5,045 research outputs found
Distributed Optimization in Energy Harvesting Sensor Networks with Dynamic In-network Data Processing
Energy Harvesting Wireless Sensor Networks (EH- WSNs) have been attracting increasing interest in recent years. Most current EH-WSN approaches focus on sensing and net- working algorithm design, and therefore only consider the energy consumed by sensors and wireless transceivers for sensing and data transmissions respectively. In this paper, we incorporate CPU-intensive edge operations that constitute in-network data processing (e.g. data aggregation/fusion/compression) with sens- ing and networking; to jointly optimize their performance, while ensuring sustainable network operation (i.e. no sensor node runs out of energy). Based on realistic energy and network models, we formulate a stochastic optimization problem, and propose a lightweight on-line algorithm, namely Recycling Wasted Energy (RWE), to solve it. Through rigorous theoretical analysis, we prove that RWE achieves asymptotical optimality, bounded data queue size, and sustainable network operation. We implement RWE on a popular IoT operating system, Contiki OS, and eval- uate its performance using both real-world experiments based on the FIT IoT-LAB testbed, and extensive trace-driven simulations using Cooja. The evaluation results verify our theoretical analysis, and demonstrate that RWE can recycle more than 90% wasted energy caused by battery overflow, and achieve around 300% network utility gain in practical EH-WSNs
Evaluation of measurement technique for a precision aspheric artefact using a nano-measuring machine
A precision aspheric artefact is measured in 3D by a commercially available nano-measuring machine (NMM) integrated with a contact inductive sensor as the probe. The mathematics of 3D compensation of the error caused by the probe radius is derived. The influence of the probe radius measurement uncertainty on the compensation errors for the 3D measurements is discussed. If the calibration uncertainty of probe radius is 1m and 0.1 m respectively, the compensation errors for a paraboloid artefact are within 100 nm and 10 nm respectively, and the artefact measurement uncertainties are 103 nm and 26 nm respectively. The artefact calibration uncertainty depends more on the uncertainty of the probe radius calibration than the probe radius
Development of a high-speed H-alpha camera system for the observation of rapid fluctuations in solar flares
A solid-state digital camera was developed for obtaining H alpha images of solar flares with 0.1 s time resolution. Beginning in the summer of 1988, this system will be operated in conjunction with SMM's hard X-ray burst spectrometer (HXRBS). Important electron time-of-flight effects that are crucial for determining the flare energy release processes should be detectable with these combined H alpha and hard X-ray observations. Charge-injection device (CID) cameras provide 128 x 128 pixel images simultaneously in the H alpha blue wing, line center, and red wing, or other wavelength of interest. The data recording system employs a microprocessor-controlled, electronic interface between each camera and a digital processor board that encodes the data into a serial bitstream for continuous recording by a standard video cassette recorder. Only a small fraction of the data will be permanently archived through utilization of a direct memory access interface onto a VAX-750 computer. In addition to correlations with hard X-ray data, observations from the high speed H alpha camera will also be correlated and optical and microwave data and data from future MAX 1991 campaigns. Whether the recorded optical flashes are simultaneous with X-ray peaks to within 0.1 s, are delayed by tenths of seconds or are even undetectable, the results will have implications on the validity of both thermal and nonthermal models of hard X-ray production
Resolution and sensitivity of a Fabry-Perot interferometer with a photon-number-resolving detector
With photon-number resolving detectors, we show compression of interference
fringes with increasing photon numbers for a Fabry-Perot interferometer. This
feature provides a higher precision in determining the position of the
interference maxima compared to a classical detection strategy. We also
theoretically show supersensitivity if N-photon states are sent into the
interferometer and a photon-number resolving measurement is performed.Comment: 8 pages, 12 figures, 1 table, minor extensions, title changed, new
figures added, reference correcte
Collapse and Fragmentation of Molecular Cloud Cores. X. Magnetic Braking of Prolate and Oblate Cores
The collapse and fragmentation of initially prolate and oblate, magnetic
molecular clouds is calculated in three dimensions with a gravitational,
radiative hydrodynamics code. The code includes magnetic field effects in an
approximate manner: magnetic pressure, tension, braking, and ambipolar
diffusion are all modelled. The parameters varied for both the initially
prolate and oblate clouds are the initial degree of central concentration of
the radial density profile, the initial angular velocity, and the efficiency of
magnetic braking (represented by a factor or ). The
oblate cores all collapse to form rings that might be susceptible to
fragmentation into multiple systems. The outcome of the collapse of the prolate
cores depends strongly on the initial density profile. Prolate cores with
central densities 20 times higher than their boundary densities collapse and
fragment into binary or quadruple systems, whereas cores with central densities
100 times higher collapse to form single protostars embedded in bars. The
inclusion of magnetic braking is able to stifle protostellar fragmentation in
the latter set of models, as when identical models were calculated without
magnetic braking (Boss 2002), those cores fragmented into binary protostars.
These models demonstrate the importance of including magnetic fields in studies
of protostellar collapse and fragmentation, and suggest that even when magnetic
fields are included, fragmentation into binary and multiple systems remains as
a possible outcome of protostellar collapse.Comment: 20 pages, 8 figures. Astrophysical Journal, in pres
SEQOPTICS: a protein sequence clustering system
BACKGROUND: Protein sequence clustering has been widely used as a part of the analysis of protein structure and function. In most cases single linkage or graph-based clustering algorithms have been applied. OPTICS (Ordering Points To Identify the Clustering Structure) is an attractive approach due to its emphasis on visualization of results and support for interactive work, e.g., in choosing parameters. However, OPTICS has not been used, as far as we know, for protein sequence clustering. RESULTS: In this paper, a system of clustering proteins, SEQOPTICS (SEQuence clustering with OPTICS) is demonstrated. The system is implemented with Smith-Waterman as protein distance measurement and OPTICS at its core to perform protein sequence clustering. SEQOPTICS is tested with four data sets from different data sources. Visualization of the sequence clustering structure is demonstrated as well. CONCLUSION: The system was evaluated by comparison with other existing methods. Analysis of the results demonstrates that SEQOPTICS performs better based on some evaluation criteria including Jaccard coefficient, Precision, and Recall. It is a promising protein sequence clustering method with future possible improvement on parallel computing and other protein distance measurements
Thermal error modelling of machine tools based on ANFIS with fuzzy c-means clustering using a thermal imaging camera
Thermal errors are often quoted as being the largest contributor to CNC machine tool errors, but they can be effectively reduced using error compensation. The performance of a thermal error compensation system depends on the accuracy and robustness of the thermal error model and the quality of the inputs to the model. The location of temperature measurement must provide a representative measurement of the change in temperature that will affect the machine structure. The number of sensors and their locations are not always intuitive and the time required to identify the optimal locations is often prohibitive, resulting in compromise and poor results.
In this paper, a new intelligent compensation system for reducing thermal errors of machine tools using data obtained from a thermal imaging camera is introduced. Different groups of key temperature points were identified from thermal images using a novel schema based on a Grey model GM (0, N) and Fuzzy c-means (FCM) clustering method. An Adaptive Neuro-Fuzzy Inference System with Fuzzy c-means clustering (FCM-ANFIS) was employed to design the thermal prediction model. In order to optimise the approach, a parametric study was carried out by changing the number of inputs and number of membership functions to the FCM-ANFIS model, and comparing the relative robustness of the designs. According to the results, the FCM-ANFIS model with four inputs and six membership functions achieves the best performance in terms of the accuracy of its predictive ability. The residual value of the model is smaller than ± 2 μm, which represents a 95% reduction in the thermally-induced error on the machine. Finally, the proposed method is shown to compare favourably against an Artificial Neural Network (ANN) model
- …