Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99


Any time

2020 ( 2 )

2019 ( 200 )

2018 ( 275 )

2017 ( 293 )

Custom range...

Search Results: 1 - 10 of 224362 matches for " R. Rezaei "
All listed articles are free for downloading (OA Articles)
Page 1 /224362
Display every page Item
A 0.4 V Bulk-Driven Amplifier for Low-Power Data Converter Applications  [PDF]
R. Rezaei, A. Ahmadpour, M. N. Moghaddasi
Circuits and Systems (CS) , 2013, DOI: 10.4236/cs.2013.41016

This paper presents the design of an ultra low-voltage (ULV) pseudo operational transconductance amplifier (P-OTA) that is able to operate with a single supply voltage as low as 0.4 V. The proposed circuit is based on the bulk-driven technique and use of cross-coupled self-cascode pairs that boosts the differential DC gain. The stability condition of this structure for the DC gain is considered by definition of two coefficients to cancel out a controllable percentage of the denominator. This expression for stability condition yield optimized value for the DC gain. Also, as the principle of operation of the proposed technique relies on matching conditions, Monte Carlo analyzes are considered to study of the behavior of the proposed circuit against mismatches. The designed P-OTA have a DC gain of 64 dB, 212 KHz unity gain bandwidth, 57\"\"phase margin that is loaded by 10 pF differential capacitive loads, while consume only 16 μW. Eventually, from the proposed P-OTA, a low-power Sample and Hold (S/H) circuit with sampling frequency of 10 KS/s has been designed and simulated. The correct functionality for this configuration is verified from –30 to 70. The simulated data presented is obtained using the HSPICE Environment and is valid for the 90 nm triple-well CMOS process.

An Efficient Initialization Method for Nonnegative Matrix Factorization
M. Rezaei,R. Boostani,M. Rezaei
Journal of Applied Sciences , 2011,
Abstract: Although Non-negative Matrix Factorization (NMF) has been employed in many real applications but it still suffers from three shortcomings in terms of finding a suitable initialization method, choosing an effective cost function in addition with determining the suitable reduced dimension (Factors Rank). The aim of this study is to enhance NMF performance using Fuzzy C-Means Clustering (FCM) as an efficient initialization method for estimating initial factors of NMF. In this paper, we proposed an initialization in which both W and H matrices are identified simultaneously. The proposed method was applied to JAFFE facial expression dataset and the results exhibited superiority of this method compare to other the state-of-art initialization methods on the employed dataset.
The frequency of urinary stress incontinence after delivery in primiparous women and the related factors
Behdani R,Rezaei E
Tehran University Medical Journal , 2001,
Abstract: In order to determine the frequency rate of urinary stress incontinence (S.I) after delivery and related factors a longitudinal study carried on primiparous women in Arash Hospital in 1379. Through a non probability sampling, 400 eligible women were recruited from available population. Patient with complain of urinary stress incontinence on third day after delivery, were examined and undergone for required diagnostic tests. After stabilizing the diagnosis of urinary stress incontinence, they were followed on 6th week, 3th month and the first year after delivery. The mean of maternal age was 23.5±4.3 years and the mean of gestational age was 37.9±2.1 weeks. The vaginal delivery and cesarean section rates were 83.7 percent and 16.3 percent respectively. From the cases, 50 women (12.5 percent) had S.I on third day after delivery, which 28 of them had this problem from their pregnancy (grup A), and in 22 patients (5.5 percent), S.I were began after delivery (group B). On first year after delivery, only 6 patients (1.5 percent) had complaint of S.I, totally. All patients with S.I had a vaginal delivery and no cases of S.I had found in cesarean section group (65 women). This difference was significant (P=0.019). Comparison of 3 groups A, B and C (including 285 women without S.I after vaginal delivery) had represented that the mean of maternal age and gestational age were significantly higher in group B than other two groups (P=0.0001 and P=0.0009 respectively).
Spectroscopy at the solar limb: I. Average off-limb profiles and Doppler shifts of Ca II H
C. Beck,R. Rezaei
Physics , 2011, DOI: 10.1051/0004-6361/201014976
Abstract: We present constraints on the structure of the chromosphere from observations of the Ca II H line profile near and off the solar limb. We obtained a data set of the Ca II H line in a field of view extending 20" across the limb. We analyzed the spectra for the properties of off-limb spectra. We used tracers of the Doppler shifts, such as the location of the absorption core, the ratio of the two emission peaks H2V and H2R, and intensity images at a fixed wavelength. The average off-limb profiles show a smooth variation with increasing limb distance. The line width increases up to a height of about 2 Mm above the limb. The profile shape is fairly symmetric with nearly identical H2V and H2R intensities; at a height of 5 Mm, it changes into a single Gaussian without emission peaks. We find that all off-limb spectra show large Doppler shifts that fluctuate on the smallest resolved spatial scales. The variation is more prominent in cuts parallel to the solar limb than on those perpendicular to it. As far as individual structures can be unequivocally identified at our spatial resolution, we find a specific relation between intensity enhancements and Doppler shifts: elongated brightenings are often flanked all along their extension by velocities in opposite directions. The average off-limb spectra of Ca II H present a good opportunity to test static chromospheric atmosphere models because they lack the photospheric contribution that is present in disk-center spectra. We suggest that the observed relation between intensity enhancements and Doppler shifts could be caused by waves propagating along the surfaces of flux tubes: an intrinsic twist of the flux tubes or a wave propagation inclined to the tube axis would cause a helical shape of the Doppler excursion, visible as opposite velocity at the sides of the flux tube.
Chromospheric multi-wavelength observations near the solar limb
C. Beck,R. Rezaei
Physics , 2012,
Abstract: Observations of chromospheric spectral lines near and beyond the solar limb provide information on the solar chromosphere without any photospheric contamination. For ground-based observations near and off the limb with real-time image correction by adaptive optics (AO), some technical requirements have to be met, such as an AO lock point that is independent of the location of the field of view observed by the science instruments, both for 1D and 2D instruments. We show how to obtain simultaneous AO-corrected spectra in Ca II H, Ha, Ca II IR at 854 nm, and He I at 1083 nm with the instrumentation at the German Vacuum Tower Telescope in Izana, Tenerife. We determined the spectral properties of an active-region macrospicule inside the field of view in the four chromospheric lines, including its signature in polarization in He I at 1083 nm. Compared to the line-core intensities, the Doppler shifts of the lines change on a smaller spatial scale in the direction parallel to the limb, suggesting the presence of coherent rotating structures or the passage of upwards propagating helical waves on the surfaces of expanding flux tubes.
Recent Advances in the Exploration of the Small-Scale Structure of the Quiet Solar Atmosphere: Vortex Flows, the Horizontal Magnetic Field, and the Stokes-V Line-Ratio Method
O. Steiner,R. Rezaei
Physics , 2012,
Abstract: We review (i) observations and numerical simulations of vortical flows in the solar atmosphere and (ii) measurements of the horizontal magnetic field in quiet Sun regions. First, we discuss various manifestations of vortical flows and emphasize the role of magnetic fields in mediating swirling motion created near the solar surface to the higher layers of the photosphere and to the chromosphere. We reexamine existing simulation runs of solar surface magnetoconvection with regard to vortical flows and compare to previously obtained results. Second, we review contradictory results and problems associated with measuring the angular distribution of the magnetic field in quiet Sun regions. Furthermore, we review the Stokes-V-amplitude ratio method for the lines Fe I 630.15 and 630.25 nm. We come to the conclusion that the recently discovered two distinct populations in scatter plots of this ratio must not bee interpreted in terms of 'uncollapsed' and 'collapsed' fields but they stem from weak granular magnetic fields and weak canopy fields located at the boundaries between granules and the intergranular space. Based on new simulation runs, we reaffirm earlier findings of a predominance of the horizontal field components over the vertical one, particularly in the upper photosphere and at the base of the chromosphere.
R. Rezaei Kalantary, A. Badkoubi
Iranian Journal of Environmental Health Science & Engineering , 2006,
Abstract: Polycyclic Aromatic Hydrocarbons (PAHs) which are introduced into environment are potentially carcinogenic, mutagenic and toxic contaminants. The effect of extractable humic substances (EHS) on bacterial density in bioremediation of anthracene in liquid systems was investigated. The ratio of EHS to anthracene were in two concentrations of 0.35 and 1.05 g dry EHS (with 30% organic matter) per one mg anthracene. In the tests with EHS, an increase in bacterial density even by 8 fold of magnitude was seen in 12-15 days. Then a fast decrease was occurred and prolonged till the end of the test time for the tests that had EHS without anthracene. In the tests which anthracene was the only substrate increasing in bacterial population was not seen. The results showed that up to 21 days the system was free from degradation. So the first increasing in bacterial population showed that EHS might be used as a readily substrate for PAH degraders. The presence of EHS (fulvic and humic acid) can stimulate bacterial community and activity that caused enhancement in anthracene bioremediation.
Soil and Subsurface Sediment Microzonation Using with Seismic Refraction Tomography for Site Assessment (Case Study: IKIA Airport, Iran)  [PDF]
Khalil Rezaei
Open Journal of Geology (OJG) , 2016, DOI: 10.4236/ojg.2016.63016
Abstract: The site effects relating to the amplification of ground motion under earthquake loading are strongly influenced by both the subsurface soil condition and the geologic structure. In this study, for site characterization at the Imam Khomeini International Airport (IKIA) area in south of Tehran, in-situ seismic refraction tomography were carried out as a part of site investigations project, in addition geologic setting, borehole drilling, ground waters information and measurements. Based on seismic refraction studies, three layers are separable which with increasing in depth the S and P wave velocity is increased and this indicates increasing in compaction of soil and geologic materials. In the second and third separated layers, the zones with low and high seismic shear wave velocity is approximately equal, and northeast and southwest of the airport site has the low velocities, in addition to containing loose soils, highly weathered stones, and low depth to groundwater. In terms of Poisson’s ratio, the most important and key installations of airport site are located in suitable positions. According to Iranian Seismic Code, most of the lands around the airport are in class 2 and 3. It seems that a fault or a discontinuity is passed from northwest to the southeast of the study area. This site, according to geological, subsurface geophysical, and geotechnical boreholes studies, is high risk-earthquake prone.
The magnetic flux of the quiet Sun internetwork as observed with the Tenerife Infrared Polarimeter
C. A. R. Beck,R. Rezaei
Physics , 2009, DOI: 10.1051/0004-6361/200911727
Abstract: Recent observations with the HINODE satellite have found abundant horizontal magnetic fields in the internetwork quiet Sun. We compare the results on the horizontal fields with ground-based observations. We obtained 30 sec-integrated data of quiet Sun on disc centre during a period of very good seeing. The data have a rms noise in polarization of around 2 10^-4 of the continuum intensity. The low noise level allowed for an inversion of the spectra. We compare the inversion results with proxies for the determination of magnetic flux. We confirm the presence of the horizontal fields in the quiet Sun internetwork, with voids of some granules extent of nearly zero linear polarization signal. Voids in the circular polarization signal are only of granular scale. More than 60 % of the surface show polarization signals above four times the rms noise level. We find that the total magnetic flux contained in the more inclined to horizontal fields (gamma > 45 deg) is smaller by a factor of around 2 than that of the less inclined fields. The proxies for flux determination are seen to suffer from a strong influence of the thermodynamic state of the atmosphere. We suggest that the difference of the ratio of horizontal to transversal flux between the ground-based infrared data and the satellite-based visible data is due to the different formation heights of the respective spectral lines. We caution that the true amount of magnetic flux cannot be derived directly from the spectra. For purely horizontal flux, one would need its vertical extension that has to estimated by an explicit modeling with the observed spectra as boundary conditions, or has to be taken from MHD simulations.
Cyanobacteria in Biological Soil Crust of Chadormalu Area, Bafq Region in Central Iran
A. Moghtaderi,M. Taghavi,R. Rezaei
Pakistan Journal of Nutrition , 2009,
Abstract: Arid and semi-arid regions are characterized by sparse vegetation or absence of vegetation cover. The absence of a dense distribution of macrophytes (higher plants), much of arid and semi-arid surfaces are covered by microphytic communities of small non-vascular plants. An important group of organisms comprising soil crusts in such habitats are cyanobacteria. In this research the genus and species of cyanobacteria were detected at the Chadormalu desert, Yazd Province of Iran. The study showed that cyanobacteria (Microcoleous vaginatus, Nostoc.sp, Microcystis.sp, Ocillatoria.sp, Chroococcuss.sp, Chroococcidiopsis, Ocillatoria.sp, Chroococcuss.sp, Microcystis.sp) at Chadormalu Desert are comparable with other Deserts in cold and warm dry conditions.
Page 1 /224362
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.