3,230 research outputs found
Location and Orientation Optimisation for Spatially Stretched Tripole Arrays Based on Compressive Sensing
The design of sparse spatially stretched tripole
arrays is an important but also challenging task and this paper
proposes for the very first time efficient solutions to this problem.
Unlike for the design of traditional sparse antenna arrays, the
developed approaches optimise both the dipole locations and
orientations. The novelty of the paper consists in formulating
these optimisation problems into a form that can be solved by the
proposed compressive sensing and Bayesian compressive sensing
based approaches. The performance of the developed approaches
is validated and it is shown that accurate approximation of a
reference response can be achieved with a 67% reduction in the
number of dipoles required as compared to an equivalent uniform
spatially stretched tripole array, leading to a significant reduction
in the cost associated with the resulting arrays
Dual-Satellite Source Geolocation with Time and Frequency Offsets and Satellite Location Errors
This paper considers locating a static source on Earth using the time difference of arrival (TDOA) and frequency difference of arrival (FDOA) measurements obtained by a dual-satellite geolocation system. The TDOA and FDOA from the source are subject to unknown time and frequency offsets because the two satellites are imperfectly time-synchronized or frequency-locked. The satellite locations are not known accurately as well. To make the source position identifiable and mitigate the effect of satellite location errors, calibration stations at known positions are used. Achieving the maximum likelihood (ML) geolocation performance usually requires jointly estimating the source position and extra variables (i.e., time and frequency offsets as well as satellite locations), which is computationally intensive. In this paper, a novel closed-form geolocation algorithm is proposed. It first fuses the TDOA and FDOA measurements from the source and calibration stations to produce a single pair of TDOA and FDOA for source geolocation. This measurement fusion step eliminates the time and frequency offsets while taking into account the presence of satellite location errors. The source position is then found via standard TDOA-FDOA geolocation. The developed algorithm has low complexity and performance analysis shows that it attains the CrameΜr-Rao lower bound (CRLB) under Gaussian noises and mild conditions. Simulations using a challenging scenario with a short-baseline dual-satellite system verify the theoretical developments and demonstrate the good performance of the proposed algorithm
Tracking with Sparse and Correlated Measurements via a Shrinkage-based Particle Filter
This paper presents a shrinkage-based particle filter
method for tracking a mobile user in wireless networks. The
proposed method estimates the shadowing noise covariance
matrix using the shrinkage technique. The particle filter is
designed with the estimated covariance matrix to improve the
tracking performance. The shrinkage-based particle filter can
be applied in a number of applications for navigation, tracking
and localization when the available sensor measurements are
correlated and sparse. The performance of the shrinkage-based
particle filter is compared with the posterior Cramer-Rao lower
bound, which is also derived in the paper. The advantages
of the proposed shrinkage-based particle filter approach are
demonstrated via simulation and experimental results
Simulation of the soil water balance of wheat using daily weather forecast messages to estimate the reference evapotranspiration
Abstract. Aiming at developing real time water balance
modelling for irrigation scheduling, this study assesses the
accuracy of using the reference evapotranspiration (ETo) estimated
from daily weather forecast messages (ETo,WF) as
model input. A previous study applied to eight locations in
China (Cai et al., 2007) has shown the feasibility for estimating
ETo,WF with the FAO Penman-Monteith equation using
daily forecasts of maximum and minimum temperature,
cloudiness and wind speed. In this study, the global radiation
is estimated from the difference between the forecasted maximum
and minimum temperatures, the actual vapour pressure
is estimated from the forecasted minimum temperature
and the wind speed is obtained from converting the common
wind scales into wind speed. The present application
refers to a location in the North China Plain, Daxing, for the
wheat crop seasons of 2005β2006 and 2006β2007. Results
comparing ETo,WF with ETo computed with observed data
(ETo,obs) have shown favourable goodness of fitting indicators
and a RMSE of 0.77mmdβ1. ETo was underestimated
in the first year and overestimated in the second. The water
balance model ISAREG was calibrated with data from
four treatments for the first season and validated with data of
five treatments in the second season using observed weather
data. The calibrated crop parameters were used in the simulations
of the same treatments using ETo,WF as model input.
Errors in predicting the soil water content are small, 0.010
and 0.012m3 mβ3, respectively for the first and second year.
Other indicators also confirm the goodness of model predictions.
It could be concluded that using ETo computed from
daily weather forecast messages provides for accurate model
predictions and to use an irrigation scheduling model in real
tim
Quark Effects in the Gluon Condensate Contribution to the Scalar Glueball Correlation Function
One-loop quark contributions to the dimension-four gluon condensate term in
the operator product expansion (OPE) of the scalar glueball correlation
function are calculated in the MS-bar scheme in the chiral limit of quark
flavours. The presence of quark effects is shown not to alter the cancellation
of infrared (IR) singularities in the gluon condensate OPE coefficients. The
dimension-four gluonic condensate term represents the leading power corrections
to the scalar glueball correlator and, therein, the one-loop logarithmic
contributions provide the most important condensate contribution to those QCD
sum-rules independent of the low-energy theorem (the subtracted sum-rules).Comment: latex2e, 6 pages, 7 figures embedded in latex fil
Compressive Properties of SiC Particle-Reinforced Aluminum Matrix Composites under Repeated Impact Loading
Under repeated impact loading, SiC particle-reinforced aluminum matrix composites (SiCp/Al) experience severe plastic strains, which can lead to local changes in their microstructure. Microstructure variations have a significant effect on the dynamic behavior of SiCp/Al composites under subsequent impact loading. Their microstructure was analyzed by scanning electron microscopy (SEM). Then the dynamic compressive properties of SiCp/Al composites were studied using the split Hopkinson pressure bar (SHPB), and the dynamic compression stressβstrain curve for each impact was plotted.Π ΡΡΠ»ΠΎΠ²ΠΈΡΡ
ΠΏΠΎΠ²ΡΠΎΡΠ½ΠΎΠ³ΠΎ ΡΠ΄Π°ΡΠ½ΠΎΠ³ΠΎ Π½Π°Π³ΡΡΠΆΠ΅Π½ΠΈΡ ΠΊΠΎΠΌΠΏΠΎΠ·ΠΈΡΠΈΠΎΠ½Π½ΡΠ΅ ΠΌΠ°ΡΠ΅ΡΠΈΠ°Π»Ρ Ρ Π°Π»ΡΠΌΠΈΠ½ΠΈΠ΅Π²ΠΎΠΉ ΠΌΠ°ΡΡΠΈΡΠ΅ΠΉ, ΡΠΏΡΠΎΡΠ½Π΅Π½Π½ΡΠ΅ ΡΠ°ΡΡΠΈΡΠ°ΠΌΠΈ SiC (SiCp/Al), ΠΈΡΠΏΡΡΡΠ²Π°ΡΡ Π΄Π΅ΠΉΡΡΠ²ΠΈΠ΅ Π²ΡΡΠΎΠΊΠΈΡ
ΠΏΠ»Π°ΡΡΠΈΡΠ΅ΡΠΊΠΈΡ
Π΄Π΅ΡΠΎΡΠΌΠ°ΡΠΈΠΉ, ΡΡΠΎ ΠΌΠΎΠΆΠ΅Ρ ΠΏΡΠΈΠ²ΠΎΠ΄ΠΈΡΡ ΠΊ Π»ΠΎΠΊΠ°Π»ΡΠ½ΡΠΌ ΠΈΠ·ΠΌΠ΅Π½Π΅Π½ΠΈΡΠΌ ΠΈΡ
ΠΌΠΈΠΊΡΠΎΡΡΡΡΠΊΡΡΡΡ. ΠΠ·ΠΌΠ΅Π½Π΅Π½ΠΈΡ ΠΌΠΈΠΊΡΠΎΡΡΡΡΠΊΡΡΡΡ ΠΎΠΊΠ°Π·ΡΠ²Π°ΡΡ ΡΡΡΠ΅ΡΡΠ²Π΅Π½Π½ΠΎΠ΅ Π²Π»ΠΈΡΠ½ΠΈΠ΅ Π½Π° Π΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΎΠ΅ ΠΏΠΎΠ²Π΅Π΄Π΅Π½ΠΈΠ΅ ΠΊΠΎΠΌΠΏΠΎΠ·ΠΈΡΠΈΠΎΠ½Π½ΡΡ
ΠΌΠ°ΡΠ΅ΡΠΈΠ°Π»ΠΎΠ² SiCp/Al ΠΏΡΠΈ ΠΏΠΎΡΠ»Π΅Π΄ΡΡΡΠ΅ΠΌ ΡΠ΄Π°ΡΠ½ΠΎΠΌ Π½Π°Π³ΡΡΠΆΠ΅Π½ΠΈΠΈ. ΠΡ
ΠΌΠΈΠΊΡΠΎΡΡΡΡΠΊΡΡΡΠ° ΠΏΡΠΎΠ°Π½Π°Π»ΠΈΠ·ΠΈΡΠΎΠ²Π°Π½Π° Ρ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ΠΈΠ΅ΠΌ ΡΠΊΠ°Π½ΠΈΡΡΡΡΠ΅ΠΉ ΡΠ»Π΅ΠΊΡΡΠΎΠ½Π½ΠΎΠΉ ΠΌΠΈΠΊΡΠΎΡΠΊΠΎΠΏΠΈΠΈ. ΠΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΡΡ ΡΠΆΠΈΠΌΠ°Π΅ΠΌΠΎΡΡΡ ΠΊΠΎΠΌΠΏΠΎΠ·ΠΈΡΠΈΠΎΠ½Π½ΡΡ
ΠΌΠ°ΡΠ΅ΡΠΈΠ°Π»ΠΎΠ² ΠΈΠ·ΡΡΠ°Π»ΠΈ Ρ ΠΏΠΎΠΌΠΎΡΡΡ ΡΠ°Π·ΡΠ΅Π·Π½ΠΎΠ³ΠΎ ΡΡΠ΅ΡΠΆΠ½Ρ ΠΠΎΠΏΠΊΠΈΠ½ΡΠΎΠ½Π°, Π±ΡΠ»Π° ΠΏΠΎΡΡΡΠΎΠ΅Π½Π° Π·Π°Π²ΠΈΡΠΈΠΌΠΎΡΡΡ Π΄Π΅ΡΠΎΡΠΌΠ°ΡΠΈΠΈ ΠΎΡ Π΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΡΠΆΠΈΠΌΠ°ΡΡΠ΅Π³ΠΎ Π½Π°ΠΏΡΡΠΆΠ΅Π½ΠΈΡ Π΄Π»Ρ ΠΊΠ°ΠΆΠ΄ΠΎΠ³ΠΎ ΡΠ΄Π°ΡΠ½ΠΎΠ³ΠΎ Π²ΠΎΠ·Π΄Π΅ΠΉΡΡΠ²ΠΈΡ
Existence and uniqueness of solutions for systems of fractional differential equations with RiemannβStieltjes integral boundary condition
In this article, we first establish an existence and uniqueness result for a class of systems of nonlinear operator equations under more general conditions by means of the cone theory and monotone iterative technique. Furthermore, the iterative sequence of the solution and the error estimation of the system are given. Then we use this new result to study the existence and uniqueness of the solution for boundary value problems of systems of fractional differential equations with a RiemannβStieltjes integral boundary condition in real Banach spaces. The results obtained in this paper are more general than many previous results and complement them
More arrows in the ancient DNA quiver: use of paleoepigenomes and paleomicrobiomes to investigate animal adaptation to environment
Whether and how epigenetic mechanisms and the microbiome play a role in mammalian adaptation raised considerable attention and controversy, mainly because they have the potential to add new insights into the Modern Synthesis. Recent attempts to reconcile neo-Darwinism and neo-Lamarckism in a unified theory of molecular evolution give epigenetic mechanisms and microbiome a prominent role. However, supporting empirical data is still largely missing. Because experimental studies using extant animals can hardly be done over evolutionary timescales, we propose that advances in ancient DNA techniques provide a valid alternative. In this piece, we evaluate: (1) the possible roles of epigenomes and microbiomes in animal adaptation; (2) advances in the retrieval of paleoepigenome and paleomicrobiome data using ancient DNA techniques; and (3) the plasticity of either and interactions between the epigenome and the microbiome, while emphasising that it is essential to take both into account, as well as the underlying genetic factors that may confound the findings. We propose that advanced ancient DNA techniques should be applied to a wide range of past animals, so novel dynamics in animal evolution and adaption can be revealed.Yichen Liu, Laura S Weyrich, Bastien Llama
Crosstalk between MSH2βMSH3 and polΞ² promotes trinucleotide repeat expansion during base excision repair
Studies in knockout mice provide evidence that MSH2βMSH3 and the BER machinery promote trinucleotide repeat (TNR) expansion, yet how these two different repair pathways cause the mutation is unknown. Here we report the first molecular crosstalk mechanism, in which MSH2βMSH3 is used as a component of the BER machinery to cause expansion. On its own, pol Ξ² fails to copy TNRs during DNA synthesis, and bypasses them on the template strand to cause deletion. Remarkably, MSH2βMSH3 not only stimulates pol Ξ² to copy through the repeats but also enhances formation of the flap precursor for expansion. Our results provide direct evidence that MMR and BER, operating together, form a novel hybrid pathway that changes the outcome of TNR instability from deletion to expansion during the removal of oxidized bases. We propose that cells implement crosstalk strategies and share machinery when a canonical pathway is ineffective in removing a difficult lesion
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