6,127 research outputs found
Best-first Enumeration Based on Bounding Conflicts, and its Application to Large-scale Hybrid Estimation
With the rise of autonomous systems, there is a need for them to have high levels of robustness and safety. This robustness can be achieved through systems that are self-repairing. Underlying this is the ability to diagnose subtle failures. Likewise, online planners can generate novel responses to exceptional situations. These planners require an accurate estimate of state. Estimation methods based on hybrid discrete/continuous state models have emerged as a method of computing precise state estimates, which can be employed for either diagnosis or planning in hybrid domains. However, existing methods have difficulty scaling to systems with more than a handful of components. Discrete state estimation capabilities can scale to this level by combining best-first enumeration and conflict-directed search. Best-first methods have been developed for hybrid estimation, but the creation of conflict-directed methods has previously been elusive. While conflicts are used to learn from constraint violation, probabilistic hybrid estimation is relatively unconstrained. In this paper we present an approach to hybrid estimation that unifies best-first enumeration and conflict-directed search through the concept of "bounding" conflicts, an extension of conflicts that represent tighter bounds on the cost of regions of the search space. This paper presents a general best-first search and enumeration algorithm based on bounding conflicts (A*BC) and a hybrid estimation method based on this enumeration algorithm. Experiments show that an A*BC powered state estimator produces estimates faster than the current state of the art, particularly on large systems
Analysis of the 2007/8 Defra Farm Business Survey Energy Module
Key points This study has delivered an invaluable baseline estimate of energy
use and greenhouse gas (GHG) emissions on commercial farms in England. Energy
use and GHG emissions associated with particular commodities were quantified and
results broadly agreed with those derived by Life Cycle Assessment, but with
much scatter in the environmental performance of farms.Direct energy use on
farms was generally less that indirect (embedded) energy use, except for
horticulture, which is dominated by heating fuel use. In contrast, most GHG
emissions are incurred on farms, rather than as embedded emissions.Scatter in
both environmental and economic performance underlies the somewhat disappointing
finding of no clear positive link between farm financial performance and energy
use or GHG emissions. However, the mere existence of these ranges shows that
there is scope for improvement in both financial and environmental performance
and that there is no apparent barrier for both to be achievable in harmony. The
recording of such farm-level energy data is essential for the future, as it
should enable improvements to be made in efficiency of energy use. The improved
UK agricultural GHG inventory will depend on high quality energy data on
agricultural activities. This study will be invaluable in identifying the level
of detail needed. Future data requirements include: contractor work rates and
fuel use per unit area and per unit time, fertiliser and pesticide use by brand
name, enhanced output data, especially animal live weights, and horticultural
produce recorded by weight rather than by value
Tailoring of arteriovenous graft‑to‑vein anastomosis angle to attenuate pathological flow fields
Abstract Arteriovenous grafts are routinely placed to facilitate hemodialysis in patients with end stage renal disease. These grafts are conduits between higher pressure arteries and lower pressure veins. The connection on the vein end of the graft, known as the graft-to-vein anastomosis, fails frequently and chronically due to high rates of stenosis and thrombosis. These failures are widely believed to be associated with pathologically high and low flow shear strain rates at the graft-to-vein anastomosis. We hypothesized that consistent with pipe flow dynamics and prior work exploring vein-to-artery anastomosis angles in arteriovenous fistulas, altering the graft-to-vein anastomosis angle can reduce the incidence of pathological shear rate fields. We tested this via computational fluid dynamic simulations of idealized arteriovenous grafts, using the Bird-Carreau constitutive law for blood. We observed that low graft-to-vein anastomosis angles ( > 40 ∘ ) led to increased incidence of pathologically high shear rates. Optimizations predicted that an intermediate ( ∼ 30 ∘ ) graft-to-anastomosis angle was optimal. Our study demonstrates that graft-to-vein anastomosis angles can significantly impact pathological flow fields, and can be optimized to substantially improve arteriovenous graft patency rates
Computational identification of Drosophila microRNA genes
BACKGROUND: MicroRNAs (miRNAs) are a large family of 21-22 nucleotide non-coding RNAs with presumed post-transcriptional regulatory activity. Most miRNAs were identified by direct cloning of small RNAs, an approach that favors detection of abundant miRNAs. Three observations suggested that miRNA genes might be identified using a computational approach. First, miRNAs generally derive from precursor transcripts of 70-100 nucleotides with extended stem-loop structure. Second, miRNAs are usually highly conserved between the genomes of related species. Third, miRNAs display a characteristic pattern of evolutionary divergence. RESULTS: We developed an informatic procedure called 'miRseeker', which analyzed the completed euchromatic sequences of Drosophila melanogaster and D. pseudoobscura for conserved sequences that adopt an extended stem-loop structure and display a pattern of nucleotide divergence characteristic of known miRNAs. The sensitivity of this computational procedure was demonstrated by the presence of 75% (18/24) of previously identified Drosophila miRNAs within the top 124 candidates. In total, we identified 48 novel miRNA candidates that were strongly conserved in more distant insect, nematode, or vertebrate genomes. We verified expression for a total of 24 novel miRNA genes, including 20 of 27 candidates conserved in a third species and 4 of 11 high-scoring, Drosophila-specific candidates. Our analyses lead us to estimate that drosophilid genomes contain around 110 miRNA genes. CONCLUSIONS: Our computational strategy succeeded in identifying bona fide miRNA genes and suggests that miRNAs constitute nearly 1% of predicted protein-coding genes in Drosophila, a percentage similar to the percentage of miRNAs recently attributed to other metazoan genomes
Hoopoe: Simulation of Extreme Programming
Experts agree that “smart” communication are an interesting new topic in the field of cryptography, and systems engineers concur. In our research, we verify the visualization of DNS [34]. In this paper we propose a novel system for the simulation of the memory bus (Hoopoe), which we use to disprove that suffix trees can be made self-learning, interposable, and ubiquitous
The Recurrent Eclipse of an Unusual Pre--Main-Sequence Star in IC 348
The recurrence of a previously documented eclipse of a solar-like
pre--main-sequence star in the young cluster IC 348 has been observed. The
recurrence interval is 4.7 yr and portions of 4 cycles have now been
seen. The duration of each eclipse is at least 3.5 years, or % of a
cycle, verifying that this is not an eclipse by a stellar companion. The light
curve is generally symmetric and approximately flat-bottomed. Brightness at
maximum and minimum have been rather stable over the years but the light curve
is not perfectly repetitive or smooth and small variations exist at all phases.
We confirm that the star is redder when fainter. Models are discussed and it is
proposed that this could be a system similar to KH 15D in NGC 2264.
Specifically, it may be an eccentric binary in which a portion of the orbit of
one member is currently occulted during some binary phases by a circumbinary
disk. The star deserves sustained observational attention for what it may
reveal about the circumstellar environment of low-mass stars of planet-forming
age.Comment: Accepted for publication in ApJ (Letters
CO\u3ci\u3e2\u3c/i\u3e Fixation Kinetics of \u3ci\u3eHalothiobacillus neapolitanus\u3c/i\u3e Mutant Carboxysomes Lacking Carbonic Anhydrase Suggest the Shell Acts as a Diffusional Barrier for CO\u3csub\u3e2\u3c/sub\u3e
The widely accepted models for the role of carboxysomes in the carbon-concentrating mechanism of autotrophic bacteria predict the carboxysomal carbonic anhydrase to be a crucial component. The enzyme is thought to dehydrate abundant cytosolic bicarbonate and provide ribulose 1.5-bisphosphate carboxylase/oxygenase (RubisCO) sequestered within the carboxysome with sufficiently high concentrations of its substrate, CO2, to permit its efficient fixation onto ribulose 1,5-bisphosphate. In this study, structure and function of carboxysomes purified from wild type Halothiobacillus neapolitanus and from a high CO2-requiring mutant that is devoid of carboxysomal carbonic anhydrase were compared. The kinetic constants for the carbon fixation reaction confirmed the importance of a functional carboxysomal carbonic anhydrase for efficient catalysis by RubisCO. Furthermore, comparisons of the reaction in intact and broken microcompartments and by purified carboxysomal RubisCO implicated the protein shell of the microcompartment as impeding diffusion of CO2 into and out of the carboxysome interior
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