29,439 research outputs found
Double-distribution-function discrete Boltzmann model for combustion
A 2-dimensional discrete Boltzmann model for combustion is presented.
Mathematically, the model is composed of two coupled discrete Boltzmann
equations for two species and a phenomenological equation for chemical reaction
process. Physically, the model is equivalent to a reactive Navier-Stokes model
supplemented by a coarse-grained model for the thermodynamic nonequilibrium
behaviours. This model adopts 16 discrete velocities. It works for both
subsonic and supersonic combustion phenomena with flexible specific heat ratio.
To discuss the physical accuracy of the coarse-grained model for nonequilibrium
behaviours, three other discrete velocity models are used for comparisons.
Numerical results are compared with analytical solutions based on both the
first-order and second-order truncations of the distribution function. It is
confirmed that the physical accuracy increases with the increasing moment
relations needed by nonequlibrium manifestations. Furthermore, compared with
the single distribution function model, this model can simulate more details of
combustion.Comment: Accepted for publication in Combustion and Flam
Wind energy system time-domain (WEST) analyzers
A portable analyzer which simulates in real time the complex nonlinear dynamics of horizontal axis wind energy systems was constructed. Math models for an aeroelastic rotor featuring nonlinear aerodynamic and inertial terms were implemented with high speed digital controllers and analog calculation. This model was combined with other math models of elastic supports, control systems, a power train and gimballed rotor kinematics. A stroboscopic display system graphically depicting distributed blade loads, motion, and other aerodynamic functions on a cathode ray tube is included. Limited correlation efforts showed good comparison between the results of this analyzer and other sophisticated digital simulations. The digital simulation results were successfully correlated with test data
Extracting and Stabilizing the Unstable State of Hysteresis Loop
A novel perturbation method for the stabilization of unstable intermediate
states of hysteresis loop (i.e. S-shaped curve) is proposed. This method only
needs output signals of the system to construct the perturbation form without
delay-coordinate embedding technique, it is more practical for real-world
systems. Stabilizing and tracking the unstable intermediate branch are
demonstrated through the examples of a bistable laser system and delay feedback
system. All the numerical results are obtained by simulating each of the real
experimential conditions.Comment: 6 pages, REVTEX, 4 ps figure
DSP based platform for an enhanced HF channel simulator
With the aim of improving existing tools for testing new HF transmission systems, this article describes a modification of the basic Watterson (1970) model which can be implemented without any extra added complexity with a general purpose DSP card running an a PC IBM compatible.Peer ReviewedPostprint (published version
On the Designing of Spikes Band-Pass Filters for FPGA
In this paper we present two implementations of spike-based bandpass
filters, which are able to reject out-of-band frequency components in the
spike domain. First one is based on the use of previously designed spike-based
low-pass filters. With this architecture the quality factor, Q, is lower than 0.5.
The second implementation is inspired in the analog multi-feedback filters
(MFB) topology, it provides a higher than 1 Q factor, and ideally tends to
infinite. These filters have been written in VHLD, and synthesized for FPGA.
Two spike-based band-pass filters presented take advantages of the spike rate
coded representation to perform a massively parallel processing without complex
hardware units, like floating point arithmetic units, or a large memory. These low
requirements of hardware allow the integration of a high number of filters inside
a FPGA, allowing to process several spike coded signals fully in parallel.Ministerio de Ciencia e Innovación TEC2009-10639-C04-0
Building Blocks for Spikes Signals Processing
Neuromorphic engineers study models and
implementations of systems that mimic neurons behavior in the
brain. Neuro-inspired systems commonly use spikes to
represent information. This representation has several
advantages: its robustness to noise thanks to repetition, its
continuous and analog information representation using digital
pulses, its capacity of pre-processing during transmission time,
... , Furthermore, spikes is an efficient way, found by nature, to
codify, transmit and process information. In this paper we
propose, design, and analyze neuro-inspired building blocks
that can perform spike-based analog filters used in signal
processing. We present a VHDL implementation for FPGA.
Presented building blocks take advantages of the spike rate
coded representation to perform a massively parallel processing
without complex hardware units, like floating point arithmetic
units, or a large memory. Those low requirements of hardware
allow the integration of a high number of blocks inside a FPGA,
allowing to process fully in parallel several spikes coded signals.Junta de Andalucía P06-TIC-O1417Ministerio de Ciencia e Innovación TEC2009-10639-C04-02Ministerio de Ciencia e Innovación TEC2006-11730-C03-0
Analysis of Diffusion of Ras2 in Saccharomyces cerevisiae Using Fluorescence Recovery after Photobleaching
Binding, lateral diffusion and exchange are fundamental dynamic processes
involved in protein association with cellular membranes. In this study, we
developed numerical simulations of lateral diffusion and exchange of
fluorophores in membranes with arbitrary bleach geometry and exchange of the
membrane localized fluorophore with the cytosol during Fluorescence Recovery
after Photobleaching (FRAP) experiments. The model simulations were used to
design FRAP experiments with varying bleach region sizes on plasma-membrane
localized wild type GFP-Ras2 with a dual lipid anchor and mutant GFP-Ras2C318S
with a single lipid anchor in live yeast cells to investigate diffusional
mobility and the presence of any exchange processes operating in the time scale
of our experiments. Model parameters estimated using data from FRAP experiments
with a 1 micron x 1 micron bleach region-of-interest (ROI) and a 0.5 micron x
0.5 micron bleach ROI showed that GFP-Ras2, single or dual lipid modified,
diffuses as single species with no evidence of exchange with a cytoplasmic
pool. This is the first report of Ras2 mobility in yeast plasma membrane. The
methods developed in this study are generally applicable for studying diffusion
and exchange of membrane associated fluorophores using FRAP on commercial
confocal laser scanning microscopes.Comment: Accepted for publication in Physical Biology (2010). 28 pages, 7
figures, 3 table
Applications of recurrent neural networks in batch reactors. Part I: NARMA modelling of the dynamic behaviour of the heat transfer fluid
This paper is focused on the development of nonlinear models, using artificial neural networks, able to provide appropriate predictions when acting as process simulators. The dynamic behaviour of the heat transfer fluid temperature in a jacketed chemical reactor has been selected as a case study. Different structures of NARMA (Non-linear ARMA) models have been studied. The experimental results have allowed to carry out a comparison between the different neural approaches and a first-principles model. The best neural results are obtained using a parallel model structure based on a recurrent neural network architecture, which guarantees better dynamic approximations than currently employed neural models. The results suggest that parallel models built up with recurrent networks can be seen as an alternative to phenomenological models for simulating the dynamic behaviour of the heating/cooling circuits which change from batch installation to installation.Publicad
Probing the Cosmic Gamma-Ray Burst Rate with Trigger Simulations of the Swift Burst Alert Telescope
The gamma-ray burst (GRB) rate is essential for revealing the connection
between GRBs, supernovae and stellar evolution. Additionally, the GRB rate at
high redshift provides a strong probe of star formation history in the early
universe. While hundreds of GRBs are observed by Swift, it remains difficult to
determine the intrinsic GRB rate due to the complex trigger algorithm of Swift.
Current studies of the GRB rate usually approximate the Swift trigger algorithm
by a single detection threshold. However, unlike the previously flown GRB
instruments, Swift has over 500 trigger criteria based on photon count rate and
additional image threshold for localization. To investigate possible systematic
biases and explore the intrinsic GRB properties, we develop a program that is
capable of simulating all the rate trigger criteria and mimicking the image
threshold. Our simulations show that adopting the complex trigger algorithm of
Swift increases the detection rate of dim bursts. As a result, our simulations
suggest bursts need to be dimmer than previously expected to avoid
over-producing the number of detections and to match with Swift observations.
Moreover, our results indicate that these dim bursts are more likely to be high
redshift events than low-luminosity GRBs. This would imply an even higher
cosmic GRB rate at large redshifts than previous expectations based on
star-formation rate measurements, unless other factors, such as the luminosity
evolution, are taken into account. The GRB rate from our best result gives a
total number of 4571^{+829}_{-1584} GRBs per year that are beamed toward us in
the whole universe.
SPECIAL NOTE (2015.05.16): This new version incorporates an erratum. All the
GRB rate normalizations () should be a factor of 2 smaller
than previously reported. Please refer to the Appendix for more details. We
sincerely apologize for the mistake.Comment: 52 pages, 17 figures, published in ApJ 783, 24L (2014). An erratum is
included. A typo in Eq. 8 is fixed in this versio
- …