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Search Results: 1 - 10 of 1192 matches for " Ehsan Abbasi "
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Modeling Accidents on Mashhad Urban Highways  [PDF]
Esmaeel Ayati, Ehsan Abbasi
Open Journal of Safety Science and Technology (OJSST) , 2014, DOI: 10.4236/ojsst.2014.41004
Abstract:


In recent years, numerous researches have been carried out with purpose of predicting motor vehicle crashes on transportation facilities as freeways and urban or rural highways. Accident process can be modeled successfully with assuming a dual-state data-generating process. Based on this assumption, road components like intersections or road segments have two states of perfectly safe and unsafe. Zero-inflated regression models are applied to model accidents usually in cases of preponderance of excess zero data in crash data. We handle in this research, the investigation into effective factors on frequency and severity of accidents on urban highways and use crash data of Mash had-Iran urban highways as a case study. We use in this study, the Poisson, Negative binomial, Zero-inflated Poisson and Zero-inflated Negative binomial regression models for modeling accidents, and traffic flow and road geometry related variables as in dependent variables of models. In addition to identifying effective factors on crash occurrence probability, we deal with comparison of models, evaluate and prove the efficiency of Zero-inflated regression models against traditional Poisson and Negative binomial models.


The LASSO with Non-linear Measurements is Equivalent to One With Linear Measurements
Chrtistos Thrampoulidis,Ehsan Abbasi,Babak Hassibi
Statistics , 2015,
Abstract: Consider estimating an unknown, but structured, signal $x_0\in R^n$ from $m$ measurement $y_i=g_i(a_i^Tx_0)$, where the $a_i$'s are the rows of a known measurement matrix $A$, and, $g$ is a (potentially unknown) nonlinear and random link-function. Such measurement functions could arise in applications where the measurement device has nonlinearities and uncertainties. It could also arise by design, e.g., $g_i(x)=\text{sign}(x+z_i)$, corresponds to noisy 1-bit quantized measurements. Motivated by the classical work of Brillinger, and more recent work of Plan and Vershynin, we estimate $x_0$ via solving the Generalized-LASSO for some regularization parameter $\lambda>0$ and some (typically non-smooth) convex structure-inducing regularizer function. While this approach seems to naively ignore the nonlinear function $g$, both Brillinger (in the non-constrained case) and Plan and Vershynin have shown that, when the entries of $A$ are iid standard normal, this is a good estimator of $x_0$ up to a constant of proportionality $\mu$, which only depends on $g$. In this work, we considerably strengthen these results by obtaining explicit expressions for the squared error, for the \emph{regularized} LASSO, that are asymptotically \emph{precise} when $m$ and $n$ grow large. A main result is that the estimation performance of the Generalized LASSO with non-linear measurements is \emph{asymptotically the same} as one whose measurements are linear $y_i=\mu a_i^Tx_0 + \sigma z_i$, with $\mu = E\gamma g(\gamma)$ and $\sigma^2 = E(g(\gamma)-\mu\gamma)^2$, and, $\gamma$ standard normal. To the best of our knowledge, the derived expressions on the estimation performance are the first-known precise results in this context. One interesting consequence of our result is that the optimal quantizer of the measurements that minimizes the estimation error of the LASSO is the celebrated Lloyd-Max quantizer.
BER Analysis of the box relaxation for BPSK Signal Recovery
Christos Thrampoulidis,Ehsan Abbasi,Weiyu Xu,Babak Hassibi
Mathematics , 2015,
Abstract: We study the problem of recovering an $n$-dimensional vector of $\{\pm1\}^n$ (BPSK) signals from $m$ noise corrupted measurements $\mathbf{y}=\mathbf{A}\mathbf{x}_0+\mathbf{z}$. In particular, we consider the box relaxation method which relaxes the discrete set $\{\pm1\}^n$ to the convex set $[-1,1]^n$ to obtain a convex optimization algorithm followed by hard thresholding. When the noise $\mathbf{z}$ and measurement matrix $\mathbf{A}$ have iid standard normal entries, we obtain an exact expression for the bit-wise probability of error $P_e$ in the limit of $n$ and $m$ growing and $\frac{m}{n}$ fixed. At high SNR our result shows that the $P_e$ of box relaxation is within 3dB of the matched filter bound MFB for square systems, and that it approaches MFB as $m $ grows large compared to $n$. Our results also indicates that as $m,n\rightarrow\infty$, for any fixed set of size $k$, the error events of the corresponding $k$ bits in the box relaxation method are independent.
Critical Incident Reported in an Obstetric Unit of a Tertiary Care Hospital of a Developing Country, over a Period of Two Years  [PDF]
Shemila Abbasi
Open Journal of Obstetrics and Gynecology (OJOG) , 2017, DOI: 10.4236/ojog.2017.712125
Abstract: Introduction: A lot of literature is available on critical incidents and near misses but specialty based critical incidents are very scanty. Aim: In this audit, we aimed to report critical incident and near misses during conduct of obstetric anesthesia over a period of two years. Methodology: Critical incident forms were collected, entered, analyzed and categorized on the basis of American Standards Association (ASA), phase of incidents, system involved, and type of errors, outcome and action taken. Human error was further categorized on the basis of their contributing factor marked in form. Results: During the reporting period, 5511 anaesthetics were administered and 55 reports were received out of which 53 reports were included in analysis. Fifty three reports were divided into 33 critical incidents and 20 near misses. Out of 33 critical incidents, 54.5% involved CVS system and musculoskeletal system, followed by neuromuscular (n = 5), drug related (n = 4), airway/respiratory system (n = 2), central nervous system (n = 2) and renal system (n = 1). Forty five incidents possess no untoward effect while 7 led to minor and only one to severe physiological disturbance. Human errors were (n = 30) 57% reports and failure to check was the main contributory factor. Conclusion: Critical incidents reporting needs to be introduced in sub-specialties at departmental, national and international level. Checking of equipment, medication and anesthesia machine must be part of regular checks in elective and emergency cases.
Adaptive Wavelet Filtering for Data Enhancement in Wireless Sensor Networks  [PDF]
Ehsan Sheybani
Journal of Sensor Technology (JST) , 2012, DOI: 10.4236/jst.2012.22012
Abstract: Noise (from different sources), data dimension, and fading can have dramatic effects on the performance of wireless sensor networks and the decisions made at the fusion center. Any of these parameters alone or their combined result can affect the final outcome of a wireless sensor network. As such, total elimination of these parameters could also be damaging to the final outcome, as it may result in removing useful information that can benefit the decision making process. Several efforts have been made to find the optimal balance between which parameters, where, and how to remove them. For the most part, experts in the field agree that it is more beneficial to remove noise and/or compress data at the node level. We have developed computationally low power, low bandwidth, and low cost filters that will remove the noise and compress the data so that a decision can be made at the node level. This wavelet-based method is guaranteed to converge to a stationary point for both uncorrelated and correlated sensor data. This is mainly stressed so that the low power, low bandwidth, and low computational overhead of the wireless sensor network node constraints are met while fused datasets can still be used to make reliable decisions.
Real-Time Internet-Based Teleoperation  [PDF]
Ehsan Kamrani
Intelligent Control and Automation (ICA) , 2012, DOI: 10.4236/ica.2012.34041
Abstract: Internet-based teleoperation employs robots and internet a two breakthrough technologies to manipulate robots from distance for different applications. Variable and unknown time delay dynamics of internet is the main obstacle for realtime teleoperation via internet. In this paper the internet delay dynamics and its characteristics have been studied based on the measurement in different nodes. Then a black-box model for end-to-end internet delay dynamics has been developed using system identification and Auto-Regressive eXogeneous (ARX) model. Our experimental studies show a regular periodic behaviour in long-term intervals of internet delay variation and also confirm the accuracy and reliability of our theoretical and modelling derivations. This paper also introduces a novel multivariable control method for real-time telerobotic operations via Internet. Random communications delay of the Internet can cause instability in realtime closed-loop telerobotic systems. When a single identification model is used, it will have to adapt itself to the operating condition before an appropriate control mechanism can be applied. Slow adaptation may result in a large transient error. As an alternative, we propose to use a Multiple Model framework. The control strategy is to determine the best model for the current operating condition and activate the corresponding controller. We propose the use of Multi-Model Adaptive Control Theory and Multivariable Wave prediction method to capture the concurrency and complexity of Internet-based teleoperation. The results confirm the efficiency of the proposed technique in dealing with constant and variable delay dynamics of internet.
Adsorption of Cerium (IV) from Aqueous Solutions Using Activated Carbon Developed from Rice Straw  [PDF]
Ehsan Farahmand
Open Journal of Geology (OJG) , 2016, DOI: 10.4236/ojg.2016.63017
Abstract: In this study, the adsorption of Cerium from synthetic solution containing cerium oxide is investigated using activated carbon developed from rice straw that is activated by H3PO4. SEM and FTIR techniques are used to examine structural and morphological characteristics of rice straw and activated carbon. The optimum conditions obtained with the highest adsorption include contact time = 500 minutes, pH = 4, temperature = 35°C, cerium concentration = 300 ppm, and adsorbent dosage = 0.02 gr. The highest adsorption of Cerium is determined by 4.13 mg/g. Adsorption kinetics of cerium and equilibrium behavior is studied. It indicates that the adsorption process obeys Pseudo-first-order kinetic model and Langmuir isotherm model. The results of this study show that the activated carbon developed from rice straw activated by H3PO4 is a relatively effective adsorbent for the adsorption of cerium from aqueous solution.
BEAR: A Balanced Energy-Aware Routing Protocol for Wireless Sensor Networks  [PDF]
Ehsan Ahvar, Mahmood Fathy
Wireless Sensor Network (WSN) , 2010, DOI: 10.4236/wsn.2010.210095
Abstract: Energy aware routing protocols can be classified into energy saver and energy manager. Energy saver protocols decrease energy consumption totally. Most of them try to find the shortest path between source and destination to reduce energy consumption. But energy manager protocols balance energy consumption in network to avoid network partitioning. Finding best route only based on energy balancing consideration may lead to long path with high delay and decreases network lifetime. On the other hand, finding best route only with the shortest distance consideration may lead to network partitioning. This paper improves SEER [1] routing protocol. Traditional SEER is only energy saver and has poor idea about energy balancing. Our proposed protocol, named BEAR, considers energy balancing and optimal distance both. It finds a fair tradeoff between energy balancing and optimal distance by learning automata concept. We simulate and evaluate routing protocols by Glomosim [2] simulator.
Using Extended Finite Element Method for Computation of the Stress Intensity Factor, Crack Growth Simulation and Predicting Fatigue Crack Growth in a Slant-Cracked Plate of 6061-T651 Aluminum  [PDF]
Ehsan Hedayati, Mohammad Vahedi
World Journal of Mechanics (WJM) , 2014, DOI: 10.4236/wjm.2014.41003
Abstract:

The 6061-T651 aluminium alloy is one of the most common aluminium alloys for marine components and general structures. The stress intensity factor (SIF) is an important parameter for estimating the life of the cracked structure. In this paper, the stress intensity factors of a slant-cracked plate, which is made of 6061-T651 aluminum, have been calculated using extended finite element method (XFEM) and finite element method (FEM) in ABAQUS software and the results were compared with theoretical values. Numerical values obtained from these two methods were close to the theoretical values. In simulations of crack growth at different crack angles, the crack propagation angle values were closer to the theoretical values in XFEM method. Also, the accuracy and validity of fatigue crack growth curve were much closer to the theoretical graph in XFEM than the FEM. Therefore, in this paper the capabilities of XFEM were realized in analyzing issues such as cracks.

Study on the Effects of Work Teams on Human Resources Excellence  [PDF]
Ebrahim Kalani, Ehsan Kamrani
Journal of Human Resource and Sustainability Studies (JHRSS) , 2017, DOI: 10.4236/jhrss.2017.51002
Abstract: The conception and use of work teams have been one of the main subjects of management researches for the last few decades and in the past years many developments have happened in the kinds and usage of them, which have improved the condition of organizations and human resources management. Our objective in this paper is to observe the formation of work teams and how they affect human resources excellence. Finding new and creative solutions for todays intricate situations is becoming more and more difficult and employees can’t solve them on their own anymore and this shows and bolds the importance of teamwork and forming work teams. The main objective however in this paper is to evaluate the effect of 5 main characteristics of work teams (which are team structure, leadership, control, mutual support and communication) on the 3 main characteristics of human resources excellence (which are delegation, motivation and team work) in Torang Darya Shipping Company. To do so, 200 personnel at the department were randomly selected from 450 personnel by Cochran sample size formula and answered to the research made questionnaire derived from[1][2] and[3]. The content validity of the questionnaire has been confirmed by the experts and academicians and the reliability has also been confirmed
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