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Search Results: 1 - 10 of 581 matches for " Walid Allag "
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Optimization of Parameters CO2 Laser for Drilling Different Types of Glass  [PDF]
Nafissa Khennafi-Benghalem, Walid Allag
New Journal of Glass and Ceramics (NJGC) , 2015, DOI: 10.4236/njgc.2015.54009
Abstract: The aim of this work is to study in detail the drilling process on glass by CO2 laser. The study parameters considered in the present experiments are based on the laser beam power of range (30% - 80% of 25 W) and an exposure time for drilling (2 - 8 s). The measured diameters of holes by optical methods are between [300 - 800 μm]. The results obtained by optical observations suggest that ordinary and mineral glasses cannot withstand to a contact of the laser beam and crack during the formation of the drilling hole. The minimum power and duration of exposure are the optimal parameters for drilling the organic glass, we observe no micro-cracks, and again we see that the edges of the holes have a good surface quality with a high aspect ratio.
Analytical Calculation of the Energy in a Permanent Magnet  [PDF]
Jean-Paul Yonnet, Christian Chillet, Hicham Allag, Lotfi Chouikhi
Journal of Modern Physics (JMP) , 2016, DOI: 10.4236/jmp.2016.716196
Abstract: The energy in permanent magnet is not a trivial problem because it exist two types of energy: the field energy and the demagnetizing energy. For parallelepiped shape, the magnet energy has been calculated by fully analytical expressions in 3D. The result has been obtained after four successive integrations of Arctangent and Logarithm functions. The analytically calculated energy corresponds to the demagnetization energy in the magnet. The analytical results have been compared with different terms of energy obtained by computation.
Differentially-Keyed IR-UWB Signals for MA with Differential-Detection Receiver  [PDF]
Walid Mahmoud
Journal of Computer and Communications (JCC) , 2014, DOI: 10.4236/jcc.2014.28004

Noncoherent communication receivers (differential-detectors) have simple design, however, they always incur bit error rate (BER) performance loss up to 3dB compared to coherent receivers. In this paper, a differential-detector is proposed for impulse radio ultra wideband (IR-UWB) communication systems. The system employs bit-level differential phase shift keying (DPSK) combined with code division (CD) for IR-UWB signals to support multiple-access (MA). It is analyzed under additive white Gaussian noise (AWGN) corrupted by multiple-access interference (MAI) channel. Its BER performance is compared against a reference coherent receiver using Monte-Carlo simulation method. A closed form expression for its average probability of error is derived analytically. Simulation results and theoretical analysis confirm the applicability of the proposed differential-detector for IR-UWB communication systems.

The Relationship of SmokingOpioidAntidepressant Use and History of Spine Surgery  [PDF]
Walid Mohammad, Zaytseva Nadezhda
International Journal of Clinical Medicine (IJCM) , 2010, DOI: 10.4236/ijcm.2010.11003
Abstract: Introduction: In a recent paper, smoking was shown to be an independent predictor of longterm continued opioid use in spine patients (Krebs et al. 2010). In this paper, we study the interaction of smoking with opioid and antidepressant use and the relationship with prior spine surgery and future spine surgery. Methods: Data on smoking, opioid and antidepressant use were retrospectively collected from 758 spine surgery inpatients [lumbar microdiskectomy (LMD), anterior cervical decompression and fusion (ACDF) and lumbar decompression and fusion (LDF)]. Interaction with history of previous spine surgery and return for additional spine surgery was studied. Followup ranged from one to four years. Results: Significant correlation was detected between smoking and opioid use and between opioid and antidepressant use. History of previous spine surgery correlated with antidepressant use and return for additional spine surgery. Additional spine surgery correlated with opioid use and history of previous spine surgery. Smoking LMD patients on both opioids and antidepressants and smoking ACDF patients on antidepressants who have a history of prior spine surgery were more likely to return for additional spine surgery. However, in the LDF group, smoking patients on antidepressants without previous spine surgery were more likely to come for another spine surgery. Conclusion: Smokingantidepressantopioid use could be predictive of return for additional spine surgery during the followup years especially if a history of prior spine surgery was reported. Further research is needed on the implications of such an association.
Dependence of the GRB Lag-Luminosity Relation on Redshift in the Source Frame  [PDF]
Walid J. Azzam
International Journal of Astronomy and Astrophysics (IJAA) , 2012, DOI: 10.4236/ijaa.2012.21001
Abstract: The lag-luminosity relation for gamma-ray bursts (GRBs) is an anti-correlation between the time lag, ?lag, which represents the delay between the arrival of hard and soft photons, and the isotropic peak luminosity, L. In this paper, we use a sample of 43 Swift bursts, which was taken from Ukwatta et al., to investigate whether this relation depends on redshift. Both the z-correction and the k-correction are taken into account. Our analysis consists of binning the data in redshift, z, then applying a fit of the form: for each bin, where ?lag0 is the time-lag in the burst’s source frame, and is the corresponding mean value for the entire sample. The goal is to see whether the two fitting parameters, A and B, evolve in a systematic way with z. Our results indicate that both the normalization, A, and the slope, B, seem to vary in a systematic way with redshift. We note that although good best-fits were obtained, with reasonable values for both the linear regression coefficient, r, and the reduced chi-squared, the data showed large scatter. Also, the number of GRBs in the sample studied is not large, and thus our conclusions are only tentative at this point. A flat universe with M = 0.27, ?? = 0.73, and a Hubble constant, H0 = 70 km.s-1.Mpc-1 is assumed.
On the Security of Anonymous Authentication Protocol for Mobile Pay-TV  [PDF]
Walid I. Khedr
Journal of Information Security (JIS) , 2013, DOI: 10.4236/jis.2013.44025

One of the promising multimedia services is the mobile pay-TV service. Due to its wireless nature, mobile pay-TV is vulnerable to attacks especially during hand-off. In 2011, an efficient anonymous authentication protocol for mobile pay-TV is proposed. The authors claim that their scheme provides an anonymous authentication to users by preventing intruders from obtaining usersIDs during the mutual authentication between mobile subscribers and head end systems. However, after analysis, it was found that the scheme does not provide anonymous authentication and users can be easily tracked while using their anonymous identity. The scheme is also subject to denial of service attack. In this paper the deficiencies of the original scheme are demonstrated, and then a proposed improved scheme that eliminates these deficiencies is presented.

A Brief Review of the Amati Relation for GRBs  [PDF]
Walid J. Azzam
International Journal of Astronomy and Astrophysics (IJAA) , 2016, DOI: 10.4236/ijaa.2016.64030
Abstract: Gamma-ray bursts (GRBs) are the most powerful explosions in the universe. Alt-hough the exact mechanism behind these explosions remains elusive, GRBs hold great promise as cosmological probes for two main reasons: they have been observed up to very high redshift (z > 9), and their gamma-ray emission is unencumbered by any intervening dust. Several GRB energy and luminosity indicators have been discovered. These indicators correlate an observable quantity, like the intrinsic peak energy, Ep,i, in the?\"\"spectrum of a burst to an unobservable parameter like the equivalent isotropic energy, Eiso, or the isotropic peak luminosity, Lp,iso. This paper provides a brief review of one of these energy and luminosity indicators, the Amati relation, and discusses its potential use as a cosmological probe.
Peak Energy Correlations for Gamma-Ray Bursts  [PDF]
Walid J. Azzam
Journal of Applied Mathematics and Physics (JAMP) , 2017, DOI: 10.4236/jamp.2017.58124
Abstract: Gamma-ray bursts (GRBs) are the most powerful explosions in the universe. Over the past two decades, several GRB energy and luminosity correlations were discovered. These correlations typically involve an observable parameter, like the observed peak energy, Ep,obs, and a non-observable quantity, like the equivalent isotropic energy, Eiso. This paper provides a brief review of GRB peak energy correlations. Specifically, it focuses on the Amati relation, which correlates Ep,obs and Eiso, and the Ghirlanda relation, which correlates Ep,obs and Ey, the total energy corrected for beaming. The paper also discusses the physical interpretation of these relations in the context of the internal shock model.
Invariant Relative Orbits Taking into Account Third-Body Perturbation  [PDF]
Walid Ali Rahoma, Gilles Metris
Applied Mathematics (AM) , 2012, DOI: 10.4236/am.2012.32018
Abstract: For a satellite in an orbit of more than 1600 km in altitude, the effects of Sun and Moon on the orbit can’t be negligible. Working with mean orbital elements, the secular drift of the longitude of the ascending node and the sum of the argu-ment of perigee and mean anomaly are set equal between two neighboring orbits to negate the separation over time due to the potential of the Earth and the third body effect. The expressions for the second order conditions that guaran-tee that the drift rates of two neighboring orbits are equal on the average are derived. To this end, the Hamiltonian was developed. The expressions for the non-vanishing time rate of change of canonical elements are obtained.
Extra Investigation Might Be Necessary in High-Risk CT-Negative Cerebrovascular Cases  [PDF]
Mohammad Sami Walid, Nadezhda Zaytseva
Neuroscience & Medicine (NM) , 2013, DOI: 10.4236/nm.2013.42017

Cerebrovascular accidents occur in elderly patients in whom neurodegenerative changes increase the risk of vascular permeation and concomitant intracranial bleeding. In rare cases, intracerebral massive hemorrhage happens in hospitalized patients with apparently stable clinical picture. We report two cases illustrating this phenomenon, discuss the possible pathomechanism involved in those tragic incidents and suggest possible prevention measures for these patients. A negative CT image in a patient with neurological symptoms, especially who are on warfarin with or without considerably elongated coagulation time, may be subject to a sudden intracranial hemorrhage. Microvascular abnormalities might be detected on perfusion CT imaging and should therefore be performed in all CT negative patients with close observation for 24 hours before contemplating discharge.

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