112 research outputs found
Patch based synthesis for single depth image super-resolution
We present an algorithm to synthetically increase the resolution of a solitary depth image using only a generic database of local patches. Modern range sensors measure depths with non-Gaussian noise and at lower starting resolutions than typical visible-light cameras. While patch based approaches for upsampling intensity images continue to improve, this is the first exploration of patching for depth images. We match against the height field of each low resolution input depth patch, and search our database for a list of appropriate high resolution candidate patches. Selecting the right candidate at each location in the depth image is then posed as a Markov random field labeling problem. Our experiments also show how important further depth-specific processing, such as noise removal and correct patch normalization, dramatically improves our results. Perhaps surprisingly, even better results are achieved on a variety of real test scenes by providing our algorithm with only synthetic training depth data
Explaining Knock-on Effects of Bias Mitigation
In machine learning systems, bias mitigation approaches aim to make outcomes
fairer across privileged and unprivileged groups. Bias mitigation methods work
in different ways and have known "waterfall" effects, e.g., mitigating bias at
one place may manifest bias elsewhere. In this paper, we aim to characterise
impacted cohorts when mitigation interventions are applied. To do so, we treat
intervention effects as a classification task and learn an explainable
meta-classifier to identify cohorts that have altered outcomes. We examine a
range of bias mitigation strategies that work at various stages of the model
life cycle. We empirically demonstrate that our meta-classifier is able to
uncover impacted cohorts. Further, we show that all tested mitigation
strategies negatively impact a non-trivial fraction of cases, i.e., people who
receive unfavourable outcomes solely on account of mitigation efforts. This is
despite improvement in fairness metrics. We use these results as a basis to
argue for more careful audits of static mitigation interventions that go beyond
aggregate metrics.Comment: This paper was accepted at NeurIPS 2023 worksho
An exploratory data analysis of the #Crowdfunding network on Twitter
Together, social media and crowdsourcing can help entrepreneurs to attract external
finance and early-stage customers. This paper investigates the characteristics and discourse of an
issue-centered public on Twitter organized around the hashtag #crowdfunding through the lens of
social network theory. Using a dataset of 2,732,144 tweets published during a calendar year, we use
exploratory data analysis to generate insights and hypotheses on who the users in the #crowdfunding
network are, what they share, and how they are connected to each other. In order to do so, we adopt
a range of descriptive, content, network analytics techniques. The results suggest that platforms,
crowdfunders, and other actors who derive income from the crowdfunding economy play a key
role in creating the network. Furthermore, latent ties (strangers) play a direct role in disseminating
information, investing, and sending signals to platforms that further raises campaign prominence.
We also introduce a new type of social tie, the “computer as a social actor”, previously unaddressed
in entrepreneurial network literature, which play a role in sending signals to both platforms and
networks. Our results suggest that homophily is a key driver for creating network sub-communities
built around specific platforms, project types, domains, or geograph
Reversible Microscale Assembly of Nanoparticles Driven by the Phase Transition of a Thermotropic Liquid Crystal
The arrangement of nanoscale building blocks into patterns with microscale periodicity is challenging to achieve via self-assembly processes. Here, we report on the phase-transition-driven collective assembly of gold nanoparticles in a thermotropic liquid crystal. A temperature-induced transition from the isotropic to the nematic phase under anchoring-driven planar alignment leads to the assembly of individual nanometer-sized particles into arrays of micrometer-sized agglomerates, whose size and characteristic spacing can be tuned by varying the cooling rate. Phase field simulations coupling the conserved and nonconserved order parameters exhibit a similar evolution of the morphology as the experimental observations. This fully reversible process offers control over structural order on the microscopic level and is an interesting model system for the programmable and reconfigurable patterning of nanocomposites with access to micrometer-sized periodicities.</p
Reversible microscale assembly of nanoparticles driven by the phase transition of a thermotropic liquid crystal
The arrangement of nanoscale building blocks into patterns with microscale periodicity is challenging to achieve via self-assembly processes. Here, we report on the phase-transition-driven collective assembly of gold nanoparticles in a thermotropic liquid crystal. A temperature-induced transition from the isotropic to the nematic phase under anchoring-driven planar alignment leads to the assembly of individual nanometer-sized particles into arrays of micrometer-sized agglomerates, whose size and characteristic spacing can be tuned by varying the cooling rate. Phase field simulations coupling the conserved and nonconserved order parameters exhibit a similar evolution of the morphology as the experimental observations. This fully reversible process offers control over structural order on the microscopic level and is an interesting model system for the programmable and reconfigurable patterning of nanocomposites with access to micrometer-sized periodicities
Reversible Microscale Assembly of Nanoparticles Driven by the Phase Transition of a Thermotropic Liquid Crystal
The arrangement of nanoscale building blocks into patterns with microscale periodicity is challenging to achieve via self-assembly processes. Here, we report on the phase-transition-driven collective assembly of gold nanoparticles in a thermotropic liquid crystal. A temperature-induced transition from the isotropic to the nematic phase under anchoring-driven planar alignment leads to the assembly of individual nanometer-sized particles into arrays of micrometer-sized agglomerates, whose size and characteristic spacing can be tuned by varying the cooling rate. Phase field simulations coupling the conserved and nonconserved order parameters exhibit a similar evolution of the morphology as the experimental observations. This fully reversible process offers control over structural order on the microscopic level and is an interesting model system for the programmable and reconfigurable patterning of nanocomposites with access to micrometer-sized periodicities
Visualising Viruses
Viruses pose a challenge to our imaginations. They exert a highly visible influence on the world in which we live, but operate at scales we cannot directly perceive and without a clear separation between their own biology and that of their hosts. Communication about viruses is therefore typically grounded in mental images of the virus particles that transmit viral genomes from one host cell to the next. Virus particles are an important entry point in discussing viruses. The ability to form them is characteristic of all viruses. They can, as the infectious stage of the viral replication cycle, be used to explain many directly observable properties of transmission, infection and immunity. Finally, and importantly, virus particles are often strikingly beautiful and can stimulate further interest in viruses. The structures of some virus particles have been determined experimentally in great detail, but for many important viruses a detailed description of the virus particle is lacking. This can be because they are challenging to describe with a single experimental method, or simply because of a lack of data. In these cases, methods from medical illustration can be applied to produce detailed visualisations of virus particles which integrate information from multiple sources. Here, we demonstrate how this approach was used to visualise the highly variable virus particles of influenza A viruses and, in the early months of the COVID-19 pandemic, the virus particles of the then newly-characterised and poorly described SARS-CoV-2. We show how constructing integrative illustrations of virus particles can challenge our thinking about the biology of viruses as well as providing tools for science communication, and we provide a set of science communication resources to help in visualising two viruses whose effects are extremely apparent to all of us
The formation of disc galaxies in a LCDM universe
We study the formation of disc galaxies in a fully cosmological framework
using adaptive mesh refinement simulations. We perform an extensive parameter
study of the main subgrid processes that control how gas is converted into
stars and the coupled effect of supernovae feedback. We argue that previous
attempts to form disc galaxies have been unsuccessful because of the universal
adoption of strong feedback combined with high star formation efficiencies.
Unless extreme amounts of energy are injected into the interstellar medium
during supernovae events, these star formation parameters result in bulge
dominated S0/Sa galaxies as star formation is too efficient at z~3. We show
that a low efficiency of star-formation more closely models the subparsec
physical processes, especially at high redshift. We highlight the successful
formation of extended disc galaxies with scale lengths r_d=4-5 kpc, flat
rotation curves and bulge to disc ratios of B/D~1/4. Not only do we resolve the
formation of a Milky Way-like spiral galaxy, we also observe the secular
evolution of the disc as it forms a pseudo-bulge. The disc properties agree
well with observations and are compatible with the photometric and baryonic
Tully-Fisher relations, the Kennicutt-Schmidt relation and the observed angular
momentum content of spiral galaxies. We conclude that underlying small-scale
star formation physics plays a larger role than previously considered in
simulations of galaxy formation.Comment: Published in MNRA
A Census of Oxygen in Star-Forming Galaxies: An Empirical Model Linking Metallicities, Star Formation Rates and Outflows
In this contribution we present the first census of oxygen in star-forming
galaxies in the local universe. We examine three samples of galaxies with
metallicities and star formation rates at z = 0.07, 0.8 and 2.26, including the
SDSS and DEEP2 surveys. We infer the total mass of oxygen produced and mass of
oxygen found in the gas-phase from our local SDSS sample. The star formation
history is determined by requiring that galaxies evolve along the relation
between stellar mass and star formation rate observed in our three samples. We
show that the observed relation between stellar mass and star formation rate
for our three samples is consistent with other samples in the literature. The
mass-metallicity relation is well established for our three samples and from
this we empirically determine the chemical evolution of star-forming galaxies.
Thus, we are able to simultaneously constrain the star formation rates and
metallicities of galaxies over cosmic time allowing us to estimate the mass of
oxygen locked up in stars. Combining this work with independent measurements
reported in the literature we conclude that the loss of oxygen from the
interstellar medium of local star-forming galaxies is likely to be a ubiquitous
process with the oxygen mass loss scaling (almost) linearly with stellar mass.
We estimate the total baryonic mass loss and argue that only a small fraction
of the baryons inferred from cosmological observations accrete onto galaxies.Comment: 24 pages, 18 figures. Accepted for publication in Ap
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