206 research outputs found
Fourier Series Formalization in ACL2(r)
We formalize some basic properties of Fourier series in the logic of ACL2(r),
which is a variant of ACL2 that supports reasoning about the real and complex
numbers by way of non-standard analysis. More specifically, we extend a
framework for formally evaluating definite integrals of real-valued, continuous
functions using the Second Fundamental Theorem of Calculus. Our extended
framework is also applied to functions containing free arguments. Using this
framework, we are able to prove the orthogonality relationships between
trigonometric functions, which are the essential properties in Fourier series
analysis. The sum rule for definite integrals of indexed sums is also
formalized by applying the extended framework along with the First Fundamental
Theorem of Calculus and the sum rule for differentiation. The Fourier
coefficient formulas of periodic functions are then formalized from the
orthogonality relations and the sum rule for integration. Consequently, the
uniqueness of Fourier sums is a straightforward corollary.
We also present our formalization of the sum rule for definite integrals of
infinite series in ACL2(r). Part of this task is to prove the Dini Uniform
Convergence Theorem and the continuity of a limit function under certain
conditions. A key technique in our proofs of these theorems is to apply the
overspill principle from non-standard analysis.Comment: In Proceedings ACL2 2015, arXiv:1509.0552
Improved Sensor Fault-Tolerant Control Technique Applied to Three-Phase Induction Motor Drive
An improved fault-tolerant control (FTC) method using mathematical functions is applied to the induction motor drive (IMD) against current sensors and speed encoder failures, which occur when the sensor is disconnected or completely damaged. The IMD with two current sensors and an encoder is speed controlled based on the field-oriented control (FOC) technique in regular operation. In this paper, an FTC unit is implemented in the FOC controller to detect and solve the sensor fault to increase the reliability of the speed control process. The measured stator currents and the feedback speed signal are integrated into the diagnosis algorithms to create a sensor fault-tolerant control function. Three diagnosis functions operating in a defined sequence are proposed for determining the health status of current and speed sensors. The FTC function performs isolation and replaces the faulty sensor signals with the proper estimated signals; then, the IMD will operate in the corresponding sensorless mode. Simulations will be performed to verify the accuracy and reliability of the proposed method under various sensor faults
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A hierarchical approach to formal modeling and verification of asynchronous circuits
The self-timed (or asynchronous) approach to
circuit design has demonstrated benefits in a number of different
areas for its low energy consumption, high operating speed,
composability, and modularity. Nonetheless, the asynchronous paradigm
exposes challenges that are not found in the synchronous (or
clock-driven) paradigm. For the verification task, a challenge
emerges from the large number of potential operational interleavings
exhibited in the asynchronous paradigm. Simply exploring all
interleavings is, in general, intractable because the number of
interleavings can grow exponentially.
This dissertation focuses on developing scalable methods that are
capable of reasoning effectively about the interleaving problem
exhibited in self-timed systems. We specify and verify
finite-state-machine representations of self-timed circuit designs
using the DE system, a formal hardware description language defined
using the ACL2 theorem-proving system. We apply a link-joint paradigm
to model self-timed circuits as networks of channels that communicate
with each other locally via handshake protocols. This link-joint
model has been shown to be a universal model for various self-timed
circuit families. In addition, this model has a clean formalization
in the ACL2 logic and provides a protocol level that abstracts away
timing constraints at the circuit level.
Unlike many efforts for validating timing and communication properties
of self-timed systems, we are interested in verifying functional
properties. Specifically, we verify the functional correctness of
self-timed systems in terms of relationships between their input and
output sequences. To mitigate the consideration of all interleavings
simultaneously, we address the verification problem hierarchically and
avoid exploring the internal structures of verified submodules as well
as their operational interleavings. The input-output relationship of
a verified submodule is determined based on the communication signals
at the submodule's input and output ports, while abstracting away all
execution paths internal to that submodule.Computer Science
NOISE TRADER RISK: EVIDENCE FROM VIETNAM STOCK MARKET
Abstract: This paper investigates the existence of noise trader risk in Vietnam’s stock market and its effect on the daily returns of stock prices. The methodologies contain the estimation of GARCH (1,1) model to filter the residuals using the moving average method to calculate the impact of information traders. Noise trader risk or the risk that is caused by noise traders is derived by subtracting the residuals by the rational traders’ impact. We find that the noise trader risk does exist in Vietnam’s stock market and its impact on daily returns of stocks is unpredictable. Meanwhile, we find a positive impact of information traders on the stock returns. It increases the daily stock returns, and in turn, helps the market to correct itself because the stock prices move back to its fundamental value.Keywords: noise trader risk, GARCH (1,1), Vietnam’s stock marke
Poverty Assessment of Ethnic Minorities in Vietnam
Ethnic minorities in Vietnam have experienced high income fluctuation over time. This study aims to examine why a number of households experienced an income increase while others experienced an income decrease in poor areas with high density of ethnic minorities in Vietnam. It shows that the increase in household income results from an increase in average income per working hour. That is, the number of working hours did not change significantly but the increase in productivity per working hour helps households to increase their household income. In addition, the increase in number of working hour and increase in income transfers also contribute to the income increase. Our study also indicates that the increase in labor productivity mostly comes from agricultural sector but not from non-agricultural sector. For households with falling income, the major reasons for the income decrease are decreasing labor productivity, especially in agricultural sector
Loss to follow-up after pregnancy among Sub-Saharan Africa-born women living with HIV in England, Wales and Northern Ireland:results from a large national cohort
BACKGROUND: Little is known about retention in human immunodeficiency virus (HIV) care in HIV-positive women after pregnancy in the United Kingdom. We explored the association between loss to follow-up (LTFU) in the year after pregnancy, maternal place of birth and duration of UK residence, in HIV-positive women in England, Wales, and Northern Ireland. METHODS: We analyzed combined data from 2 national data sets: the National Study of HIV in Pregnancy and Childhood; and the Survey of Prevalent HIV Infections Diagnosed, including pregnancies in 2000 to 2009 in women with diagnosed HIV. Logistic regression models were fitted with robust standard errors to estimate adjusted odds ratios (AOR). RESULTS: Overall, 902 of 7211 (12.5%) women did not access HIV care in the year after pregnancy. Factors associated with LTFU included younger age, last CD4 in pregnancy of 350 cells/μL or greater and detectable HIV viral load at the end of pregnancy (all P < 0.001). On multivariable analysis, LTFU was more likely in sub-Saharan Africa-born (SSA-born) women than white UK-born women (AOR, 2.17; 95% confidence interval, 1.50–3.14; P < 0.001). The SSA-born women who had migrated to the UK during pregnancy were 3 times more likely than white UK-born women to be lost to follow-up (AOR, 3.19; 95% confidence interval, 1.94–3.23; P < 0.001). CONCLUSIONS: One in 8 HIV-positive women in England, Wales, and Northern Ireland did not return for HIV care in the year after pregnancy, with SSA-born women, especially those who migrated to the United Kingdom during pregnancy, at increased risk. Although emigration is a possible explanatory factor, disengagement from care may also play a role
ANTIMICROBIAL COMPOUNDS FROM RHIZOPHORA STYLOSA
(6S,7E,9R)-6,9-dihydroxy-4,7-megastiymadien-3-one 9-O-[α-L-arabinopyranosyl-(l→6)-β-D-glucopyranoside] (1), blumenol A (2), and kaempferol 3-rutinoside (3) were isolated from the methanol extract of the leaves of mangrove plant Rhizophora stylosa Griff. Structural elucidation of the metabolites was carried out by analysis of their spectroscopic data and by comparison with those reported in the literature. All these compounds exhibited antimicrobial activity and were isolated from this genus for the first time
A robust diagnosis method for speed sensor fault based on stator currents in the RFOC induction motor drive
A valid diagnosis method for the speed sensor failure (SSF) is an essential requirement to ensure the reliability of Fault-Tolerant Control (FTC) models in induction motor drive (IMD) systems. Most recent researches have focused on directly comparing the measured and estimated rotor speed signal to detect the speed sensor fault. However, using that such estimated value in both the fault diagnosis and the controller reconfiguration phases leads to the insufficient performance of FTC modes. In this paper, a novel diagnosis-technique based on the stator current model combined with a confusion prevention condition is proposed to detect the failure states of the speed sensor in the IMD systems. It helps the FTC mode to separate between the diagnosis and reconfiguration phases against a speed sensor fault. This proposed SSF diagnosis method can also effectively apply for IMs’ applications at the low-speed range where the speed sensor signal often suffers from noise. MATLAB/Simulink software has been used to implement the simulations in various speed ranges. The achieved results have demonstrated the capability and effectiveness of the proposed SSF method against speed sensor faults
Triterpenes and triterpene-glycoside from the leaves of Lawsonia inermis.
From the leaves of Lawsonia inermis (syn. L. alba), two triterpenes augustic acid (1) and 1b,2a,3a,19a-tetrahydroxy-12-ursen-28-oic acid (2), and a triterpene-glycoside suavissimoside R1 (3) were isolated by using various chromatoghraphies. Their structures were characterized on the basis of the spectroscopic data (1D-NMR, HSQC, HMBC, ESI-MS) in comparison with the literature. This is the first report of 1 - 3 from Lawsonia species. Keywords: Lawsonia inermis, Lythraceae, Triterpene
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