849 research outputs found
On Derandomizing Local Distributed Algorithms
The gap between the known randomized and deterministic local distributed
algorithms underlies arguably the most fundamental and central open question in
distributed graph algorithms. In this paper, we develop a generic and clean
recipe for derandomizing LOCAL algorithms. We also exhibit how this simple
recipe leads to significant improvements on a number of problem. Two main
results are:
- An improved distributed hypergraph maximal matching algorithm, improving on
Fischer, Ghaffari, and Kuhn [FOCS'17], and giving improved algorithms for
edge-coloring, maximum matching approximation, and low out-degree edge
orientation. The first gives an improved algorithm for Open Problem 11.4 of the
book of Barenboim and Elkin, and the last gives the first positive resolution
of their Open Problem 11.10.
- An improved distributed algorithm for the Lov\'{a}sz Local Lemma, which
gets closer to a conjecture of Chang and Pettie [FOCS'17], and moreover leads
to improved distributed algorithms for problems such as defective coloring and
-SAT.Comment: 37 page
Towards a continuous modeling of natural language domains
Humans continuously adapt their style and language to a variety of domains.
However, a reliable definition of `domain' has eluded researchers thus far.
Additionally, the notion of discrete domains stands in contrast to the
multiplicity of heterogeneous domains that humans navigate, many of which
overlap. In order to better understand the change and variation of human
language, we draw on research in domain adaptation and extend the notion of
discrete domains to the continuous spectrum. We propose representation
learning-based models that can adapt to continuous domains and detail how these
can be used to investigate variation in language. To this end, we propose to
use dialogue modeling as a test bed due to its proximity to language modeling
and its social component.Comment: 5 pages, 3 figures, published in Uphill Battles in Language
Processing workshop, EMNLP 201
Barrow holographic dark energy in the Brans-Dicke cosmology
We construct a holographic model for dark energy in the Brans-Dicke cosmology
by using the holographic principle considering the Barrow entropy instead of
the standard Bekenstein-Hawking one. The former arises from the effort to
account for quantum-gravitational effects in black-hole physics and, according
to the gravity-thermodynamic conjecture, in the cosmological framework. In
order to explore the cosmological consequences of our model, we consider the
Hubble horizon as the IR cutoff. We investigate both the non-interacting and
interacting cases with the sign-changeable and linear interactions, showing
that they can explain the present accelerated phase of the Universe expansion,
in contrast to the standard Holographic Dark Energy model. We then perform the
classical stability analysis using the squared sound speed. We find that,
whilst the non-interacting model is unstable against the small perturbations,
the sign-changeable interacting one can be stable only for suitable values of
the model parameters. On the other hand, the linear interacting model always
predicts a stable Universe. The consistency of our model with cosmological
observations is discussed.Comment: 9 pages, 15 figure
Warped Gaussian Processes Occupancy Mapping with Uncertain Inputs
© 2017 IEEE. In this paper, we study extensions to the Gaussian processes (GPs) continuous occupancy mapping problem. There are two classes of occupancy mapping problems that we particularly investigate. The first problem is related to mapping under pose uncertainty and how to propagate pose estimation uncertainty into the map inference. We develop expected kernel and expected submap notions to deal with uncertain inputs. In the second problem, we account for the complication of the robot's perception noise using warped Gaussian processes (WGPs). This approach allows for non-Gaussian noise in the observation space and captures the possible nonlinearity in that space better than standard GPs. The developed techniques can be applied separately or concurrently to a standard GP occupancy mapping problem. According to our experimental results, although taking into account pose uncertainty leads, as expected, to more uncertain maps, by modeling the nonlinearities present in the observation space WGPs improve the map quality
Mass Transport of Lignin in Confined Pores
A crucial step in the chemical delignification of wood is the transport of lignin fragments into free liquor; this step is believed to be the rate-limiting step. This study has investigated the diffusion of kraft lignin molecules through model cellulose membranes of various pore sizes (1-200 nm) by diffusion cells, where the lignin molecules diffuse from donor to acceptor cells through a membrane, where diffusion rate increases by pore size. UV-vis spectra of the donor solutions showed greater absorbance at higher wavelengths (similar to 450 nm), which was probably induced by scattering due to presence of large molecules/clusters, while acceptor samples passed through small pore membranes did not. The UV-vis spectra of acceptor solutions show a characteristic peak at around 350 nm, which corresponds to ionized conjugated molecules: indicating that a chemical fractionation has occurred. Size exclusion chromatography (SEC) showed a difference in the molecular weight (M-w) distribution between lignin from the donor and acceptor chambers. The results show that small pore sizes enable the diffusion of small individual molecules and hinder the transport of large lignin molecules or possible lignin clusters. This study provides more detail in understanding the mass transfer events of pulping processes
Exploration in Information Distribution Maps
In this paper, a novel solution for autonomous robotic exploration is proposed. The distribution of information in an unknown environment is modeled as an unsteady diffusion process, which can be an appropriate mathematical formulation and analogy for expanding, time-varying, and dynamic environments. This information distribution map is the solution of the diffusion process partial differential equation, and is regressed from sensor data as a Gaussian Process. Optimization of the process parameters leads to an optimal frontier map which describes regions of interest for further exploration. Since the presented approach considers a continuous model of the environment, it can be used to plan smooth exploration paths exploiting the structural dependencies of the environment whilst handling sparse sensors measurements. The performance of the proposed approach is evaluated through simulation results in the well-known Freiburg and Cave maps
Effect of alkalinity on the diffusion of solvent-fractionated lignin through cellulose membranes
Mass transport of liberated lignin fragments from pits and fiber walls into black liquor is considered a determining step in the delignification process. However, our current understanding of the diffusion of lignin through cellulose and the influential parameter on this process is very limited. A comprehensive and detailed study of lignin mass transport through cellulosic materials is, therefore, of great importance. In this study, diffusion cell methodology is implemented to systematically investigate the transport of fractionated kraft lignin molecules through model cellulose membranes. Pulping is a complex process and lignin is very heterogenous material therefore to perform a more detailed study on lignin diffusion, we included an additional solvent fractionation step. One of the benefits of this method is that the setup can be adjusted to various experimental conditions allowing the complex chemical reactions occurring during pulping, which would affect the mass transfer of lignin, to be avoided. Here, the effects of the alkalinity of the aqueous solution and molecular weight of the kraft lignin molecules on their diffusion were investigated. Additionally,\ua0NMR spectroscopy, size exclusion chromatography, and UV/Vis spectroscopy were used to characterize the starting material and the molecules that passed through the membrane. Lignin molecules detected in the acceptor chamber of the diffusion cells had lower molecular weights, indicating a size fractionation between the donor and acceptor chamber. UV/Vis showed higher concentrations of ionized conjugated kraft lignin molecules in the acceptor chamber, which is a sign of chemical fractionation. This study suggests that the diffusion of lignin through small cellulose pores can be enhanced by decreasing the average molecular weight of the diffusing kraft lignin molecules and increasing alkalinity
A Directional Crack Damage Memory Effect in Sandstone Under True Triaxial Loading
We thank J.G. Van Munster for providing access to the true triaxial apparatus at KSEPL and for technical support during the experimental program. This work was partly funded by NERC awards NE/N002938/1, NE/N003063/1, and by a NERC Doctoral Studentship, which we gratefully acknowledge. Supporting data are included in an SI file; any additional data may be obtained from JB (email: [email protected]).Peer reviewedPublisher PD
A continuous source of translationally cold dipolar molecules
The Stark interaction of polar molecules with an inhomogeneous electric field
is exploited to select slow molecules from a room-temperature reservoir and
guide them into an ultrahigh vacuum chamber. A linear electrostatic quadrupole
with a curved section selects molecules with small transverse and longitudinal
velocities. The source is tested with formaldehyde (H2CO) and deuterated
ammonia (ND3). With H2CO a continuous flux is measured of approximately 10^9/s
and a longitudinal temperature of a few K. The data are compared with the
result of a Monte Carlo simulation.Comment: 4 pages, 4 figures v2: small changes in the abstract, text and
references. Figures 1 & 2 regenerated to prevent errors in the pd
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