Effective Average Action of Chern-Simons Field Theory

The renormalization of the Chern-Simons parameter is investigated by using an exact and manifestly gauge invariant evolution equation for the scale-dependent effective average action.Comment: 14 pages, late

Equilibration between edge states in the fractional quantum Hall effect regime at high imbalances

We experimentally study equilibration between edge states, co-propagating at the edge of the fractional quantum Hall liquid, at high initial imbalances. We find an anomalous increase of the conductance between the fractional edge states at the filling factor $\nu=2/5$ in comparison with the expected one for the model of independent edge states. We conclude that the model of independent fractional edge states is not suitable to describe the experimental situation at $\nu=2/5$.Comment: 4 page

Evidence for the Luttigger liquid density of states in transport across the incompressible stripe at fractional filling factors

We experimentally investigate transport across the incompressible stripe at the sample edge in the fractional quantum Hall effect regime at bulk filling factors $\nu=2/3$ and $\nu=2/5$. We obtain the dependence of the equilibration length, that is a phenomenological characteristics of the transport, on the voltage imbalance and the temperature, at high voltage imbalances. These dependencies are found to be of the power-law form, which is a strong evidence for the Luttigger liquid density of states.Comment: 4 pages, to appear in EP

Potentialités des bioélectrodes et des bioréacteurs à biomasse fixée pour l'estimation rapide de la DBO

La méthode standard de détermination de la Demande Biochimique en Oxygène (DBO-5 jours par dilutions) présente certains inconvénients bien connus dont celui de ne pas être exploitable pour la gestion en temps réel d'un procédé d'épuration. De ce fait, divers types d'appareils d'estimation rapide de la DBO, basés sur des méthodes respirométriques, ont été imaginés dans le passé et même commercialisés pour certains.Dans cette étude, des appareils d'estimation rapide de la DBO de types bioélectrode et réacteurs à biomasse fixée (écoulement piston et parfaitement mélangé) ont été mis en oeuvre, après avoir été développés ou modifiés sur base de concepts déjà existants. Une attention particulière a été portée sur la validité de ces appareils, la crédibilité de leurs mesures et la définition de leur champ d'action.De par leur principe de fonctionnement (injection en flux), la bioélectrode et le bioréacteur piston sont des appareils qui doivent être calibrés et dont la biomasse immobilisée doit être préalablement adaptée à l'échantillon à analyser. La solution de calibration est essentielle et doit être qualitativement la plus proche possible de l'échantillon à analyser.Le bioréacteur parfaitement mélangé se distingue des deux premières méthodes car il travaille théoriquement en consommation totale du substrat. La méthode ne nécessite pas de calibration mais implique, avant toute mesure de respirogramme, la détermination d'un paramètre supplémentaire, le coefficient de transfert de l'oxygène.De manière générale, la principale conclusion de l'étude réside dans la difficulté de ces appareils à fournir une DO (Demande en oxygène) corrélable à la DBO5 conventionnelle. Leur champ d'application reste en effet limité aux substrats rapidement biodégradables.Leurs potentialités restent cependant conformes aux besoins de contrôle rapide des charges organiques polluantes en entrée et sortie des stations d'épuration.BOD (Biochemical Oxygen Demand) is an important parameter to characterize organic pollution in aquatic environments and sewage. The five-day period required by the classical dilution method (BOD5) is incompatible with real-time control of a sewage treatment plant. Moreover, the assay procedure (closed respirometer, very diluted samples) is not only far from real growing conditions but also far from conditions in sewage treatment plants.Several devices for rapid BOD estimation, all based on respirometric methods, have been developed and tested. These devices can be grouped into 2 categories:- an immobilized biomass plug-flow reactor and a bioelectrode, both based on a flow injection principle; - an immobilized biomass perfectly mixed reactor, based on an open respirometer principle. We have focused mainly on validating the principles, checking the measurement reliability, and defining more precisely the scope of the various devices.The bioelectrodeThe BOD bioelectrode that we developed relies on a classical configuration that uses a yeast strain (Trichosporon cutaneum) as the biological receptor and a Clark probe as the transducer. The main changes made in this system are as follows:- a second biomembraneless Clark probe was added to the 16-ml measuring cell to serve as a reference probe in order to remove experimental disturbances (temperature, oxygen transfer coefficient, dissolved oxygen concentration, etc.). - the second change was to include the respirogram area among the data available for processing. The signal utilized in this set-up is the difference between the signals provided by the two probes. Our conclusions are as follows:- Concerning the signal processing, manufacturers are currently guided by the desire to develop devices able to estimate the BOD of a large range of substrates or effluents in a very short time (a few minutes for the newest devices). However, it seems useful, even necessary in many cases (complex mixtures of components that are oxidized at variable rates), to use information provided by the respirogram shape and area. This approach allows one to maximize the BOD bioelectrode's range for a given immobilized strain, although the trade-off is a longer total run time. - Concerning the adaptation period for microorganisms, it is impossible to correctly estimate BOD from various effluents without first adapting the biomaterial to the type of substrate to be analyzed. Therefore it is dangerous to consider a BOD bioelectrode as an analytical instrument, because an adaptation period is required after any change in the composition or, even more so, type of effluent. - Concerning the correspondence between rapid BOD and BOD5, the BOD sensor can detect only the BOD of soluble compounds that can diffuse through the biomembrane and that will be metabolized during the time of analysis. The difference observed between BOD sensor and BOD5 depends on the calibration solution but also and even more on the structure and size of the molecules constituting the sample to be analyzed. - Concerning the choice of calibration solution, choosing the right calibration solution is crucial. The calibration solution should therefore be qualitatively as close as possible to the test sample. The immobilized biomass bioreactorsThe plug-flow reactorThe plug-flow reactor design was validated for simple substrates; its working principle is similar to the bioelectrodes, since it relies on flow-injection analysis (FIA). In the case of the plug-flow reactor, the only usable information for BOD estimation is the respirogram area, as the peak height quickly reaches a rather constant value due to saturation of the immobilized microorganisms. However, the importance of the many physical and biological processes that occur concomitantly in the system (transfer, adsorption, substrate consumption, substrate saturation phenomena, dilution rate, etc.) makes a theoretical mathematical model of the reactor more difficult to establish. A long-term, more fundamental study of various natural or artificial substrates might ultimately enable us to reach such a goal.On the other hand, a variant of this reactor that recirculates the partially-degraded effluent until it is completely consumed yielded a linear correlation between system response (respirogram area) and substrate amount. In this system, oxidation of the rapidly biodegradable substrates is total under our operating conditions. This alternative reactor seems to have some very interesting possibilities, especially with regard to the automation of the system.The perfectly mixed reactorThe utilization of the perfectly mixed reactor for rapid BOD estimation is based on two sequential experiments - although this has the disadvantage of increasing the total run time - to obtain the respirogram area (S) and oxygen transfer coefficient (KL.a), as the units of the product (KL.a x S) of these parameters are equivalent to those of oxygen demand and their product is the variable that best correlates with the substrate injection volume. This correlation was observed for a large range of substrates. In the case of the perfectly mixed reactor, unlike bioelectrodes,- diffusion processes have no effect on measurement, as the substrate is consumed completely during the experiment; - the substrate consumption rate does not affect the measurements, thereby freeing the method from the influence of various experimental parameters (air flow-rate, the quantity of biomass, the liquid volume in the reactor, etc.), as our tests have shown. For a given substrate, the linearity of the correlation between the product of KL.a x S and the amount of substrate is generally excellent. The attempt to correlate the system's response with the BOD5 measurements for a variety of substrates proved to be difficult, however. Although the bioreactor's analytical range is wider than that of bioelectrodes, the system still fails to give any measurable responses for complex substrates such as starch, cellulose, proteins, etc., and the KL.a x S values estimated by the bioreactor remained much lower than the corresponding BOD5 values. KL.a x S is probably characteristic of the portion of the substrate that is degraded rapidly by the microorganisms to meet their immediate energy needs, whereas the remaining substrate is probably kept for reserve and biomass synthesis

Renormalization group improved gravitational actions: a Brans-Dicke approach

A new framework for exploiting information about the renormalization group (RG) behavior of gravity in a dynamical context is discussed. The Einstein-Hilbert action is RG-improved by replacing Newton's constant and the cosmological constant by scalar functions in the corresponding Lagrangian density. The position dependence of $G$ and $\Lambda$ is governed by a RG equation together with an appropriate identification of RG scales with points in spacetime. The dynamics of the fields $G$ and $\Lambda$ does not admit a Lagrangian description in general. Within the Lagrangian formalism for the gravitational field they have the status of externally prescribed ``background'' fields. The metric satisfies an effective Einstein equation similar to that of Brans-Dicke theory. Its consistency imposes severe constraints on allowed backgrounds. In the new RG-framework, $G$ and $\Lambda$ carry energy and momentum. It is tested in the setting of homogeneous-isotropic cosmology and is compared to alternative approaches where the fields $G$ and $\Lambda$ do not carry gravitating 4-momentum. The fixed point regime of the underlying RG flow is studied in detail.Comment: LaTeX, 72 pages, no figure

Correction to the Casimir force due to the anomalous skin effect

The surface impedance approach is discussed in connection with the precise calculation of the Casimir force between metallic plates. It allows to take into account the nonlocal connection between the current density and electric field inside of metals. In general, a material has to be described by two impedances $Z_{s}(\omega,q)$ and $Z_{p}(\omega,q)$ corresponding to two different polarization states. In contrast with the approximate Leontovich impedance they depend not only on frequency $\omega$ but also on the wave vector along the plate $q$. In this paper only the nonlocal effects happening at frequencies $\omega<\omega_{p}$ (plasma frequency) are analyzed. We refer to all of them as the anomalous skin effect. The impedances are calculated for the propagating and evanescent fields in the Boltzmann approximation. It is found that $Z_p$ significantly deviates from the local impedance as a result of the Thomas-Fermi screening. The nonlocal correction to the Casimir force is calculated at zero temperature. This correction is small but observable at small separations between bodies. The same theory can be used to find more significant nonlocal contribution at $\omega\sim\omega_p$ due to the plasmon excitation.Comment: 29 pages. To appear in Phys. Rev.

Optical measurements of spin noise as a high resolution spectroscopic tool

The intrinsic fluctuations of electron spins in semiconductors and atomic vapors generate a small, randomly-varying "spin noise" that can be detected by sensitive optical methods such as Faraday rotation. Recent studies have demonstrated that the frequency, linewidth, and lineshape of this spin noise directly reveals dynamical spin properties such as dephasing times, relaxation mechanisms and g-factors without perturbing the spins away from equilibrium. Here we demonstrate that spin noise measurements using wavelength-tunable probe light forms the basis of a powerful and novel spectroscopic tool to provide unique information that is fundamentally inaccessible via conventional linear optics. In particular, the wavelength dependence of the detected spin noise power can reveal homogeneous linewidths buried within inhomogeneously-broadened optical spectra, and can resolve overlapping optical transitions belonging to different spin systems. These new possibilities are explored both theoretically and via experiments on spin systems in opposite limits of inhomogeneous broadening (alkali atom vapors and semiconductor quantum dots).Comment: 4 pages, 4 figure

Polypropylene/Layered Double Hydroxide Nanocomposites: Influence of LDH Intralayer Metal Constituents on the Properties of Polypropylene

Sonication-assisted delamination of layered double hydroxides (LDHs) resulted in smaller-sized LDH nanoparticles (∼50-200 nm). Such delaminated Co-Al LDH, Zn-Al LDH, and Co-Zn-Al LDH solutions were used for the preparation of highly dispersed isotactic polypropylene (iPP) nanocomposites. Transmission electron microscopy and wide-angle X-ray diffraction results revealed that the LDH nanoparticles were well dispersed within the iPP matrix. The intention of this study is to understand the influence of the intralayer metal composition of LDH on the various properties of iPP/LDH nanocomposites. The sonicated LDH nanoparticles showed a significant increase in the crystallization rate of iPP; however, not much difference in the crystallization rate of iPP was observed in the presence of different types of LDH. The dynamic mechanical analysis results indicated that the storage modulus of iPP was increased significantly with the addition of LDH. The incorporation of different types of LDH showed no influence on the storage modulus of iPP. But considerable differences were observed in the flame retardancy and thermal stability of iPP with the type of LDH used for the preparation of nanocomposites. The thermal stability (50% weight loss temperature (T0.5)) of the iPP nanocomposite containing three-metal LDH (Co-Zn-Al LDH) is superior to that of the nanocomposites made of two-metal LDH (Co-Al LDH and Zn-Al LDH). Preliminary studies on the flame-retardant properties of iPP/LDH nanocomposites using microscale combustion calorimetry showed that the peak heat release rate was reduced by 39% in the iPP/Co-Zn-Al LDH nanocomposite containing 6 wt % LDH, which is higher than that of the two-metal LDH containing nanocomposites, iPP/Co-Al LDH (24%) and iPP/Zn-Al LDH (31%). These results demonstrated that the nanocomposites prepared using three-metal LDH showed better thermal and flame-retardant properties compared to the nanocomposites prepared using two-metal LDH. This difference might be due to the better char formation capability of three-metal LDH compared to that of two-metal LDH

Tailored quantum dots for entangled photon pair creation

We compare the asymmetry-induced exchange splitting delta_1 of the bright-exciton ground-state doublet in self-assembled (In,Ga)As/GaAs quantum dots, determined by Faraday rotation, with its homogeneous linewidth gamma, obtained from the radiative decay in time-resolved photoluminescence. Post-growth thermal annealing of the dot structures leads to a considerable increase of the homogeneous linewidth, while a strong reduction of the exchange splitting is simultaneously observed. The annealing can be tailored such that delta_1 and gamma become comparable, whereupon the carriers are still well confined. This opens the possibility to observe polarization entangled photon pairs through the biexciton decay cascade.Comment: 4 pages, 4 figure