Direct measurement of the g factor of composite fermions

The activation gap Delta of the fractional quantum Hall states at constant fillings nu=2/3 and 2/5 has been measured as a function of the perpendicular magnetic field B. A linear dependence of Delta on B is observed while approaching the spin-polarization transition. This feature allows a direct measurement of the g factor of composite fermions which appears to be heavily renormalized by interactions and strongly sensitive to the electronic filling factor.     

Steps on current-voltage characteristics of a silicon quantum dot covered by natural oxide

Considering a double-barrier structure formed by a silicon quantum dot covered by natural oxide with two metallic terminals, we derive simple conditions for a steplike voltage-current curve. Due to standard chemical properties, doping phosphorus atoms located in a certain domain of the dot form geometrically parallel current channels. The height of the current step typically equals (1.2 pA)N, where N=0, 1, 2, 3... is the number of doping atoms inside the domain, and only negligibly depends on the actual position of the dopants. The found conditions are feasible in experimentally available structures.     

Subthreshold carrier-LO phonon dynamics in semiconductors with intermediate polaron coupling: a purely quantum kinetic relaxation channel

Femtosecond transmission spectra of highly polar CdTe are compared to more covalent GaAs contrasting semiclassical kinetics with two-time quantum kinetics based on the Dyson equation. Nonequilibrium heavy holes in CdTe show ultrafast energy redistribution via the Fr?hlich mechanism even if photoexcited below the LO phonon energy. This subthreshold relaxation is a genuine quantum kinetic effect. It gains importance if the polaron self-energy is comparable to the phonon energy. Conservation of the free-particle energies is not required under these conditions.     

Combination of glow-discharge and arc plasmas for CF4 abatement

Decomposition of CF₄ by glow-discharge and arc plasmas was studied using a tubular quartz reactor, a disk type, and a T-type quartz reactor. The effects of different metal electrodes, input voltage, and reactor type on the efficiency of CF₄ total destruction (DRE) were studied. The T-shape reactor was more efficient in CF₄ destruction than either the disk or tubular type due to a combined effect of glow discharge and arc plasmas. Several hydrogen and oxygen sources, such as H₂O, H₂, O₂, and CH₄, were used to convert CF₄. Using H₂ and O₂ as the hydrogen and oxygen sources presented better DRE than using H₂O. The effect of different hydrogen and oxygen sources on the conversion of CF₄ followed the trend: (H₂ + O₂) > (CH₄ + O₂) > H₂O. The maximum DRE of 95% was observed with 0.5% CF₄ using H₂ and O₂. A mass spectrometer and an emission spectroscope equipped with a charge-coupled detector (CCD) were used to characterize the products and intermediates. Mass spectrometric studies indicated that the reaction products were HF, CO₂, and trace amounts of NO. N₂ first negative and second positive emission lines were observed in the glow discharge plasmas as well as in the arc plasmas of N₂. However, C and F intermediates were observed only in arc plasmas of CF₄. Reactions occurring in the glow discharge plasmas and arcs seem to follow different mechanisms.     

Coupled Diffusion-Dissolution Around a Fracture Channel: The Solute Congestion Phenomenon

The paper studies the coupled diffusion-dissolution process in reactive porous media, separated by a fracture channel. An aggressive solute, corresponding for e.g., to a complete demineralization that dissolves the solid skeleton of the surrounding porous material, is prescribed at the inlet of the fracture. By means of asymptotic dimensional analysis it is shown that for large times the diffusion length in the fracture develops with the quadratic root of time. In comparison with the 1D-Stefan Problem, in which the dissolution front evolves with the square root of time, this indicates that the overall solute evacuation through the structure slows down in time. This phenomenon is referred to as a diffusive solute congestion in the fracture. This asymptotic behavior is confirmed by means of model-based simulation, and the relevant material parameters, related to only the chemical equilibrium condition, are identified. The obtained results suggest that the presence of a small crack does not significantly increase the propagation of the dissolution front in the porous bulk, and hence the overall chemical degradation of the porous material. The same applies to other diffusion induced demineralization, mineralization, sorption and melting processes, provided that the convective transport of the solute in the crack is small in comparison with the solute diffusion. The result is relevant for several problems in durability mechanics: calcium leaching of concrete in nuclear waste containment, mineralization and demineralization in bone remodeling, chloride penetration, etc.     

Determination of the food carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in human hair by solid-phase extraction and gas chromatography-mass spectrometry

Summary A method for the determination of the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in human hair has been developed and validated. Hair samples (200 mg) were dissolved in NaOH (1 M) and PhIP was isolated by successive solid-phase extraction on a polystyrene-divinylbenzene column and on a silica-based mixed-mode column with C₈ and-SO₃ ⁻ functional groups. Quantification was performed by gas chromatography-electron-impact ionization high-resolution mass spectrometry in selected-ion-monitoring mode. The method was validated for determination of PhIP in the concentration range 0.5–25 ng g⁻¹ hair with [²H₃]PhIP as internal standard. The limit of quantification was 0.26 ng g⁻¹ hair. Within-day and between-day precision were in the ranges 1–27% and 2–15% relative standard deviation, respectively. The hair sample used for method validation was found to contain 0.26 ng PhIP g⁻¹ hair.     

Explicit approximations of the indentation modulus of elastically orthotropic solids for conical indenters

The elastic problem of the contact between an axisymmetric indenter and a general anisotropic (21 independent elastic constants) half space has not been solved explicitly in closed form. Implicit methods to determine the indentation modulus originate from the work of Willis [J. Mech. Phys. Solids 14 (1966) 163]; and are now available for conical, parabolic and spherical indenters [Philos. Mag. A 81 (2001) 447; J. Mech. Phys. Solids 51 (2003) 1701]. The particular case of orthotropy has also been investigated [ASME J. Tribol. 115 (1193) 650, 125 (2003) 223]. This paper proposes an explicit solution for the indentation moduli of a transversely isotropic medium and a general orthotropic medium under rigid conical indentation in the three principal material symmetry directions. The half-space Green’s functions are interpolated from their exact extreme values, then integrated and finally simplified. The proposed closed form expressions are in very good agreement with the implicit solution schemes of [Philos. Mag. A 81 (2001) 447; J. Mech. Phys. Solids 51 (2003) 1701].     

Rheological properties of branched polystyrenes: linear viscoelastic behavior

Oscillatory shear measurements on a series of branched graft polystyrenes (PS) synthesized by the macromonomer technique are presented. The graft PS have similar molar masses (M _w between 1.3×10⁵ g/mol and 2.4×10⁵ g/mol) and a polydispersity M _w /M _n around 2. The molar masses of the grafted side chains M _w,br range from 6.8×10³ g/mol to 5.8×10⁴ g/mol, which are well below and above the critical entanglement molar mass M _c of linear polystyrene. The average number of side chains per molecule ranges from 0.6 to 6.7. The oscillatory measurements follow the time–temperature superposition principle. The shift factors do not depend on the number of branches. The zero-shear viscosities of all graft PS are lower than those of linear PS with the same molar mass, which can be attributed to the smaller coil size of the branched molecules. It is shown that the influence of branching on the frequency dependence of the dynamic moduli is weak for all graft PS that were investigated, which can be explained by the low entanglement density.Electronic Supplementary Material Supplementary material is available for this article at This article has already been published online first (DOI: ). Due to an oversight at the publisher's, this version contained several mistakes. The article is herewith republished in its entirety as a "publisher's erratum".     

A micromechanical analysis of damage propagation in fluid-saturated cracked mediaUne analyse micromécanique de la propagation de l'endommagement d'une fissure sous pression de fluide

We first revisit the well known framework of Linear Elastic Fracture Mechanics (LEFM) in the case of a fluid-saturated crack. We next consider a r.e.v. of cracked medium comprising a family of cracks characterized by the corresponding crack density parameter ε. Generalizing the classical energy approach of LEFM, the proposed damage criterion is written on the thermodynamic force associated with ε, which is estimated by means of standard homogenization schemes. This criterion proves to involve a macroscopic effective strain tensor, or alternatively the Terzaghi effective stress tensor. The stability of damage propagation is discussed for various homogenization schemes. A comparison with experimental results is presented in the case of a uniaxial tensile test on concrete. To cite this article: L. Dormieux et al., C. R. Mecanique 334 (2006).     

An interferometric study of thermal stratification by natural convection in a contained liquid

Transient laminar free convection to water in a rectangular container was investigated using a Mach-Zehnder interferometer. The experimental y observed temperature profiles are compared with analytically predicted profiles based on a computer program developed byBarakat. Good agreement between analysis and experiment was obtained. In addition qualitative observations of the conditions in the container during sudden discharge of the liquid are reported.

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Zusammenfassung Untersucht wurde der nichtstationäre, laminare Wärmeübergang durch freie Konvektion in Wasser in einem rechteckigen Behälter mittels eines Zehnder-Mach-Interferometers. Die im Experiment beobachteten Temperaturprofile wurden mit den analytisch vorausgesagten Profilen verglichen, die mit einem Komputerprogramm, das vonBarakat entwickelt wurde, erzielt wurden. Gute Übereinstimmung zwischen Analyse und Experiment wurde erreicht. Außerdem werden qualitative Beobachtungen der Vorgänge im Behälter während des plötzlichen Leerens der geschichteten Behälterflüssigkeit berichtet.