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Search Results: 1 - 10 of 198038 matches for " N. Hakem "
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Experimental Characterization of Ultra-Wideband Channel Parameter Measurements in an Underground Mine
B. Nkakanou,G. Y. Delisle,N. Hakem
Journal of Computer Networks and Communications , 2011, DOI: 10.1155/2011/157596
Abstract: Experimental results for an ultra-wideband (UWB) channel parameters in an underground mining environment over a frequency range of 3?GHz to 10?GHz are reported. The measurements were taken both in LOS and NLOS cases in two different size mine galleries. In the NLOS case, results were acquired for different corridor obstruction angles. The results were obtained during an extensive measurement campaign in the UWB frequency, and the measurement procedure allows both the large- and small-scale parameters such as the path loss exponent, coherence bandwidth, and so forth, to be quantified. The capacity of the UWB channel as a function of the physical depth of the mine gallery has also been recorded for comparison purposes. 1. Introduction Ultra-wideband (UWB) radio is a technology that has attracted a great deal of interest from academia, industry, and global standardization bodies over the recent years. The FCCs are defined as UWB signals having 10?dB bandwidth greater than 25% of their center frequencies of the radiation [1]. Ultra-wideband is a wireless technology that has offered many advantages, mainly the high-speed data transmissions, short-duration pulse, low-power spectral density, and large instantaneous bandwidth. Theses specifications allow coexistence with other existing technologies and enable fine time resolution. Many studies have shown that UWB is a good candidate for short-range multiple-access communications in dense multipath environments [2–4]. The potential of UWB system provides the following features: multiple accesses due to wide transmission bandwidths, accurate position location and ranging, lack of significant multipath fading due to fine delay resolution, and protected communications due to low transmission power. In order to establish a suitable model for the ultra-wideband channel behavior which is used when designing WB communications systems to support applications in underground mine environment, it is then important to have a thorough understanding of the propagation channel constraints. In recent years, several measurement campaigns to characterize the mining channel were conducted by the Télébec Underground Communications Research Laboratory (LRTCS) located in the mining area of Val-d’Or, QC, Canada [5, 6]. This laboratory, specialized in complex confined area communication, has at its disposal a unique experimental mine (CANMET-Canadian Centre for Minerals and Energy Technology). Characterization of channel propagation in underground environments has been an area of research since many years, but these studies have been
Enslavement of Wireless Sensor Network to an RF Energy Harvesting System  [PDF]
Alex Mouapi, Nadir Hakem
Open Journal of Antennas and Propagation (OJAPr) , 2017, DOI: 10.4236/ojapr.2017.52006
Abstract: The abundance of telecommunications systems makes it possible to have somewhat significant quantity of radiofrequency energy in the environment. This energy can be recycled to power ultra-low-power devices such as Wireless Sensor Network (WSN). In this paper, the performance of a miniature RF/DC converter is evaluated in order to enslave a WSN’s per-formance to the amount of the recovered energy. More precisely, a highly sensitive and efficient rectifier is designed to achieve optimum performance in the GSM band. The design method relies on a judicious choice of the rectifying diode which is the basis of most losses in a rectifying antenna (rectenna). Optimum performance is achieved by using the gradient method search proposed in the Advanced Design System (ADS) software. A rectifier based on Schottky diodes HSMS 2850 used in a voltage doubler topology is thus obtained. A maximum RF/DC conversion efficiency of 36% is reached for an RF input power level of 10 dBm. An energy budget of a sensor node in a WSN having an equitable distribution of network loads is then defined and used to evaluate the performance of the WSN regarding the distance at which the Base Station (BS) can be located. The Low Energy Adaptive Clustering Hierarchy (LEACH) protocol is used for this purpose. The distance separating the WSN from the BS is used as the enslavement parameter. Our analysis shows that increasing the duration of each round results in an increase in the range of the WSN. As an example, a network with 100 nodes distributed over an area of may be located at 1.3 km from the base station when each node of the WSN must perform measurements every 1 min.
Autonomous Wireless Sensors Network Based on Piezoelectric Energy Harvesting  [PDF]
Alex Mouapi, Nadir Hakem, Gilles Y. Delisle
Open Journal of Antennas and Propagation (OJAPr) , 2016, DOI: 10.4236/ojapr.2016.43011
Abstract: Wireless sensor networks (WSNs) offer an attractive solution to many environmental, security and process monitoring. However, their lifetime remains very limited by battery capacity. Through the use of piezoelectric energy harvesting techniques, ambient vibration can be captured and converted into usable electricity to create selfpowering WSN which is not limited by finite battery energy. This paper investigates analytically and experimentally the performance of a WSN powered by a Piezoelectric Energy Harvesting System (PEHS) and a material block-level modeling considering most key energy consumption of a wireless sensor node in a star topology network is proposed. By using real hardware parameters of existing components, the proposed model is used to evaluate the energetic budget of the node. The sensor node performance is evaluated regarding transmit packet size, duty cycle and the number of nodes that can be deployed. From the spectral properties of the available vibration inside two moving vehicles (automobile and train), the maximal recoverable power for each type of vehicle is estimated. Using a PEHS based on a cantilever beam optimized for low-frequency applications, 6 mW power is recovered in the case of the train while a 12.5 mW power is reached in the case of the automobile. It is observed that the sink may not operate with the recovered energy. However, the sensor node can sense and transmit data with a maximum size of 105.5 kbits when the duty cycle is 4 × 10-15. It is also achieved that the node is most effective when the measured physical phenomena vary slowly, such as the variations in temperature due to thermal inertia. Considering an optimized PEHS based on non-linear processing, it is shown that the sink can operate for 190% improvement of the recovered power.
60 GHz Polarization Reconfigurable DRA Antenna  [PDF]
Taieb Elkarkraoui, Gilles Y. Delisle, Nadir Hakem
Open Journal of Antennas and Propagation (OJAPr) , 2016, DOI: 10.4236/ojapr.2016.44014
Abstract: This paper outlines a new polarization reconfigurable EBG (Electromagnetic Band Gap) antenna in the 60 GHz millimeter waves band. The proposed hybrid antenna is composed of a multilayer pyramidal DRA (Dielectric Resonator Antenna) exciting source covered with a FSS (frequency Selective Surface) superstrate. The device can switch between circular and linear polarization by a simple 45° mechanical rotation of the pyramidal DRA. This structure has the advantage that it maintained stable bandwidth, gain, efficiency and radiation properties when switching between the two configurations of circular and linear polarization.
Non-existence of Global Solutions to a Wave Equation with Fractional Damping
Mohamed Berbiche,Ali Hakem
IAENG International Journal of Applied Mathematics , 2011,
On the Blow-up Behavior of Solutions to Semi-linear Wave Models with Fractional Damping
Ali Hakem,Mohamed Berbiche
IAENG International Journal of Applied Mathematics , 2011,
Studies on Degradation of Diquat Pesticide in Aqueous Solutions Using Electrochemical Method  [PDF]
Nasser Abu Ghalwa, Hazem M. Abu-Shawish, Mazen Hamada, Khaled Hartani, Abed Al Hakem Basheer
American Journal of Analytical Chemistry (AJAC) , 2012, DOI: 10.4236/ajac.2012.32014
Abstract: The C/PbO2 electrode assisted electrochemical removal of diquat dibromide herbicides solutions has been the subject of the present investigation under several operating conditions. The optimum conditions of the treatment process are: current density of 150 mA/cm2, pH 2.2, NaCl concentration 2 g/L, temperature of 10?C and initial diquat concentration of 50 mg/L. The time of electrolysis is 60 min for degradation rate of diquat and chemical oxygen demand (COD) removal is 210 min. The results were obtained by UV-Vis spectrophotometer and the present designed electrode was coincident.
DNA double-strand break signaling and human disorders
Toshiyuki Bohgaki, Miyuki Bohgaki, Razqallah Hakem
Genome Integrity , 2010, DOI: 10.1186/2041-9414-1-15
Abstract: Mammalian cells and organisms have evolved elegant ways to maintain their genomic integrity and respond to the various DNA lesions that they continuously face. DNA damage can result from exogenous stresses, such as ionizing radiation (IR), ultraviolet (UV) light and chemical compounds, or from endogenous insults such as reactive oxygen species (ROS) and DNA replication errors [1].DNA double-strand breaks (DSBs) are among the most serious and lethal types of DNA damage, as a single DSB is sufficient to kill a cell or disturb its genomic integrity [1]. DSBs are generated in response to exogenous and endogenous DNA insults. For instance, DSBs are induced in response to oncogenic activation [2]. In human precancerous lesions, oncogene activation has been shown to lead to continuous formation of DNA DSBs [3,4]. These DSBs activate the tumor suppressor p53 that mediate apoptosis and/or senescence to restrain the growth of the precancerous cells. In the presence of additional mutations that inactivate p53, precancerous cells become cancerous as they escape p53 mediated apoptosis and/or senescence [5,6]. In addition to the induced DSBs, there are also programmed DSBs that are critical for physiological processes such as meiosis and T and B-cell receptor rearrangements [7,8].DNA damage response (DDR) to various types of DNA insults is a well orchestrated process and is required to maintain genomic integrity (Figure 1) [9-12]. In response to DSBs, a signaling process activates cell cycle checkpoints and pauses cell cycle progression, thus granting time for damaged cells to repair their DNA (Figure 2 and section 2s) [13]. Two major repair pathways for DSBs exist in mammalian cells; the homologous recombination (HR) and the non-homologous end-joining (NHEJ) pathways [14]. The HR pathway is error free but requires an intact homologous template such as a sister chromatid. The NHEJ recombination pathway is the prominent pathway for DSB repair in mammalian cells; however this pathw
Role of Pirh2 in Mediating the Regulation of p53 and c-Myc
Anne Hakem ,Miyuki Bohgaki equal contributor,nédicte Lemmers equal contributor,Elisabeth Tai equal contributor,Leonardo Salmena,Elzbieta Matysiak-Zablocki,Yong-Sam Jung,Jana Karaskova,Lilia Kaustov,Shili Duan,Jason Madore,Paul Boutros,Yi Sheng,Marta Chesi,P. Leif Bergsagel,Bayardo Perez-Ordonez,Anne-Marie Mes-Masson,Linda Penn,Jeremy Squire,Xinbin Chen,Igor Jurisica,Cheryl Arrowsmith,Otto Sanchez,Samuel Benchimol,Razqallah Hakem
PLOS Genetics , 2011, DOI: 10.1371/journal.pgen.1002360
Abstract: Ubiquitylation is fundamental for the regulation of the stability and function of p53 and c-Myc. The E3 ligase Pirh2 has been reported to polyubiquitylate p53 and to mediate its proteasomal degradation. Here, using Pirh2 deficient mice, we report that Pirh2 is important for the in vivo regulation of p53 stability in response to DNA damage. We also demonstrate that c-Myc is a novel interacting protein for Pirh2 and that Pirh2 mediates its polyubiquitylation and proteolysis. Pirh2 mutant mice display elevated levels of c-Myc and are predisposed for plasma cell hyperplasia and tumorigenesis. Consistent with the role p53 plays in suppressing c-Myc-induced oncogenesis, its deficiency exacerbates tumorigenesis of Pirh2?/? mice. We also report that low expression of human PIRH2 in lung, ovarian, and breast cancers correlates with decreased patients' survival. Collectively, our data reveal the in vivo roles of Pirh2 in the regulation of p53 and c-Myc stability and support its role as a tumor suppressor.
Genome Integrity - a new open access journal
Razqallah Hakem, M Prakash Hande, John Petrini, Predrag Slijepcevic
Genome Integrity , 2010, DOI: 10.1186/2041-9414-1-1
Abstract: By launching Genome Integrity, the first open access journal dedicated to the field of DNA damage response and associated processes, we aim to provide interested scientists with the journal that enables (i) immediate online access to articles as soon as they are accepted for publication and (ii) free and universal online access resulting in dissemination to the widest possible audience. We believe that the current lack of opportunities for immediate and free dissemination of articles focusing on the above area of research will make Genome Integrity a viable and competitive journal. We would like to note that Genome Integrity articles will be archived in PubMed [1] and all freely accessible full-text repositories. This complies with the policies of a number of funding bodies including the Wellcome Trust, NIH and Howard Hughes Medical Institute [2-5].The scope of Genome Integrity is wide and ambitious. We aim to attract articles focusing on all aspects of DNA damage response mechanisms, including mechanisms of DNA damage induction, sensing, signalling and repair, cell cycle check-point control, telomere maintenance and control of apoptosis. The journal also welcomes submissions which focus on mechanisms of chromosome stability maintenance and the effects of genotoxic stress on this stability. A growing area of research within the field is understanding DNA damage processing in the context of interphase nucleus chromatin and the journal certainly aims to attract authors interested in the mechanisms underlying these processes. Genome Integrity also intends to encourage publications from authors interested in exploring the effects of normal and pathological DNA damage responses on tissue homeostasis, cellular and organismal ageing and tumorigenesis in humans and in animal models. In brief, Genome Integrity will publish articles exploring fundamental, as well as translational, aspects of all processes behind DNA damage response, genome and chromosome stability maintenance
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