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Search Results: 1 - 10 of 3438 matches for " Ismahène Hamdi "
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Selective Reflection Spectroscopy on the UV Third Resonance Line of Cs : Simultaneous Probing of a van der Waals Atom-Surface Interaction Sensitive to Far IR Couplings and of Interatomic Collisions
Pedro Chaves De Souza Segundo,Ismahène Hamdi,Michèle Fichet,Daniel Bloch,Martial Ducloy
Physics , 2007, DOI: 10.1134/S1054660X07070134
Abstract: We report on the analysis of FM selective reflection experiments on the 6S1/2->8P3/2 transition of Cs at 388 nm, and on the measurement of the surface van der Waals interaction exerted by a sapphire interface on Cs(8P3/2). Various improvements in the systematic fitting of the experiments have permitted to supersede the major difficulty of a severe overlap of the hyperfine components, originating on the one hand in a relatively small natural structure, and on the other hand on a large pressure broadening imposed by the high atomic density needed for the observation of selective reflection on a weak transition. The strength of the van der Waals surface interaction is evaluated to be 73$\pm$10 kHz.$\mu$m3. An evaluation of the pressure shift of the transition is also provided as a by-product of the measurement. We finally discuss the significance of an apparent disagreement between the experimental measurement of the surface interaction, and the theoretical value calculated for an electromagnetic vacuum at a null temperature. The possible influence of the thermal excitation of the surface is evoked, because, the dominant contributions to the vW interaction for Cs(8P3/2) lie in the far infrared range.
Dicke Coherent Narrowing in Two-Photon and Raman Spectroscopy of Thin Vapour Cells
Gabriel Dutier,Petko Todorov,Ismahène Hamdi,Isabelle Maurin,Solomon Saltiel,Daniel Bloch,Martial Ducloy
Physics , 2005, DOI: 10.1103/PhysRevA.72.040501
Abstract: The principle of coherent Dicke narrowing in a thin vapour cell, in which sub-Doppler spectral lineshapes are observed under a normal irradiation for a l/2 thickness, is generalized to two-photon spectroscopy. Only the sum of the two wave vectors must be normal to the cell, making the two-photon scheme highly versatile. A comparison is provided between the Dicke narrowing with copropagating fields, and the residual Doppler-broadening occurring with counterpropagating geometries. The experimental feasibility is discussed on the basis of a first observation of a two-photon resonance in a 300 nm-thick Cs cell. Extension to the Raman situation is finally considered.
Testing the distance-dependence of the van der Waals interaction between an atom and a surface through spectroscopy in a vapor nanocell
Athanasdios Laliotis,Isabelle Maurin,Petko Todorov,Ismahène Hamdi,Gabriel Dutier,Alexander Yarovitski,Solomon Saltiel,Marie-Pascale Gorza,Michèle Fichet,Martial Ducloy,Daniel Bloch
Physics , 2007, DOI: 10.1117/12.726798
Abstract: This paper presents our current measurements in a vapor nanocell aiming at a test of the distance-dependence of the atom-surface interaction, when simple asymptotic descriptions may turn to be not valid. A state-of-the-art of atom-surface interaction measurements is provided as an introduction, along with the comparison with the theory of the van der Waals (or Casimir-Polder) interaction; it is followed by a presentation of the most salient features of nanocell spectroscopy
Exploring the van der Waals Atom-Surface attraction in the nanometric range
Michèle Fichet,Gabriel Dutier,Alexander Yarovitski,Petko Todorov,Ismahène Hamdi,Isabelle Maurin,Solomon Saltiel,David Sarkisyan,Marie-Pascale Gorza,Daniel Bloch,Martial Ducloy
Physics , 2006, DOI: 10.1209/0295-5075/77/54001
Abstract: The van der Waals atom-surface attraction, scaling as C3 z-3 for z the atom-surface distance, is expected to be valid in the distance range 1-1000 nm, covering 8-10 orders of magnitudes in the interaction energy. A Cs vapour nanocell allows us to analyze the spectroscopic modifications induced by the atom-surface attraction on the 6P3/2->6D5/2 transition. The measured C3 value is found to be independent of the thickness in the explored range 40-130 nm, and is in agreement with an elementary theoretical prediction. We also discuss the specific interest of exploring short distances and large interaction energy.
Laser spectroscopy with nanometric gas cells : distance dependence of atom-surface interaction and collisions under confinement
Ismahène Hamdi,Petko Todorov,Alexander Yarovitski,Gabriel Dutier,Isabelle Maurin,Solomon Saltiel,Yuanyuan Li,Arturo Lezama,Tigran Varzhapetyan,David Sarkisyan,Marie-Pascale Gorza,Michèle Fichet,Daniel Bloch,Martial Ducloy
Physics , 2005,
Abstract: The high sensitivity of Laser Spectroscopy has made possible the exploration of atomic resonances in newly designed "nanometric" gas cells, whose local thickness varies from 20nm to more than 1000 nm. Following the initial observation of the optical analogous of the coherent Dicke microwave narrowing, the newest prospects include the exploration of long-range atom surface van der Waals interaction with spatial resolution in an unprecedented range of distances, modification of atom dielectric resonant coupling under the influence of the coupling between the two neighbouring dielectric media, and even the possible modification of interatomic collisions processes under the effect of confinement.
Heterogeneous Security Policy Validation: From Formal to Executable Specifications
Jihène Krichène,Mohamed Hamdi,Noureddine Boudriga
Journal of Networks , 2008, DOI: 10.4304/jnw.3.8.55-69
Abstract: This paper develops a prototyping technique for information systems security policies. Starting from the algebraic specification of a security policy, we derive an executable specification that represents a prototype of the actual policy. Executing the specification allows determining sequences of actions that lead to security policy violations. We propose a composition framework to build compound algebraic specifications. We show that the mechanism we provide to translate algebraic specifications to executable specifications preserves the composition rules, which is of utmost importance from the engineering perspective. Through accurate examples, we show how executables specifications can be used in conjunction with formal specification in the frame of the security policy engineering process.
A note on calculating autocovariances of periodic ARMA models
Abdelhakim Aknouche Hacène Belbachir Fay?al Hamdi
Statistics , 2007,
Abstract: An analytically simple and tractable formula for the start-up autocovariances of periodic ARMA (PARMA) models is provided.
Joint Power Allocation and Beamforming for Cooperative Networks  [PDF]
Sondes Maadi, Noureddine Hamdi
Int'l J. of Communications, Network and System Sciences (IJCNS) , 2011, DOI: 10.4236/ijcns.2011.47053
Abstract: In this paper, we investigate power allocation problem with the use of transmit beamforming in a dual hop MISO (multiple input single output) relay channel. We consider either amplify and forward (AF) or decode and forward (DF) cooperative protocols at the relay and optimize the power allocated to the relay and the source, under total transmit power constraint, to minimize the bit error rate (BER) of relaying system. Cooperative communication is viewed as a method for increasing diversity gain and reducing end to end path loss. The use of relay can create a virtual antenna array so that it allows users to exploit the advantages of multiple input multiple output (MIMO) techniques. In this work, we solve cooperative ratio, which is defined as the ratio power used for cooperative transmission over the total power. This approach is then compared to an equal power assignment method and its performance enhancement is verified by simulation results.
Estimating Urban Heat Island Effects on the Temperature Series of Uccle (Brussels, Belgium) Using Remote Sensing Data and a Land Surface Scheme
Rafiq Hamdi
Remote Sensing , 2010, DOI: 10.3390/rs2122773
Abstract: In this letter, the urban heat island effects on the temperature time series of Uccle (Brussels, Belgium) during the summers months 1960–1999 was estimated using both ground-based weather stations and remote sensing imagery, combined with a numerical land surface scheme including state-of-the-art urban parameterization, the Town Energy Balance Scheme. Analysis of urban warming based on remote sensing method reveals that the urban bias on minimum temperature is rising at a higher rate, 2.5 times (2.85 ground-based observed) more, than on maximum temperature, with a linear trend of 0.15 °C (0.19?°C ground-based observed) and 0.06 °C (0.06 °C ground-based observed) per decade respectively. The results based on remote sensing imagery are compatible with estimates of urban warming based on weather stations. Therefore, the technique presented in this work is a useful tool in estimating the urban heat island contamination in long time series, countering the drawbacks of a ground-observational approach.
The Growth of the Freshwater Crayfish (Astacus leptodactylus Eschscholtz, 1823) Juveniles Until the First Sexual Maturity Age in Concrete Fish Ponds
Hamdi Aydin
Journal of Animal and Veterinary Advances , 2012, DOI: 10.3923/javaa.2010.1720.1723
Abstract: In this study, freshwater crayfish (Astacus leptodactylus, Eschscholtz,1823) juveniles reared until the first sexual maturity age in the concrete fish ponds and growth and survival rates were investigated. The juvenile crayfish with initial weights of 67±3.48 mg and total lengths 10.1±0.4 mm (2130 pieces) was put into two concrete ponds, 400x140x75 cm in sizes and fed with trout food and fresh trout meat 3 times a week. The juvenile crayfish hatched until the 1st week of June, reached 1.038±0.23 g weight and 4.82±0.02 cm total length in the 1st year, 6.320±0.43 g weight and 6.34±0.80 cm total length in the 2nd year and 21.97±4.21 g weight and 9.81±1.93 cm total length in the 3rd year. At the end of the third year it was observed that 62 crayfish out of 97 laid eggs and the rate of survivals were 10.44% (97 female, 137 male).
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