S. Fayek - Academia.edu (original) (raw)

Papers by S. Fayek

Journal of Alloys and Compounds, 2008

The radial distribution function (RDF) of As 30 Se 70−x Sn x amorphous films was obtained by X-ra... more The radial distribution function (RDF) of As 30 Se 70−x Sn x amorphous films was obtained by X-ray diffraction. Depending on the composition and preparing conditions, the short-range order of the melt-quenched, and thermally evaporated As 30 Se 70−x Sn x (x = 0, 3 at.%) is described. Structural parameters such as interatomic distances and bond angles were derived and proposed as a good statistical description of the glasses under study. Both the disorder network structure of the glass matrix and the transport properties have been studied according to the chemical properties of Sn as a doping element. The activation energies calculated from dc conductivity is obtained. The effect of composition and average coordination number N c on the number of topological constraints N con , the number of lone-pair electrons L, the mean atomic volume V a and the glass transition temperature T g have been studied, in the light of recent model proposed for covalent random network. The occurrence of this dependence leads to the conclusion that Sn has a marked effect on the electronic state of the host glass.

Materials Science and Engineering: A, 2014

Effects of γ-irradiation and deformation temperatures on the hardening behavior of Al-5356 alloy ... more Effects of γ-irradiation and deformation temperatures on the hardening behavior of Al-5356 alloy have been investigated by means of stress–strain measurements. Wire samples irradiated with different doses (ranging from 500 to 2000 kGy) were strained at different deformation temperatures T w (ranging from 303 to 523 K) and a constant strain rate of 1.5 Â 10 À 3 s À 1. The effect of γ-irradiation on the work-hardening parameters (WHP): yield stress s y , fracture stress s f , total strain ε T and work-hardening coefficient χ p of the given alloy was studied at the applied deformation temperature range. The obtained results showed that γ-irradiation exhibited an increase in the WHP of the given alloy while the increase in its deformation temperature showed a reverse effect. The mean activation energy of the deformation process was calculated using an Arrhenius-type relation, and was found to be $ 80 kJ/mole, which is close to that of grain boundary diffusion in aluminum alloys.

Bulletin of Materials Science, 2014

Optical properties and conductivity of glassy (As 2 Se 3 ) 3−x (As 2 Te 3 ) x were studied for 0 ... more Optical properties and conductivity of glassy (As 2 Se 3 ) 3−x (As 2 Te 3 ) x were studied for 0 ≤ x ≤ 3. The films of the above mentioned compound were prepared by thermal evaporation with thickness of about 250 nm. The optical-absorption edge is described and calculated using the non-direct transition model and the optical band gap is found to be in the range of 0.92 to 1.84 eV. While, the width of the band gap tail exhibits opposite behaviour and is found to be in the range of 0.157 to 0.061 eV, this behaviour is believed to be associated with cohesive energy and average coordination number. The conductivity measurement on the thin films is reported in the temperature range from 280 to 190 K. The conduction that occurs in this low-temperature range is due to variable range hopping in the band tails of localized states, which is in reasonable agreement with Mott's condition of variable range hopping conduction. Some parameters such as coordination number, molar volume and theoretical glass transition temperature were calculated and discussed in the light of the topological bonding structure.

Transplantation Proceedings, 2015

Background. Prophylaxis against hepatitis B virus (HBV) recurrence after orthotopic liver transpl... more Background. Prophylaxis against hepatitis B virus (HBV) recurrence after orthotopic liver transplantation (OLT) includes lifelong hepatitis B immunoglobulin (HBIG) and oral antiviral agent(s). In the presence of high-genetic-barrier nucleos(t)ide analogues, the need for lifelong HBIG is questioned. We evaluated the safety and cost-effectiveness of a limited HBIG course. Methods. OLT from 2006 to 2013 were reviewed. Patients with pre-OLT hepatitis B virus surface antigen who received HBV prophylaxis with 2 HBIG doses (anhepatic and first post-operative day; 10,000 units/dose) and potent nucleos(t)ide analogues were included. The primary end point was HBV recurrence (HBV-DNA detection). Results. Thirteen patients (primary transplants) were included, median Model for End-Stage Liver Disease score was 18, and there was no fulminant failure; HBV-DNA was detected in 4 patients at OLT. After OLT, 10 patients received entecavir and/or tenofovir. Median follow-up was 23 months. One recurrence occurred (7.7%) at month 13 (HBV-DNA: 14 IU/mL); the graft maintained excellent function. This minimal viremic expression is related to hepatocellular carcinoma recurrence with neoplastic replication carrying integrated HBV-DNA; thus, there is no defined HBV viral recurrence. No graft loss or patient death was related to HBV recurrence. The 1-year patient and graft survival rate was 84.6%. Cost-savings in the first year was $178,100 per patient when compared with Food and Drug Administrationeapproved HBIG dosing. Conclusions. In the era of potent oral nucleos(t)ide analogues, a limited HBIG course appears to be cost-effective in preventing HBV recurrence.

Acta Physica Hungarica, 1990

X-ray diffraction studies for sixteen compositions of recrystallized samples for Tl x Se1−x syste... more X-ray diffraction studies for sixteen compositions of recrystallized samples for Tl x Se1−x system, withx=0.0 up tox=0.9, shows the existence of four crystalline phases. Crystalline hexagonal selenium exists in the range ofx=0.0 tox=0.4, which is a glass region boundary, indicating the responsibility of selenium for forming Se−Tl glasses. Tetragonal SeTl crystalline phase exists in the wide range ofx=0.005 tox=0.9, and

Journal of Non-crystalline Solids, 2011

Thermally induced solid state reaction of Ag(Cu) into thin Ge(S x Se 1 − x ) 2 films with x = 0, ... more Thermally induced solid state reaction of Ag(Cu) into thin Ge(S x Se 1 − x ) 2 films with x = 0, 0.1, 0.4 and 1.0 was investigated using a step by step technique in order to design films with exact Ag(Cu) concentrations for applications in integrated IR optical devices. A thin film of Ag(Cu) was deposited on top of the host Ge(S x Se 1 − x ) 2 films followed by annealing in vacuum at constant temperature, which resulted in homogeneous films of good optical quality. The variation in Ag(Cu) concentration in the films ranged between 5 and 35 at.%. The kinetics of the diffusion and dissolution of metal in the host films was measured by optically monitoring the change in thickness of doped chalcogenide during consecutive thermal annealing steps. The kinetics studies revealed that the thermal dissolution rate of the Cu is greater than that of Ag. Optical UV-VIS transmission spectra of chalcogenide glass layers, undoped and thermal doped by Ag(Cu), were measured to establish the optical properties of the films. The spectra were analyzed using the technique proposed by Swanepoel and the results show that the addition of metal increases the absorption coefficient in the power-law regime and consequently the optical gap decreases and the refractive index increases. The amorphous character of the films was checked by X-ray diffraction which confirmed the amorphous structure of all Ag(Cu)\Ge\S\Se thin films.

Vacuum, 1999

Understanding of the effect of the addition of Tl on glassy As2Se3 prepared under vacuum, has gre... more Understanding of the effect of the addition of Tl on glassy As2Se3 prepared under vacuum, has greatly improved with the advent of several structural and chemical models, which predict the influence of such an addition, in terms of the average heat of atomization Hs and the average coordination number Nco. The latter are computed from the atomization and the coordination number of the elements, respectively. A correlation had been found between the chalcogenide system (As2Se3)1−xTlx and the number of lone-pair electrons. The stable vitreous state can be obtained only if enough lone-pair electrons exist in the structure of the chalcogenide system. The cation in the chalcogenide glasses may interact with the lone-pair electrons, of bridging chalcogen atoms and influence the glass forming ability. Investigation of the dependence of the differential thermal analysis (DTA) and, optical gap Eg “previously published” on the composition of vacuum prepared (As2Se3)1−xTlx revealed that the average coordination number Nco, has a great effect on these properties. The nature of the Nco dependencies is discussed in relation to topological and percolative consideration.

Vacuum, 2006

Thin films of Ge 28Àx Se 72 Sb x (x ¼ 0, 8, 16, 24 at%) with thickness of 200 nm are prepared by ... more Thin films of Ge 28Àx Se 72 Sb x (x ¼ 0, 8, 16, 24 at%) with thickness of 200 nm are prepared by thermal evaporation onto glass substrates under vacuum of 5.3 Â 10 À5 mbar. Optical reflectance and transmittance of these films are measured at room temperature in the light wavelength region from 200 to 1100 nm. The estimated optical energy gap, E g , is found to decrease from 2 eV (0 at% Sb) to 1.5 eV (24 at% Sb), whereas the band tail width, E e , increases from 0.062 to 0.077 eV, respectively. The refractive index, n, and extinction coefficient, k, are determined as functions of wavelength. The DC electrical conductivity, s, of films is measured as a function of temperature in the range from 300 to 360 K. The extracted value of activation energy, DE, is found to decrease from 0.95 eV (0 at% Sb) to 0.74 eV (24 at% Sb). Optical and electrical behavior of films can be explained in terms of cohesive energy (CE) and Se-Se defect bonds. r

Transplantation Proceedings, 2007

Candidates for liver transplantation (OLT) may be found to have an incidental extrahepatic tumor,... more Candidates for liver transplantation (OLT) may be found to have an incidental extrahepatic tumor, which is amenable to resection, and may be associated with variable long-term survival. Issues to be considered include: (1) Whether it is possible to define a tumor stage and survival expectancy, which makes the patient an acceptable transplant candidate;

Transplantation Proceedings, 2013

Background. Although the LigaSure device is widely used, its use in liver transplantation, where ... more Background. Although the LigaSure device is widely used, its use in liver transplantation, where compounding factors of portal hypertension, coagulopathy, and thrombocytopenia exist, is poorly described. Methods. From October 1, 2011, to December 31, 2011, 6 patients underwent liver transplantation with recipient hepatectomy utilizing the LigaSure device. Outcomes using the device were compared with 6 contemporaneous patients in whom the device was not used.

Transplantation Journal, 2012

Transplantation Journal, 2010

Surgical Endoscopy, 2007

Intraoperative cholangiography (IOC) during laparoscopic cholecystectomy (LC) is used to assess t... more Intraoperative cholangiography (IOC) during laparoscopic cholecystectomy (LC) is used to assess the anatomy of the biliary tree and to detect any stones contained within it. Intraoperative cholangiography may be performed either routinely or more selectively in cases with high suspicion of choledocholithiasis or for those patients whose anatomy appears unclear at operation 1 . In cases where significant inflammation is present the cystic duct may be short, thickened or dilated and thus difficult to be manipulated to obtain a satisfactory IOC. We describe a safe, simple, reliable technique to control the "difficult" cystic duct during IOC. At Fairview Hospital, Cleveland, Ohio we attempt IOC routinely in all patients undergoing LC. In patients with dilated, thick cystic duct we describe a novel method for controlling the duct with a vascular vessel loop instead of a surgical clip to obtain good control and avoiding extravasation of dye during IOC. The feasibility, safety and results of this technique are described. During a 1 year period, this technique has been used in 10 patients. This technique was successful in all attempted cases. A good quality IOC was obtained from first attempt in all cases. The cystic duct was then occluded in all cases using a Vicryl "0" endoloop. One patient had a common bile duct stone and this patient received a postoperative ERCP. All patients were discharged home with no complications. In cases where a short, thickened or dilated cystic duct is present, ductal control during IOC can be easily obtained using a vascular vessel loop. This is a safe, reliable, less traumatic, readily available and inexpensive method that provides a secure way of handling the "difficult" cystic duct

physica status solidi (a), 2007

The effects of adding transition metals (Ni and Co) on the optical and electrical properties of f... more The effects of adding transition metals (Ni and Co) on the optical and electrical properties of four thin films Ni 1.25 Fe 1.5 Ge 0.25 O 4 , Ni 1.5 Fe 1 Ge 0.5 O 4 , Co 1 Fe 1 Ge 0.5 O 4 and Co 1.25 Fe 1.5 Ge 0.25 O 4 are reported. X-ray diffraction was used to ascertain the amorphization nature of the deposited films. The optical absorption behavior of these films was studied from the transmission and reflection in the range 200 -1100 nm. It was found that the optical band gap increases on increasing GeO 2 and arises from direct forbidden transitions. The opposite trend was found with the band tail width of the localized state. Optical constant parameters such as refractive index and absorption index were obtained for the films. The results for the alternatingcurrent (ac) conductivity and the dielectric constant of the four films are presented over the temperature range 277 -357 K and the frequency range 0.1 to 1000 kHz. The ac conductivity increases with temperature and frequency and decreases with the increase in Ni 2+ or Co 2+ content. The effect of composition and temperature on the dielectric constant was also studied. The frequency variation of the dielectric constant does not have a peak, unlike many semiconductor glasses.

Physica B: Condensed Matter, 2007

ABSTRACT The crystallization kinetics of As30Se70−xSnx chalcogenide glasses where x=0, 1, 2 and 3... more ABSTRACT The crystallization kinetics of As30Se70−xSnx chalcogenide glasses where x=0, 1, 2 and 3 have been discussed under non-isothermal conditions by differential thermal analysis (DTA). From the heating rate dependence of the glass transition temperature (Tg) and the crystallization temperature (Tc), the values of the activation energy of glass transition (Eg) and activation energy of crystallization (Ec) are evaluated. Most of the above mentioned glassy compounds have three-dimensional growth mechanism, according to the average value of Avrami index (n). The calculated average values of activation energies of crystallization have been used for the estimation of the thermal stability as well as the glass-forming tendency.