Effects of wall compliance on the laminar–turbulent transition of torsional Couette flow

Torsional Couette flow between a rotating disk and a stationary wall is studied experimentally. The surface of the disk is either rigid or covered with a compliant coating. The influence of wall compliance on characteristic flow instabilities and on the laminar–turbulent flow transition is investigated. Data obtained from analysing flow visualizations are discussed. It is found that wall compliance favours two of the three characteristic wave patterns associated with the transition process and broadens the parameter regime in which these patterns are observed. The results for the effects of wall compliance on the third pattern are inconclusive. However, the experiments indicate that the third pattern is not a primary constituent of the laminar–turbulent transition process of torsional Couette flow

Creep via dynamical functional renormalization group

We study a D-dimensional interface driven in a disordered medium. We derive finite temperature and velocity functional renormalization group (FRG) equations, valid in a 4-D expansion. These equations allow in principle for a complete study of the the velocity versus applied force characteristics. We focus here on the creep regime at finite temperature and small velocity. We show how our FRG approach gives the form of the v-f characteristics in this regime, and in particular the creep exponent, obtained previously only through phenomenological scaling arguments.Comment: 4 pages, 3 figures, RevTe

Numerical simulation evidence of dynamical transverse Meissner effect and moving Bose glass phase

We present 3D numerical simulation results of moving vortex lattices in presence of 1D correlated disorder at zero temperature. Our results with field tilting confirm the theoritical predictions of a moving Bose glass phase, characterized by transverse pinning and dynamical transverse Meissner effect, the moving flux lines being localized along the correlated disorder direction. Beyond a critical transverse field, vortex lines exhibit along all their length a "kink" structure resulting from an effective static "tin roof" pinning potential in the transverse direction.Comment: 5 pages, 4 figure

Minimal Conflicting Sets for the Consecutive Ones Property in ancestral genome reconstruction

A binary matrix has the Consecutive Ones Property (C1P) if its columns can be ordered in such a way that all 1's on each row are consecutive. A Minimal Conflicting Set is a set of rows that does not have the C1P, but every proper subset has the C1P. Such submatrices have been considered in comparative genomics applications, but very little is known about their combinatorial structure and efficient algorithms to compute them. We first describe an algorithm that detects rows that belong to Minimal Conflicting Sets. This algorithm has a polynomial time complexity when the number of 1's in each row of the considered matrix is bounded by a constant. Next, we show that the problem of computing all Minimal Conflicting Sets can be reduced to the joint generation of all minimal true clauses and maximal false clauses for some monotone boolean function. We use these methods on simulated data related to ancestral genome reconstruction to show that computing Minimal Conflicting Set is useful in discriminating between true positive and false positive ancestral syntenies. We also study a dataset of yeast genomes and address the reliability of an ancestral genome proposal of the Saccahromycetaceae yeasts.Comment: 20 pages, 3 figure

The depinning transition of a driven interface in the random-field Ising model around the upper critical dimension

We investigate the depinning transition for driven interfaces in the random-field Ising model for various dimensions. We consider the order parameter as a function of the control parameter (driving field) and examine the effect of thermal fluctuations. Although thermal fluctuations drive the system away from criticality the order parameter obeys a certain scaling law for sufficiently low temperatures and the corresponding exponents are determined. Our results suggest that the so-called upper critical dimension of the depinning transition is five and that the systems belongs to the universality class of the quenched Edward-Wilkinson equation.Comment: accepted for publication in Phys. Rev.

2-loop Functional Renormalization for elastic manifolds pinned by disorder in N dimensions

We study elastic manifolds in a N-dimensional random potential using functional RG. We extend to N>1 our previous construction of a field theory renormalizable to two loops. For isotropic disorder with O(N) symmetry we obtain the fixed point and roughness exponent to next order in epsilon=4-d, where d is the internal dimension of the manifold. Extrapolation to the directed polymer limit d=1 allows some handle on the strong coupling phase of the equivalent N-dimensional KPZ growth equation, and eventually suggests an upper critical dimension of about 2.5.Comment: 4 pages, 3 figure

Apports des traçages artificiel et naturel à la connaissance des circulations et des zones de recharge en région semi-aride: cas de l'Atlas de Beni Mellal (Maroc)

Pour mieux comprendre les modalités d'alimentation des sources de l'Atlas, des campagnes de coloration et d'analyses isotopiques ont été effectuées sur l'ensemble des sources. La disparité des circulations, la variabilité des vitesses et des taux de restitution, révèlent un aquifère complexe ou à plusieurs entrées. La majorité des écoulements convergent vers la source de Ain Asserdoune qui constitue une zone d'abaissement d'axe de plis. L'étude isotopique montre la variation des teneurs en 180 avec l'altitude des zones de recharge des différents exutoires et avec la saison. Les gradients définis autorisent la détermination de l'altitude moyenne des impluviums des systèmes jusqu'alors mal connus, en particulier celui de l'exutoire principal du massif, Ain Asserdoune.The chalky massif of Beni-Mellal, which supplies many springs, spreads over a 365 km2 area of 500 to 2400 meters elevation (average altitude, 1200 m). Rainfall in this sector varies between 400 mm and 700 mm/year. All springs emerge along the major coastal fault giving the Liassic massif overthrushing the Cenozoic lands of piemont. The most important is Ain Asserdoune spring with an average discharge of about 1.1 m3/s. The mainly chalky and dolomitic formations are very fractured according to preferential directions (N150-180 and N50-70) and show some karstification features at the surface. Some tracing experiments with fluorescein allowed the delimitation of the boundaries of the intake area of Ain Asserdoune Basin and the determination of the groundwater flow velocity. Two types of flow were identified with fast (100 to 231 m/h) and slow circulation (< 100 m/h). Most of circulations converge towards the spring of Ain Asserdoune (fig. 1) with an important intake area. This convergence results from an axis lowering. The variability of the circulation axes, the velocity and the rate of restitution suggest either a complex aquifer or an aquifer with several inputs.Two water samplings (the first for the Beni Mellal Atlas) were carriet out in March and in September 1993 on the several springs, in order to study the variations of the oxygen-18 isotope. The oxygen-18 contents range between - 5.5 per thousand and - 7.7 per thousand (table 2). The most depleted waters directly exit from the Liassic aquifer or emerge at high altitudes; those which are richer in oxygen-18 emerge at the level of foothills, either from the Tertiary or from Liassic scales. The relationship between the oxygen-18 and the H-2 content of some samples indicates that the points are aligned along the world meteoric line (Craig, 1961). Even if the waters of Dir (piemont) springs are slighly evaporated because they partly originate in seeping Liassic waters, oxygen-18 content is probably mainly controlled by an altitude effect. Oxygen-18 data for local precipitations are not available; however, a local relationship between oxygen-18 content and mean recharge altitude was etablished for eleven (11) springs with small recharge areas whose mean altitude may be estimated from topography and geology. Oxygen 18 ratio is very well correlated to recharge average elevation for spring samples ( [delta]per thousand (O - 18)=- 3 - 0,0026 x altitude, r=0,96, fig. 3), when it is not for autumn samples. This gradient is very close to the regional relationship proposed by Marce (1975) and Kabbaj et al. (1978) (slope: 3 per thousand in oxygen-18 per 1,000 m ). This difference is attributed to the seasonal variations in the origin of water that feeds the springs. In the high water season, the whole basin area contributes to the recharge. In contrast, during low water period, water mainly originates from altitudes higher than the mean altitude of the basin, probably with a longer transit time. The seasonal variations are particularly marked for the Dir (piemont) springs (with a lower flux and intake area range of 800 to 1,200 m). They are weaker for the Lias springs and even non-existent for the main spring of the massif, Ain Asserdoune. In this latter case, the smoothing (- 7.6 per thousand and - 7.5 per thousand) of seasonal variation (which is also observed for temperature: 15.5 to 16°C ) gives evidence of important water reserves. A mean recharge altitude higher than 1,700 m may be proposed for Ain Asseroune. Based on this analysis, some emergences which in the part were assigned to the same hydrologic system can now be discriminated. On the other hand, with a similar value of oxygen-18 ratio, rather distant springs can be considered as belonging to the same hydrogeological Atlasic unit. So the relationship which was quantified (slope: 2.6 per thousand in oxygen-18 per 1,000 m) is usable for the whole Atlasic range on account of regionaly similar weather. The methodology selected in this work corroborates the results obtained by hydrometric analysis concerning the very important groundwater reserves in the Beni Mellal aquifer

Drift of a polymer chain in disordered media

We consider the drift of a polymer chain in a disordered medium, which is caused by a constant force applied to the one end of the polymer, under neglecting the thermal fluctuations. In the lowest order of the perturbation theory we have computed the transversal fluctuations of the centre of mass of the polymer, the transversal and the longitudinal size of the polymer, and the average velocity of the polymer. The corrections to the quantities under consideration, which are due to the interplay between the motion and the quenched forces, are controlled by the driving force and the degree of polymerization. The transversal fluctuations of the Brownian particle and of the centre of mass of the polymer are obtained to be diffusive. The transversal fluctuations studied in the present Letter may also be of relevance for the related problem of the drift of a directed polymer in disordered media and its applications.Comment: 11 pages, RevTex, Accepted for publication in Europhysics Letter

2-loop Functional Renormalization Group Theory of the Depinning Transition

We construct the field theory which describes the universal properties of the quasi-static isotropic depinning transition for interfaces and elastic periodic systems at zero temperature, taking properly into account the non-analytic form of the dynamical action. This cures the inability of the 1-loop flow-equations to distinguish between statics and quasi-static depinning, and thus to account for the irreversibility of the latter. We prove two-loop renormalizability, obtain the 2-loop beta-function and show the generation of "irreversible" anomalous terms, originating from the non-analytic nature of the theory, which cause the statics and driven dynamics to differ at 2-loop order. We obtain the roughness exponent zeta and dynamical exponent z to order epsilon^2. This allows to test several previous conjectures made on the basis of the 1-loop result. First it demonstrates that random-field disorder does indeed attract all disorder of shorter range. It also shows that the conjecture zeta=epsilon/3 is incorrect, and allows to compute the violations, as zeta=epsilon/3 (1 + 0.14331 epsilon), epsilon=4-d. This solves a longstanding discrepancy with simulations. For long-range elasticity it yields zeta=epsilon/3 (1 + 0.39735 epsilon), epsilon=2-d (vs. the standard prediction zeta=1/3 for d=1), in reasonable agreement with the most recent simulations. The high value of zeta approximately 0.5 found in experiments both on the contact line depinning of liquid Helium and on slow crack fronts is discussed.Comment: 32 pages, 17 figures, revtex