831 research outputs found
A Nonlinear Dynamic Boiler Model accounting for Highly Variable Load Conditions
This paper describes a new nonlinear dynamic model for a natural circulation
boiler. The model is based on physical principles, i.e. mass, energy and
momentum balances. A systematic approach is followed leading to new insights
into the physics of drum water level and downcomer mass flow. The final model
captures fast dynamic responses that are necessary to describe the operation of
a boiler under highly variable load conditions. New features of the model
include (i) a multi-compartment model for the risers, (ii) a new model for drum
water level, and (iii) a new dynamic model for the flow of water in the
downcomers. Implications of the model for control system design are also
explored.Comment: 25 pages, 5 figures. Submitted to Automatic
Trapped-ion quantum error-correcting protocols using only global operations
Quantum error-correcting codes are many-body entangled states that are
prepared and measured using complex sequences of entangling operations. Each
element of such an entangling sequence introduces noise to delicate quantum
information during the encoding or reading out of the code. It is important
therefore to find efficient entangling protocols to avoid the loss of
information. Here we propose an experiment that uses only global entangling
operations to encode an arbitrary logical qubit to either the five-qubit
repetition code or the five-qubit code, with a six-ion Coulomb crystal
architecture in a Penning trap. We show that the use of global operations
enables us to prepare and read out these codes using only six and ten global
entangling pulses, respectively. The proposed experiment also allows the
acquisition of syndrome information during readout. We provide a noise analysis
for the presented protocols, estimating that we can achieve a six-fold
improvement in coherence time with noise as high as on each
entangling operation.Comment: 7 pages, 4 figures, published version, comments are welcom
Stochastic Adaptive Control for Exponentially Convergent Time-Varying Systems
This paper shows that the standard stochastic adaptive control algorithms for time-invariant systems have an inherent robustness property which renders them applicable, without modification, to time-varying systems whose parameters converge exponentially. One class of systems satisfying this requirement is those having non-steady-state Kalman filter or innovation representations. This allows the usual assumption of a stationary ARMAX representation to be replaced by a more general state space model.published_or_final_versio
The Quadratic Gaussian Rate-Distortion Function for Source Uncorrelated Distortions
We characterize the rate-distortion function for zero-mean stationary
Gaussian sources under the MSE fidelity criterion and subject to the additional
constraint that the distortion is uncorrelated to the input. The solution is
given by two equations coupled through a single scalar parameter. This has a
structure similar to the well known water-filling solution obtained without the
uncorrelated distortion restriction. Our results fully characterize the unique
statistics of the optimal distortion. We also show that, for all positive
distortions, the minimum achievable rate subject to the uncorrelation
constraint is strictly larger than that given by the un-constrained
rate-distortion function. This gap increases with the distortion and tends to
infinity and zero, respectively, as the distortion tends to zero and infinity.Comment: Revised version, to be presented at the Data Compression Conference
200
Assessing the coherence in biological and environmental drivers of young sea bass abundance across important estuarine nursery areas of the northern European sea bass stock
Year class strength is an important determinant of fish population size, but the drivers are often unknown. The northern stock of European sea bass (Dicentrarchus labrax) is an important target species for both commercial and recreational fisheries. Scientific assessments showed a rapid decline in spawning stock biomass from 2010-18 attributed to a combination of fishing mortality and poor year class strength. Recruitment to the adult stock is linked to the abundance and temporal dynamics of young bass in estuarine nursery areas, but little is known about the relative importance of environmental and biological drivers on the survival of these young life stages. In this study, we use Generalised Linear Models to attempt to identify important local environmental (sea surface temperature and river flow) and biological (chlorophyll-a concentration and predator abundance) drivers of young sea bass abundance. We focus on seven British and Irish estuarine areas that are important to the northern stock of European sea bass. In four English estuarine areas there were good model fits to the abundance of young sea bass, but predictors differed amongst these suggesting that drivers of abundance may differ among individual nursery areas. This was further demonstrated by poor fits of models generated for English estuaries to interannual patterns of abundance in the Irish nursery areas tested. The differences found in the most important abundance drivers amongst areas highlight the complex and differing dynamics between estuaries. If the number of young bass that eventually join the adult stock is dependent on survivors from a diverse set of unique nursery area conditions, then endeavours to incorporate this knowledge into fisheries management should be further explored
Genome sequence of the Ornithopus/Lupinus-nodulating Bradyrhizobium sp. strain WSM471
Bradyrhizobium sp. strain WSM471 is an aerobic, motile, Gram-negative, non-spore-forming rod that was isolated from an effective nitrogen-(N-2) fixing root nodule formed on the annual legume Ornithopus pinnatus (Miller) Druce growing at Oyster Harbour, Albany district, Western Australia in 1982. This strain is in commercial production as an inoculant for Lupinus and Ornithopus. Here we describe the features of Bradyrhizobium sp. strain WSM471, together with genome sequence information and annotation. The 7,784,016 bp high-quality-draft genome is arranged in 1 scaffold of 2 contigs, contains 7,372 protein-coding genes and 58 RNA-only encoding genes, and is one of 20 rhizobial genomes sequenced as part of the DOE Joint Genome Institute 2010 Community Sequencing Program
Structures in surface-brightness profiles of LMC and SMC star clusters: evidence of mergers?
The LMC and SMC are rich in binary star clusters, and some mergers are
expected. It is important to characterize single clusters, binary clusters and
candidates to mergers. We selected a sample of star clusters in each Cloud with
this aim. Surface photometry of 25 SMC and 22 LMC star clusters was carried
with the ESO Danish 1.54 m telescope. 23 clusters were observed for the first
time for these purposes. We fitted Elson, Fall and Freeman (1987, EFF) profiles
to the data, deriving structural parameters, luminosities and masses. We also
use isophotal maps to constrain candidates to cluster interactions.} {The
structural parameters, luminosities and masses presented good agreement with
those in the literature. Three binary clusters in the sample have a double
profile. Four clusters (NGC 376, K 50, K 54 and NGC 1810) do not have
companions and present as well important deviations from EFF profiles. The
present sample contains blue and red Magellanic clusters. Extended EFF profiles
were detected in some blue clusters. We find evidence that important deviations
from the body of EFF profiles might be used as a tool to detect cluster
mergers.Comment: 16 pages and 8 figures. Accepted by A&
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