Loading...
Search for:
sampling
0.009 seconds
Total 751 records
Economic-statistical design of simple linear profiles with variable sampling interval
, Article Journal of Applied Statistics ; Volume 43, Issue 8 , 2016 , Pages 1400-1418 ; 02664763 (ISSN) ; Noorossana, R ; Akhavan Niaki, S. T ; Sharif University of Technology
Taylor and Francis Ltd
2016
Abstract
Control charts are statistical tools to monitor a process or a product. However, some processes cannot be controlled by monitoring a characteristic; instead, they need to be monitored using profiles. Economic-statistical design of profile monitoring means determining the parameters of a profile monitoring scheme such that total costs are minimized while statistical measures maintain proper values. While varying sampling interval usually increases the effectiveness of profile monitoring, economic-statistical design of variable sampling interval (VSI) profile monitoring is investigated in this paper. An extended Lorenzen–Vance function is used for modeling total costs in VSI model where the...
Bounds on discrete fourier transform of random mask
, Article 2017 12th International Conference on Sampling Theory and Applications, SampTA 2017, 3 July 2017 through 7 July 2017 ; 2017 , Pages 327-330 ; 9781538615652 (ISBN) ; Marvasti, F ; Anbarjafari, G ; Kivinukk, A ; Tamberg, G ; Sharif University of Technology
Abstract
This paper proposes some bounds on maximum of magnitude of a random mask in Fourier domain. The random mask is used in random sampling scheme. Having a bound on the maximum value of a random mask in Fourier domain is very useful for some iterative recovery methods that use thresholding operator. In this paper, we propose some different bounds and compare them with the empirical examples. © 2017 IEEE
A magnetic multifunctional dendrimeric coating on a steel fiber for solid phase microextraction of chlorophenols
, Article Microchimica Acta ; Volume 184, Issue 7 , 2017 , Pages 2201-2209 ; 00263672 (ISSN) ; Manouchehri, M ; Allahdadlalouni, M ; Sharif University of Technology
Springer-Verlag Wien
2017
Abstract
A polyamidoamine dendrimer was synthesized, placed on magnetite nanoparticles, and the resulting material was then employed as a fiber coating for use in solid phase microextraction of chlorophenols. The polyamidoamine was expected to be an efficient extracting medium due to the presence of multipolar groups and its inner porosity. A thin stainless steel wire was coated with the dendritic polyamidoamine polymer via electrolysis and chemical reactions. The coated fiber was investigated in terms of headspace solid phase microextraction of chlorophenols from aqueous samples followed by GC-MS quantitation. The calibration plots are linear in the 2–1000 ng⋅L−1 chlorophenol concentration ranges....
Nanostructured molybdenum oxide in a 3D metal organic framework and in a 2D polyoxometalate network for extraction of chlorinated benzenes prior to their quantification by GC–MS
, Article Microchimica Acta ; Volume 185, Issue 12 , 2018 ; 00263672 (ISSN) ; Karimi Zandian, F ; Javanmardi, H ; Abbasi, A ; Golzari Aqda, T ; Sharif University of Technology
Abstract
A three–dimensional metal organic framework (3D–MOF) and a two–dimensional polyoxometalate (2D–POM), both incorporating nanostructured molybdenum (VI) oxide, were synthesized and implemented for headspace needle trap extraction of traces of chlorobenzenes (CBs). The 3D–MOF of type {(Mo2O6)(4,4′–bpy)}n and the 2D–POM of type [4,4′–bpy][Mo7O22] were synthesized by a solvothermal process and characterized by FT–IR, powder X–ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetry, energy dispersive X–ray, elemental mapping and Brunner–Emmet–Teller adsorption analyses. The 3D–MOF proved to be superior. Following thermal desorption, the CBs...
Evaluation of prepared natural polymers in the extraction of chlorobenzenes from environmental samples: sol–gel–based cellulose acetate-phenyltriethoxysilane fibers
, Article Microchemical Journal ; Volume 142 , 2018 , Pages 265-272 ; 0026265X (ISSN) ; Golzari Aqda, T ; Enteshari Najafabadi, M ; Sharif University of Technology
Abstract
In this research, three fibers including cellulose acetate (CA), CA–phenyltriethoxysilane (PTES) prepared via sol–gel electrospinning and sol–gel–based CA fibers immersed in PTES solution (dipped–CA–PTES) were prepared. The composition and morphology of the prepared fibers were evaluated by energy dispersive X-ray spectroscopy and field emission scanning electron microscopy. The prepared fibers were implemented in a home–made needle trap device, followed by thermal desorption of the selected chlorobenzenes (CBs) to a gas chromatography–flame ionization detector. Finally, parameters affecting the extraction methodology such as the amount of sorbent, extraction time and temperature, desorption...
Three-dimensional nanofiber scaffolds are superior to two-dimensional mats in micro-oriented extraction of chlorobenzenes
, Article Microchimica Acta ; Volume 185, Issue 7 , 2018 ; 00263672 (ISSN) ; Manshaei, F ; Rezvani, O ; Sharif University of Technology
Springer-Verlag Wien
2018
Abstract
Three-dimensional (3D) polyamide scaffolds were fabricated by applying a solvent bath as the collecting element. Electrospun nanofibers were immersed into the solvent bath to give a material with a laminated 3D texture. In parallel, 2D nanofibers were synthesized and utilized as microextractive phases in a needle trap device to compare the capabilities of 2D and 3D materials in terms of headspace extraction of various chlorobenzenes (chlorobenzene, 1,2-dichlorobenzene, 1,4-dichlorobenzene, 1,2,4-trichlorobenzene and 1,2,3,4-tetrachlorobenzene). The results demonstrate the superiority of 3D nanofibrous scaffolds over 2D mats. The porosity, morphology, and thermal stability of the 3D scaffolds...
Remedial measures to lessen the effect of imprecise measurement with linearly increasing variance on the performance of the MAX-EWMAMS scheme
, Article Arabian Journal for Science and Engineering ; Volume 43, Issue 6 , June , 2018 , Pages 3151-3162 ; 2193567X (ISSN) ; Maleki, M. R ; Akhavan Niaki, S. T ; Sharif University of Technology
Springer Verlag
2018
Abstract
Simultaneous monitoring of process mean and variability by a single control chart has been increasingly taken into consideration in recent years. However, the effect of imprecise measurements on the performances of some existing control schemes has been neglected. In this paper, the effect of measurement errors with linearly increasing variance on the detecting and diagnosing capability of the MAX-EWMAMS control chart is first investigated in Phase II monitoring. The results obtained using simulation studies show that the measurement errors affect the two performances of the chart, significantly. Then, two remedial measures including the ranked set sampling approach and using a larger sample...
Influence of finite time step in estimating of the kramers–moyal coefficients
, Article Understanding Complex Systems ; 2019 , Pages 191-205 ; 18600832 (ISSN) ; Sharif University of Technology
Springer Verlag
2019
Abstract
Data sampled at discrete times appear as successions of discontinuous jump events, even if the underlying trajectory is continuous. In this chapter we study finite sampling τ expansion of the Kramers-Moyal conditional moments for the Langevin and jump-diffusion dynamics. Using the expansion for the Langevin dynamics, we introduce a criterion to validate the method numerically, namely, the Pawula theorem, to judge whether the fourth-order KM moment tends to zero. The criterion is a relation between the fourth- and second-order KM conditional moments for small time lag τ [1]. © 2019, Springer Nature Switzerland AG
What factors results in having a severe crash? a closer look on distraction-related factors
, Article Cogent Engineering ; Volume 6, Issue 1 , 2019 ; 23311916 (ISSN) ; Mahmoudzadeh, A ; Kermanshah, M ; Sharif University of Technology
Cogent OA
2019
Abstract
This study provides a comprehensive literature review to summarize all contributing factors and the logit-based models that were used to predict the severity of crashes. Using the General Estimates Systems (GES) dataset, as a subset and a branch of the National Automotive Sampling System in the US, a Generalized Ordered Logit (GLM) model is developed to predict the crash severity. The developed severity model detects the most important parameters based on characteristics of the driver, the environment, the vehicle, the road, and the type of crash. This study aims to take a more in-depth look into the distraction-related factors as one of the most important groups of contributing factors to...
Influence of finite time step in estimating of the kramers–moyal coefficients
, Article Understanding Complex Systems ; 2019 , Pages 191-205 ; 18600832 (ISSN) ; Sharif University of Technology
Springer Verlag
2019
Abstract
Data sampled at discrete times appear as successions of discontinuous jump events, even if the underlying trajectory is continuous. In this chapter we study finite sampling τ expansion of the Kramers-Moyal conditional moments for the Langevin and jump-diffusion dynamics. Using the expansion for the Langevin dynamics, we introduce a criterion to validate the method numerically, namely, the Pawula theorem, to judge whether the fourth-order KM moment tends to zero. The criterion is a relation between the fourth- and second-order KM conditional moments for small time lag τ [1]. © 2019, Springer Nature Switzerland AG
A conjugate gradient sampling method for nonsmooth optimization
, Article 4OR ; Volume 18, Issue 1 , May , 2020 , Pages 73-90 ; Shaeiri, M ; Sharif University of Technology
Springer
2020
Abstract
We present an algorithm for minimizing locally Lipschitz functions being continuously differentiable in an open dense subset of Rn. The function may be nonsmooth and/or nonconvex. The method makes use of a gradient sampling method along with a conjugate gradient scheme. To find search directions, we make use of a sequence of positive definite approximate Hessians based on conjugate gradient matrices. The algorithm benefits from a restart procedure to improve upon poor search directions or to make sure that the approximate Hessians remain bounded. The global convergence of the algorithm is established. An implementation of the algorithm is executed on a collection of well-known test problems....
Some nonlinear/adaptive methods for fast recovery of the missing samples of signals
, Article Signal Processing ; Volume 88, Issue 3 , 2008 , Pages 624-638 ; 01651684 (ISSN) ; Jahani Yekta, M. M ; Marvasti, F ; Sharif University of Technology
2008
Abstract
In this paper an iterative method for recovery of the missing samples of signals is investigated in detail, and some novel linear, nonlinear, and adaptive extrapolation techniques are proposed to be used along with it to increase the convergence rate of the recovery system. The proposed methods would remarkably speed up the convergence rate, save processing power, and reduce the delay of the system compared to some well known accelerated versions of the aforementioned iterative algorithm. © 2007 Elsevier B.V. All rights reserved
Sensor module for multi-channel wireless photoplethysmography system
, Article 2007 5th Student Conference on Research and Development, SCORED, Selangor, 11 December 2007 through 12 December 2007 ; 2007 ; 1424414709 (ISBN); 9781424414703 (ISBN) ; Mohd Ali, M. A ; Zahedi, E ; Sharif University of Technology
2007
Abstract
The digital sensor module is developed to sample the input signal fed from a photo-sensor probe at sampling times ranging from 400-4000 μs equivalent to sampling rates of 2500-250 sample/second (S/s), respectively. The module produces 16-bit data packets which are transmitted serially and plotted to output the photoplethysmography signal (PPG). It displays accurate sampling values (packets) similar to the calculated ones. ©2007 IEEE
Supplier selection and order allocation in CLSC configuration with various supply strategies under disruption risk
, Article OPSEARCH ; Volume 57, Issue 3 , 2020 , Pages 908-934 ; Ghalehkhondabi, I ; Rafiee, M ; Namdar Zanganeh, S ; Sharif University of Technology
Springer
2020
Abstract
Supplier selection and order allocation are important keys for reverse logistics and closed-loop supply chain networks especially with the presence of demand–supply imbalance risks. If such uncertainties and risks are not foreseen in the chain, and corresponding appropriate measures are not taken to handle them, irreparable damages would be expected consequently. The importance of this issue in closed-loop supply chains is more appreciated due to the importance and the effect of this chain on the environment. In this research, the disruption risk and the uncertainties related to the demand, market price, and the number of returned products are simultaneously considered. Purchasing from the...
Simulation and control of an aromatic distillation column
, Article Iranian Journal of Chemistry and Chemical Engineering ; Volume 26, Issue 2 , 2007 , Pages 97-108 ; 10219986 (ISSN) ; Shahrokhi, M ; Sharif University of Technology
2007
Abstract
In general, the objective of distillation control is to maintain the desired products quality. In this paper, the performances of different one point control strategies for an aromatic distillation column have been compared through dynamic simulation. These methods are: a) Composition control using measured composition directly. This method sufferes from large sampling delay of measuring devices, b) Composition control by controlling the temperature of a specific tray. In this strategy, the composition-temperature relationship is used to find the temperature setpoint corresponding to the desired composition. Since composition-temperature relation depends on feed condition, an artificial...
A study on the mechanical properties of graphene oxide/epoxy nanocomposites
, Article Polymers and Polymer Composites ; Volume 29, Issue 9_suppl , 2021 , Pages S556-S564 ; 09673911 (ISSN) ; Moghim, M. H ; Eqra, N ; Sharif University of Technology
SAGE Publications Ltd
2021
Abstract
The aims of this research are to elucidate the role of graphene oxide on the mechanical properties of epoxy and also to obtain an equation for the modeling of its behavior. Accordingly, graphene oxide/epoxy nanocomposite samples are fabricated using the solution casting method. Tensile, flexural, SEM and FTIR tests are conducted on epoxy and the nanocomposite samples afterwards. The obtained results show that the tensile strength of epoxy improves even at low contents of graphene oxide such that 0.3 wt.% of GO yields an improvement of approximately 11.5%. The flexural strength of epoxy is also enhanced by 5.8% with 0.5 wt.% GO. Then, it decreases due to the agglomeration with increasing the...
On statistical learning of simplices: Unmixing problem revisited
, Article Annals of Statistics ; Volume 49, Issue 3 , 2021 , Pages 1626-1655 ; 00905364 (ISSN) ; Ilchi, S ; Saberi, A. H ; Motahari, S. A ; Hossein Khalaj, B ; Rabiee, H. R ; Sharif University of Technology
Institute of Mathematical Statistics
2021
Abstract
We study the sample complexity of learning a high-dimensional simplex from a set of points uniformly sampled from its interior. Learning of simplices is a long studied problem in computer science and has applications in computational biology and remote sensing, mostly under the name of “spectral unmixing.” We theoretically show that a sufficient sample complexity for reliable learning of a K-dimensional simplex up to a total-variation error of ε is O(Kε2 log Kε ), which yields a substantial improvement over existing bounds. Based on our new theoretical framework, we also propose a heuristic approach for the inference of simplices. Experimental results on synthetic and real-world datasets...
Time-variant reliability-based prediction of COVID-19 spread using extended SEIVR model and Monte Carlo sampling
, Article Results in Physics ; Volume 26 , 2021 ; 22113797 (ISSN) ; Mahsuli, M ; Sioofy Khoojine, A ; Hosseini, V. R ; Sharif University of Technology
Elsevier B.V
2021
Abstract
A probabilistic method is proposed in this study to predict the spreading profile of the coronavirus disease 2019 (COVID-19) in the United State (US) via time-variant reliability analysis. To this end, an extended susceptible-exposed-infected-vaccinated-recovered (SEIVR) epidemic model is first established deterministically, considering the quarantine and vaccination effects, and then applied to the available COVID-19 data from US. Afterwards, the prediction results are described as a time-series of the number of people infected, recovered, and dead. Upon introducing the extended SEIVR model into a limit-state function and defining the model parameters including transmission, recovery, and...
A new architecture for analog sampled-data neural filters
, Article IEEE International Symposium on Circuits and Systems 2005, ISCAS 2005, Kobe, 23 May 2005 through 26 May 2005 ; 2005 , Pages 2494-2497 ; 02714310 (ISSN) ; Analui, B ; Sharif Bakhtiar, M ; Sharif University of Technology
2005
Abstract
A new architecture for analog sampled-data filters is presented. This architecture is based on implementing the difference equation of the filter using a neural network. It results in lower sensitivity of filter coefficients to hardware nonidealities. Different tradeoffs in the hardware implementation of the filter are discussed. A design example is also presented. © 2005 IEEE
A hybrid approach for refreshing web page repositories
, Article 10th International Conference on Database Systems for Advanced Applications, DASFAA 2005, Beijing, 17 April 2005 through 20 April 2005 ; Volume 3453 , 2005 , Pages 588-593 ; 03029743 (ISSN) ; Hassanzadeh, O ; Kamali, Sh ; Monemizadeh, M ; Sharif University of Technology
Springer Verlag
2005
Abstract
Web pages change frequently and thus crawlers have to down-load them often. Various policies have been proposed for refreshing local copies of web pages. In this paper, we introduce a new sampling method that excels over other change detection methods in experiment. Change Frequency (CF) is a method that predicts the change frequency of the pages and, in the long run, achieves an optimal efficiency in comparison with the sampling method. Here, we propose a new hybrid method that is a combination of our new sampling approach and CF and show how our hybrid method improves the efficiency of change detection. © Springer-Verlag Berlin Heidelberg 2005