelogging. We identify the importance of visual features related to HAR and we specifically evaluate the HAR discrimination potential of Colour Histograms and Histogram of Oriented Gradients. In our evaluation we show that colour can be a low-cost and effective means of low-cost HAR when performing single-user classification. It is also noted that, while much more efficient, global image descriptors perform as well or better than local descriptors in our HAR experiments. We believe that both of these findings are due to the fact that a user’s lifelog is rich in reoccurring scenes and environments
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