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Search Results: 1 - 10 of 1102 matches for " Raja Dahmane "
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Free Radicals and Extrinsic Skin Aging
Borut Polj?ak,Raja Dahmane
Dermatology Research and Practice , 2012, DOI: 10.1155/2012/135206
Abstract: Human skin is constantly directly exposed to the air, solar radiation, environmental pollutants, or other mechanical and chemical insults, which are capable of inducing the generation of free radicals as well as reactive oxygen species (ROS) of our own metabolism. Extrinsic skin damage develops due to several factors: ionizing radiation, severe physical and psychological stress, alcohol intake, poor nutrition, overeating, environmental pollution, and exposure to UV radiation (UVR). It is estimated that among all these environmental factors, UVR contributes up to 80%. UV-induced generation of ROS in the skin develops oxidative stress, when their formation exceeds the antioxidant defence ability of the target cell. The primary mechanism by which UVR initiates molecular responses in human skin is via photochemical generation of ROS mainly formation of superoxide anion , hydrogen peroxide (H2O2), hydroxyl radical ( ), and singlet oxygen . The only protection of our skin is in its endogenous protection (melanin and enzymatic antioxidants) and antioxidants we consume from the food (vitamin A, C, E, etc.). The most important strategy to reduce the risk of sun UVR damage is to avoid the sun exposure and the use of sunscreens. The next step is the use of exogenous antioxidants orally or by topical application and interventions in preventing oxidative stress and in enhanced DNA repair. 1. Introduction Human skin is naked and is constantly directly exposed to the air, solar radiation, other environmental pollutants, or other mechanical and chemical insults, which are capable of inducing the generation of free radicals as well as reactive oxygen species (ROS) of our own metabolism. A free radical can be defined as a chemical species possessing an unpaired electron [1]. It can also be considered as a fragment of a molecule. Free radicals, important for living organisms, include hydroxyl , superoxide , nitric oxide , thyl , and peroxyl . Peroxynitrite (ONOO?), hypochlorous acid (HOCl), hydrogen peroxide (H2O2), singlet oxygen , and ozone (O3) are not free radicals but can easily lead to free radical reactions in living organisms. The term reactive oxygen species (ROS) is often used to include not only free radicals but also the nonradicals ( , ONOO?, H2O2, and O3). Reactive oxygen species are formed and degraded by all aerobic organisms, leading to either physiological concentrations required for normal cell function or excessive quantities, state called oxidative stress. Oxidative stress is the term referring to the imbalance between generating of ROS and the
Sleeping on an Anti-Wrinkle Pillow Reduces Facial Wrinkles: Results from an Anatomical Study  [PDF]
Borut Poljsak, Aleksandar Godic, Rok Fink, Martina Oder, Tomaz Lampe, Raja Dahmane
Forensic Medicine and Anatomy Research (FMAR) , 2015, DOI: 10.4236/fmar.2015.32010
Abstract: Background: A special pillow was designed to redistribute mechanical stress during sleeping in order to slow down the formation of facial skin wrinkles. Objective: To investigate whether sleeping on a specially designed pillow reduces facial skin wrinkles. Participants and Methods: A 28-day pilot study was carried out in which fifteen healthy female volunteers aged 23 - 55 years (mean age 35. 6 ± 8.5) slept on an antiwrinkle pillow. Evaluation of facial wrinkles was conducted before commencing the study (T0), following at 14 days (T14), and at 28 days (T28) when the study ended. Wrinkle density was assessed by computerized analysis of 2D images of participants’ faces. Results: A statistically significant decrease in wrinkle density was detected while smiling around both eyes, around the right eye in a relaxed facial expression, on average in all observed facial areas, around the left periorbital area in participants who predominantly slept on their left side of the body, but not on the frontal area. Limitations: A 3D camera could be used to better visualize and analyze wrinkle density. Conclusions: Sleeping on the specially designed pillow reduces facial wrinkles.
?pela Sajko,Lucie Kubínová,Marko Kreft,Raja Dahmane
Image Analysis and Stereology , 2002, DOI: 10.5566/ias.v21.p7-12
Abstract: Stereological methods, based on the optical disector principle and fluorescent staining, were developed for estimating frequency of satellite cells in skeletal muscles. The parameter NL(sc, fib) (number of satellite cells per fibre length) was compared with the parameter NN(sc, nucl) (the percentage of satellite cell nuclei in all muscle nuclei), most often published in the literature, by applying unbiased sampling and counting procedures and using a confocal microscope. The methods were tested in autopsy samples of four young vs. four old human vastus lateralis muscles. Both parameters NL(sc, fib) and NN(sc, nucl) declined during ageing. However, it appears that the two parameters cannot be substituted one by the other because the number of nuclei per fibre length tends to be increased during aging. Using the introduced methods, it is more straightforward to estimate NL(sc, fib) than NN(sc, nucl).
Skin Photoaging and the Role of Antioxidants in Its Prevention
Ru?a Pandel,Borut Polj?ak,Aleksandar Godic,Raja Dahmane
ISRN Dermatology , 2013, DOI: 10.1155/2013/930164
Abstract: Photoaging of the skin depends primarily on the degree of ultraviolet radiation (UVR) and on an amount of melanin in the skin (skin phototype). In addition to direct or indirect DNA damage, UVR activates cell surface receptors of keratinocytes and fibroblasts in the skin, which leads to a breakdown of collagen in the extracellular matrix and a shutdown of new collagen synthesis. It is hypothesized that dermal collagen breakdown is followed by imperfect repair that yields a deficit in the structural integrity of the skin, formation of a solar scar, and ultimately clinically visible skin atrophy and wrinkles. Many studies confirmed that acute exposure of human skin to UVR leads to oxidation of cellular biomolecules that could be prevented by prior antioxidant treatment and to depletion of endogenous antioxidants. Skin has a network of all major endogenous enzymatic and nonenzymatic protective antioxidants, but their role in protecting cells against oxidative damage generated by UV radiation has not been elucidated. It seems that skin’s antioxidative defence is also influenced by vitamins and nutritive factors and that combination of different antioxidants simultaneously provides synergistic effect. 1. Introduction Unlike chronological aging, which is predetermined by individual’s physiological predisposition, photoaging depends primarily on the degree of sun exposure and on an amount of melanin in the skin. Individuals who have a history of intensive sun exposure, live in sunny geographical areas, and have fair skin will experience the greatest amount of ultraviolet radiation (UVR) skin load and consequently severe photoaging [1, 2]. Clinical signs of photoaging include wrinkles, mottled pigmentation (hypo- or hyperpigmentation), rough skin, loss of the skin tone, dryness, sallowness, deep furrows, severe atrophy, telangiectasias, laxity, leathery appearance, solar elastosis, actinic purpura, precancerous lesions, skin cancer, and melanoma [3, 4]. Sun-exposed areas of the skin, such as the face, neck, upper chest, hands, and forearms, are the sites where these changes occur most often [5]. Chronological skin aging, on the other hand, is characterized by laxity and fine wrinkles, as well as development of benign growths such as seborrheic keratoses and angiomas, but it is not associated with increased/decreased pigmentation or with deep wrinkles that are characteristic for photoaging [6]. Seborrheic keratoses are regarded as best biomarker of intrinsic skin aging since thier appearance is independent on sun exposure. While intrinsically aged skin does not
The Neglected Importance of Sleep on the Formation and Aggravation of Facial Wrinkles and Their Prevention  [PDF]
Borut Poljsak, Aleksandar Godic, Andrej Starc, Raja Dahmane
Journal of Cosmetics, Dermatological Sciences and Applications (JCDSA) , 2016, DOI: 10.4236/jcdsa.2016.63012
Abstract: The duration of sleep and the position of the face while resting on a pillow have a negative impact on the facial skin appearance and may lead to the formation of sleep wrinkles. Sleep lines occur when there is repetitive, long-term tension on the facial skin, which pushes or pulls the skin in a direction that is perpendicular to the direction of the muscles of the face. These lines tend to be more vertically oriented than expression lines and can be found on the forehead, around the eyebrows, the eyes, the cheeks, the chin, and the nasolabial folds. Our studies revealed that the average reduction of wrinkles in total investigated area of the face (expressed as the density of wrinkle per surface skin) was approximately 12% after 28 days of sleep on a specially-designed pillow. The specially designed anti-wrinkle pillows eliminate the pressure on the cheeks, the eyes and the mouth during sleep. Many such pillows have been designed to reduce the aging process and to encourage users to sleep in specific positions. Evidence supporting the claim that a special pillow prevents wrinkles was presented. Nevertheless, prolonged human studies are required to further elucidate the role of sleeping on appearance of facial wrinkles.
La mujer en la sociedad Nomada del Sur de Marruecos: enfoque etnográfico
Dahmane, Mohamed;
Cadernos Pagu , 2008, DOI: 10.1590/S0104-83332008000100004
Abstract: this article deals with the social position of women in the sahara area, in a nomad society that has passed through many socio-economic changes since the 1970s, therefore affecting women's status as well as gender relations in this traditional muslim society.
Enseignement/apprentissage des langues en Algérie entre représentations identitaires et enjeux de la mondialisation
Ait Dahmane Karima
Synergies Algerie , 2007,
Abstract: Aujourd’hui, le bilinguisme est une pratique recherchée dans les contextes internationaux pour pouvoir s’adapter et faire face aux enjeux de la mondialisation. Comment la politique linguistique algérienne s’adapte-t-elle aux nouvelles exigences pédagogiques et scienti ques ? C’est cette question préliminaire qui nous permettra de ré échir sur les représentations interculturelles dans la démarche d’enseignement/apprentissage des langues. Les premiers résultats de notre enquête ouvrent des perspectives dans la conception d’une didactique du plurilinguisme , liée au développement de la capacité plurilingue de chacun à des degrés de ma trise hétérogène, selon les besoins individuels de la vie professionnelle.
FPGA Implementation of Block Parallel DF-MPIC Detectors for DS-CDMA Systems in Frequency-Nonselective Channels
Adel Omar Dahmane,Lotfi Mejri
Journal of Electrical and Computer Engineering , 2008, DOI: 10.1155/2008/435756
Abstract: Multistage parallel interference cancellation- (MPIC-) based detectors allow to mitigate multiple-access interference in direct-sequence code-division multiple-access (DS-CDMA) systems. They are considered serious candidates for practical implementation showing a good tradeoff between performance and complexity. Better performance is obtained when decision feedback (DF) is employed. Although MPIC and DF-MPIC have the same arithmetic complexity, DF-MPIC needs much more FPGA resources when compared to MPIC without decision feedback. In this letter, FPGA implementation of block parallel DF-MPIC (BP-DF-MPIC) is proposed allowing better tradeoff between performance and FPGA area occupancy. To reach an uncoded bit-error rate of 10?3, BP-DF-MPIC shows a 1.5 dB improvement over the MPIC without decision feedback with only 8% increase in FPGA resources compared to 69% for DF-MPIC.
Spreading Code Assignment Strategies for MIMO-CDMA Systems Operating in Frequency-Selective Channels
D'Amours Claude,Dahmane AdelOmar
EURASIP Journal on Wireless Communications and Networking , 2009,
Abstract: Code Division Multiple Access (CDMA) and multiple input multiple output- (MIMO-) CDMA systems suffer from multiple access interference (MAI) which limits the spectral efficiency of these systems. By making these systems more power efficient, we can increase the overall spectral efficiency. This can be achieved through the use of improved modulation and coding techniques. Conventional MIMO-CDMA systems use fixed spreading code assignments. By strategically selecting the spreading codes as a function of the data to be transmitted, we can achieve coding gain and introduce additional degrees of freedom in the decision variables at the output of the matched filters. In this paper, we examine the bit error rate performance of parity bit-selected spreading and permutation spreading under different wireless channel conditions. A suboptimal detection technique based on maximum likelihood detection is proposed for these systems operating in frequency selective channels. Simulation results demonstrate that these code assignment techniques provide an improvement in performance in terms of bit error rate (BER) while providing increased spectral efficiency compared to the conventional system. Moreover, the proposed strategies are more robust to channel estimation errors as well as spatial correlation.
Bit Error Rate Performance of a MIMO-CDMA System Employing Parity-Bit-Selected Spreading in Frequency Nonselective Rayleigh Fading
Claude D'Amours,Adel Omar Dahmane
International Journal of Antennas and Propagation , 2011, DOI: 10.1155/2011/516929
Abstract: We analytically derive the upper bound for the bit error rate (BER) performance of a single user multiple input multiple output code division multiple access (MIMO-CDMA) system employing parity-bit-selected spreading in slowly varying, flat Rayleigh fading. The analysis is done for spatially uncorrelated links. The analysis presented demonstrates that parity-bit-selected spreading provides an asymptotic gain of dB over conventional MIMO-CDMA when the receiver has perfect channel estimates. This analytical result concurs with previous works where the (BER) is determined by simulation methods and provides insight into why the different techniques provide improvement over conventional MIMO-CDMA systems. 1. Introduction The object of much research in wireless communications is to enable users to transmit and receive at high and variable data rates to support the growing number of applications that involve such transfer of data [1]. Code Division Multiple Access (CDMA) systems employ spread spectrum (SS) technology and were developed for second and third generation (2G, 3G) wireless communications. For example, IS-95 and Wideband CDMA (WCDMA) systems are based on direct sequence SS techniques. Multiple access interference (MAI) is present in CDMA systems due to the nonzero cross-correlation between the different users' spreading codes [2]. The MAI that each user's signal creates in all other users' signals results in increased bit error rate (BER). The overall system capacity is determined by the number of simultaneous transmitters that can be supported before the BER increases to an unacceptable level [3]. Much research presented in the literature has concentrated on making systems more power efficient as a means to increase the overall spectral efficiency of the CDMA system [4–6]. Other techniques, such as multiuser detection, have also been considered to increase the capacity of CDMA systems [2, 7, 8]. Recent research has shown that combining DS-CDMA systems with Multiple Input Multiple Output (MIMO) techniques can achieve high gains in capacity, reliability and data transmission speed [9–14]. This is achieved by exploiting the spatial diversity made possible by multiple antennas at the transmitter and the receiver, allowing more degrees of freedom when the complex channel gains between different transmit and receive antenna pairs are sufficiently uncorrelated. MIMO-CDMA systems are also more robust to multiple access interference (MAI) than their single input single output (SISO) DS-CDMA counterparts. Currently, MIMO-CDMA is considered for many beyond 3G
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