samad abbaszadeh - Academia.edu (original) (raw)

Papers by samad abbaszadeh

Geotechnical and Structural Engineering Congress 2016, 2016

Significant effort has been placed on the determination of swelling properties of expansive soils... more Significant effort has been placed on the determination of swelling properties of expansive soils, such as swell pressure and swell potential. However, there are only a limited number of studies of expansive soil response that include the effect of desiccation cracking; most studies and methods of analysis have simply neglected the effect of cracks. At the same time that cracks provide a path for flow of water under positive head, the crack network in an expansive soil functions as swell-absorbent media (due to open spaces within the soil) which can reduce the total amount of vertical swell that the soil would experience. In this study, a laboratory investigation was carried out to quantitatively evaluate the effect of cracks on swell potential and swelling pressure. The presence of desiccation cracks was found to reduce the amount of swell and also reduce the swell pressure compared to intact, uncracked, specimens. The percentage reduction of swell potential and swell pressure was found to be a function of the volume of cracks and the applied net normal stress.

ABSTRACT In order to improve the performance of amorphous selenium (a-Se) based detectors, it is ... more ABSTRACT In order to improve the performance of amorphous selenium (a-Se) based detectors, it is beneficial to operate the device at high electric field (≥10 V/μm). Increasing the electric field reduces the ionization energy and increases the hole mobility within the a-Se detector. In order for a practical a-Se detector to be capable of working at a high electric field, injection of holes from the positively biased electrode and injection of electrons from the negatively biased electrode should be prevented. We have investigated different organic materials with high ionization potential as hole-blocking contacts for a-Se based photodetectors. The effect of the organic layer thickness on the dark current and photocurrent performance of the detector was examined. It was found that the injection of holes could be reduced at high electric fields by increasing the thickness of the organic layer.

ABSTRACT We investigate the stability against photo-induced crystallization (PiC) and photo-induc... more ABSTRACT We investigate the stability against photo-induced crystallization (PiC) and photo-induced darkening (PiD) in a series of amorphous selenium (a-Se) films grown with and without polyimide buffer layers[1] for temperatures below and above the glass transition (Tg ∼ 313 K). The a-Se films are bulk-like (∼16.5 μm thick), and contain a low concentration of As (< 0.2%). We find that due to strain relief, a thin layer (∼1 μm) of polyimide greatly stabilizes the samples against PiC and reduces the effect of PiD.

IEEE Transactions on Electron Devices, 2014

ABSTRACT We examined the potential application of indium gallium zinc oxide (IGZO) as a hole-bloc... more ABSTRACT We examined the potential application of indium gallium zinc oxide (IGZO) as a hole-blocking layer for an amorphous selenium (a-Se)-based detector to reduce the dark current and improve the sensitivity of the detector. By employing a thin layer of IGZO (375 nm), the dark current of an a-Se detector remains below 1 pA/mm (^{2}) up to electric fields as high as 60 V/ (mu ) m. The measured dark current at different electric fields is comparable to the thermal generation currents in a-Se, thus demonstrating the good hole-blocking properties of IGZO. The detector’s photo response was characterized using a blue light-emitting diode at different electric fields. A factor of three improvement in external quantum efficiency was observed by increasing the electric field of the detector from 10 to 50 V/ (mu ) m.

ABSTRACT Traditionally, samples are collected on-site (i.e., in the field) and are shipped to a l... more ABSTRACT Traditionally, samples are collected on-site (i.e., in the field) and are shipped to a lab for chemical analysis. An alternative is offered by using portable chemical analysis instruments that can be used on-site (i.e., in the field). Many analytical measurements by optical emission spectrometry require use of light-sources and of spectral lines that are in the Ultra-Violet (UV, ~200 nm – 400 nm wavelength) region of the spectrum. For such measurements, a portable, battery-operated, fiber-optic spectrometer equipped with an un-cooled, linear, solid-state detector may be used. To take full advantage of the advanced measurement capabilities offered by state-of-the-art solid-state detectors, cooling of the detector is required. But cooling and other thermal management hamper portability and use on-site because they add size and weight and they increase electrical power requirements. To address these considerations, an alternative was implemented, as described here. Specifically, a microfabricated solid-state detector for measurement of UV photons will be described. Unlike solid-state detectors developed on crystalline Silicon, this miniaturized and low-cost detector utilizes amorphous Selenium (a-Se) as its photosensitive material. Due to its low dark current, this detector does not require cooling, thus it is better suited for portable use and for chemical measurements on-site. In this paper, a microplasma will be used as a light-source of UV photons for the a-Se detector. For example, spectra acquired using a microplasma as a light-source will be compared with those obtained with a portable, fiber-optic spectrometer equipped with a Si-based 2080-element detector. And, analytical performance obtained by introducing ng-amounts of analytes into the microplasma will be described.

SPIE Proceedings, 2012

ABSTRACT Several strategies have been investigated to acquire both low- and high-energy images si... more ABSTRACT Several strategies have been investigated to acquire both low- and high-energy images simultaneously for contrastenhanced mammography (CEM). However, for the dual-energy technique where the existing conventional mammography infrastructure can be leveraged, low- and high-energy images are acquired using two separate exposures and the finite time between image acquisition leads to motion artifacts in the combined image. Motion artifacts lead to greater noise in the combined image and affect image quality, however the relationship between them is not clear. In this study we examine motion artifacts in dual-energy CEM and their impact on anatomical noise in the combined image and tumor detectability. To study the impact of motion artifacts, a cascaded systems model is extended to include such motion artifacts. An ideal observer model is used to quantify the performance and CEM images from a previous clinical study are used for comparison of the extended model.

IEEE Sensors Journal, 2015

ABSTRACT Cerium oxide has proven as a proper hole-blocking contact in multilayer amorphous seleni... more ABSTRACT Cerium oxide has proven as a proper hole-blocking contact in multilayer amorphous selenium X-ray detectors to reduce leakage current by limiting hole injection. To further improve its blocking properties, one of the key factors is to prepare a thin layer of cerium oxide with full oxidation. In this paper, a cerium oxide thin film was deposited by reactive oxygen ion assisted e-beam evaporation that utilized an independent oxygen ion source to create ionized oxygen, allowing for a refined oxidation control without requiring high process temperatures. Compared with films obtained without ion-beam assistance, oxygen ion assisted deposition enhanced the refractive index of oxide film from ~1.8 to 2.2 at a wavelength of 550 nm and improved the electrical resistivity from ~106 to 1010 Qcm. X-ray photoelectron spectroscopy and X-ray diffraction measurements further gave insights into the stoichiometry and the crystal structures. To investigate blocking effectiveness, multilayer selenium sandwich structures with and without the cerium oxide blocking contact were fabricated and the leakage current was evaluated.

Journal de Mycologie Médicale / Journal of Medical Mycology, 2014

Key Engineering Materials, 2013

In this paper, a thin layer of perylene tetracarboxylic bisbenzimidazole (PTCBI) is investigated ... more In this paper, a thin layer of perylene tetracarboxylic bisbenzimidazole (PTCBI) is investigated as a potential hole-blocking contact in an a-Se photodetector. The behavior of the device was characterized as a function of electric field under light and dark conditions. It was found that the PTCBI layer permits operation at high electric fields (>>10 V/μm) while maintaining a dark current density below 200 pA/mm2. Short pulse experiments were performed to assure that charge accumulation at the organic/a-Se interface is negligible and does not reduce the electric field in the a-Se layer. The detector investigated uses a simple low temperature fabrication process based on widely available semiconductor materials that can be easily integrated into current large area digital imager manufacturing processes.

Nephro-Urology …, 2009

... Behzad Einollahi Nephrology and Urology Research Center, Baqiyatallah University of Medical S... more ... Behzad Einollahi Nephrology and Urology Research Center, Baqiyatallah University of Medical Sciences, Tehran, Iran: Correspondence: Shahin Abbaszadeh MD. ... On the contrary, Osman et al. reported unfavorable results (21). ...

Physics in Medicine and Biology, 2012

In contrast-enhanced mammography (CEM), the dual-energy dual-exposure technique, which can levera... more In contrast-enhanced mammography (CEM), the dual-energy dual-exposure technique, which can leverage existing conventional mammography infrastructure, relies on acquiring the low- and high-energy images using two separate exposures. The finite time between image acquisition leads to motion artifacts in the combined image. Motion artifacts can lead to greater anatomical noise in the combined image due to increased mismatch of the background tissue in the images to be combined, however the impact has not yet been quantified. In this study we investigate a method to include motion artifacts in the dual-energy noise and performance analysis. The motion artifacts are included via an extended cascaded systems model. To validate the model, noise power spectra of a previous dual-energy clinical study are compared to that of the model. The ideal observer detectability is used to quantify the effect of motion artifacts on tumor detectability. It was found that the detectability can be significantly degraded when motion is present (e.g., detectability of 2.5 mm radius tumor decreased by approximately a factor of 2 for translation motion on the order of 1000 μm). The method presented may be used for a more comprehensive theoretical noise and performance analysis and fairer theoretical performance comparison between dual-exposure techniques, where motion artifacts are present, and single-exposure techniques, where low- and high-energy images are acquired simultaneously and motion artifacts are absent.

Physics in Medicine and Biology, 2011

Medical Physics, 2013

The authors describe modifications to previously developed cascaded systems analysis to include t... more The authors describe modifications to previously developed cascaded systems analysis to include the anatomical noise in evaluation of dual-energy noise reduction techniques. Previous models have ignored the anatomical noise in theoretical analysis of noise reduction techniques. The inclusion of anatomical noise leads to more accurate estimation of potential noise reduction improvements and optimization. The model is applied to dual-energy contrast-enhanced mammography. The effect of linear noise reduction filters on the anatomical noise is taken into account using cascaded systems analysis. The noise model is included in the ideal observer detectability for performance evaluation of the noise reduction techniques. Dual-energy image noise with and without including the effect of anatomical noise in noise reduction technique analysis is reported. The theoretical model is compared with clinical images from a previous dual-energy contrast enhanced mammography clinical study and good agreement is observed. The results suggest that the inclusion of anatomical noise in the evaluation and comparison of noise reduction techniques is highly warranted for more accurate analysis. This work establishes a useful extension to dual-energy cascaded systems analysis for maximizing image quality using noise reduction techniques. The extension includes the effect of linear image filtering, such as that used for noise reduction, on anatomical noise. The results suggest that the inclusion of anatomical noise in the evaluation of noise reduction techniques can lead to more accurate optimization, noise, and performance estimations.

Journal of Non-Crystalline Solids, 2012

ABSTRACT The photodarkening (PD) effect has been studied experimentally for amorphous selenium (a... more ABSTRACT The photodarkening (PD) effect has been studied experimentally for amorphous selenium (a-Se) layers with 0.2 wt.% of arsenic (As) deposited on different substrates: glass, indium tin oxide (ITO) coated glass and polyimide-coated ITO glass. It was found that the presence of As qualitatively affects the behavior of PD: while in pure (no As) a-Se the relaxation of the PD is a fast process characterized by a short (~ 10 s) time constant, in As-containing a-Se it has both short (same as in pure a-Se) and comparably long (~ 80 s) components. The interface between a-Se and the substrate affects the PD qualitatively: it influences the magnitude of the effect while not changing the kinetics of the process. The buildup of the PD was more pronounced for the glass substrate (the most rigid) and was least pronounced for the polyimide-coated ITO glass (the most flexible). The difference can be attributed to a different strain at the interface.

Journal of Inequalities and Applications, 2009

Journal of Cleaner Production, 2014

ABSTRACT Traditionally chemical process design has been built on the primary basis of economic vi... more ABSTRACT Traditionally chemical process design has been built on the primary basis of economic viability. However with the growing concern on sustainability, the design of petrochemical plant can no longer be focused only on the techno-economic criteria. As for the environmental performance of a petrochemical process, to date the approach for environmental solutions for process facilities are mostly revolved around the concept of end-of-pipe pollution control techniques, aiming to attain waste treatment, toxicity diminution and industrial discharge volume reduction. This however is not a cost-effectiveness and sustainable approach since hazards do still present in the process, making the process inherently less environmental friendlier in the first place. This paper compared eighteen existing methods for assessing environmental friendliness of a process early starting from the design stage. The comparison of the environmental assessment methods as presented here shows that the diversity of the methods has a good balance between simplicity and complexity, depending on the aim of the particular method itself. It is found that achieving a comprehensive yet simple method is actually possible, by developing such method exclusively for specific stage of the design phase and not claiming to be applicable throughout the whole design phase, as what most of the previous works did. The review conducted in this work suggests that a deeper study associated with an assessment of petrochemical processes' environmental impact in specific stages of process design is highly needed.