3,751 research outputs found
Tips and Tricks for Visual Question Answering: Learnings from the 2017 Challenge
This paper presents a state-of-the-art model for visual question answering
(VQA), which won the first place in the 2017 VQA Challenge. VQA is a task of
significant importance for research in artificial intelligence, given its
multimodal nature, clear evaluation protocol, and potential real-world
applications. The performance of deep neural networks for VQA is very dependent
on choices of architectures and hyperparameters. To help further research in
the area, we describe in detail our high-performing, though relatively simple
model. Through a massive exploration of architectures and hyperparameters
representing more than 3,000 GPU-hours, we identified tips and tricks that lead
to its success, namely: sigmoid outputs, soft training targets, image features
from bottom-up attention, gated tanh activations, output embeddings initialized
using GloVe and Google Images, large mini-batches, and smart shuffling of
training data. We provide a detailed analysis of their impact on performance to
assist others in making an appropriate selection.Comment: Winner of the 2017 Visual Question Answering (VQA) Challenge at CVP
Functionalized nanopore-embedded electrodes for rapid DNA sequencing
The determination of a patient's DNA sequence can, in principle, reveal an
increased risk to fall ill with particular diseases [1,2] and help to design
"personalized medicine" [3]. Moreover, statistical studies and comparison of
genomes [4] of a large number of individuals are crucial for the analysis of
mutations [5] and hereditary diseases, paving the way to preventive medicine
[6]. DNA sequencing is, however, currently still a vastly time-consuming and
very expensive task [4], consisting of pre-processing steps, the actual
sequencing using the Sanger method, and post-processing in the form of data
analysis [7]. Here we propose a new approach that relies on functionalized
nanopore-embedded electrodes to achieve an unambiguous distinction of the four
nucleic acid bases in the DNA sequencing process. This represents a significant
improvement over previously studied designs [8,9] which cannot reliably
distinguish all four bases of DNA. The transport properties of the setup
investigated by us, employing state-of-the-art density functional theory
together with the non-equilibrium Green's Function method, leads to current
responses that differ by at least one order of magnitude for different bases
and can thus provide a much more robust read-out of the base sequence. The
implementation of our proposed setup could thus lead to a viable protocol for
rapid DNA sequencing with significant consequences for the future of genome
related research in particular and health care in general.Comment: 12 pages, 5 figure
STRINGVACUA: A Mathematica Package for Studying Vacuum Configurations in String Phenomenology
We give a simple tutorial introduction to the Mathematica package
STRINGVACUA, which is designed to find vacua of string-derived or inspired
four-dimensional N=1 supergravities. The package uses powerful
algebro-geometric methods, as implemented in the free computer algebra system
Singular, but requires no knowledge of the mathematics upon which it is based.
A series of easy-to-use Mathematica modules are provided which can be used both
in string theory and in more general applications requiring fast polynomial
computations. The use of these modules is illustrated throughout with simple
examples.Comment: 21 pages, 9 figure
Global stability analysis of an idealized compressor blade row. II. Multiple-blade interactions
A direct-adjoint mean flow global stability investigation of self-excited instabilities in an idealized, two-dimensional compressor blade row at off-design conditions is carried out. In this second part of the paper, the single-passage analysis is extended to multiblade passages by exploiting the properties of block-circulant matrices and Bloch-wave theory. By using this method, analyses for a large number of blade passages become computationally tangible, and the modal and nonmodal single-passage analysis from the first part of the paper can be augmented by considering multiblade effects arising in larger systems. This work shows that multiblade passages introduce additional unstable 10- and five-periodic synchronization structures arising from a tuned optimal phase relationship that is supported by the larger system. Self-excited low-frequency structures, which cannot be represented within a single-passage computation, are also uncovered and analyzed
Linear modal instabilities around post-stall swept finite-aspect ratio wings at low Reynolds numbers
Linear modal instabilities of flow over finite-span untapered wings have been
investigated numerically at Reynolds number 400, at a range of angles of attack
and sweep on two wings having aspect ratios 4 and 8. Base flows have been
generated by direct numerical simulation, marching the unsteady incompressible
three-dimensional Navier-Stokes equations to a steady state, or using selective
frequency damping to obtain stationary linearly unstable flows. Unstable
three-dimensional linear global modes of swept wings have been identified for
the first time using spectral-element time-stepping solvers. The effect of the
wing geometry and flow parameters on these modes has been examined in detail.
An increase of the angle of attack was found to destabilize the flow, while an
increase of the sweep angle had the opposite effect. On unswept wings,
TriGlobal analysis revealed that the most unstable global mode peaks in the
midspan region of the wake; the peak of the mode structure moves towards the
tip as sweep is increased. Data-driven analysis was then employed to study the
effects of wing geometry and flow conditions on the nonlinear wake. On unswept
wings, the dominant mode at low angles of attack is a Kelvin-Helmholtz-like
instability, qualitatively analogous with global modes of infinite-span wings
under same conditions. At higher angles of attack and moderate sweep angles,
the dominant mode is a structure denominated the interaction mode. At high
sweep angles, this mode evolves into elongated streamwise vortices on higher
aspect ratio wings, while on shorter wings it becomes indistinguishable from
tip-vortex instability.Comment: 41 pages, 27 figure
Recycling Strategy for Bioaqueous Phase via Catalytic Wet Air Oxidation to Biobased Acetic Acid Solution
The bioaqueous phase generated during biomass conversion to biofuel and biochemicals, e.g., fast pyrolysis and ex situ catalytic pyrolysis, contains a large number of organics, leading to a high chemical oxygen demand (COD) for its treatment. In this study, we demonstrate its catalytic conversion to bioacetic acid solution and propose a recycling strategy thereof. We found that the diluted bioaqueous phase (e.g., C content 90%) converted to acetic acid with nondetectable impurities in solution. The solution contains 1.3-1.5 wt % acetic acid and can be directly used for demineralization of biomass in the biorefineries. This recycling strategy enhances the sustainability of the biobased economy and sheds light on production of biobased acetic acid, which has been recognized as a smart drop-in chemical
A New Method for Finding Vacua in String Phenomenology
One of the central problems of string-phenomenology is to find stable vacua
in the four dimensional effective theories which result from compactification.
We present an algorithmic method to find all of the vacua of any given
string-phenomenological system in a huge class. In particular, this paper
reviews and then extends hep-th/0606122 to include various non-perturbative
effects. These include gaugino condensation and instantonic contributions to
the superpotential.Comment: 27 pages, 5 .eps figures. V2: Minor corrections, reference adde
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