Showing papers by "Université Paris-Saclay published in 2002"
TL;DR: In this paper, the amplitude of the CP asymmetry is derived from the decay-time distributions in such events, which is consistent with the standard model expectation of no direct CP violation in these modes.
Abstract: We present results on time-dependent CP asymmetries in neutral B decays to several CP eigenstates. The measurements use a data sample of about 88 x 10(6) Upsilon(4S)-->B(-)B decays collected between 1999 and 2002 with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. We study events in which one neutral B meson is fully reconstructed in a final state containing a charmonium meson and the other B meson is determined to be either a B(0) or B(-0) from its decay products. The amplitude of the CP asymmetry, which in the standard model is proportional to sin2beta, is derived from the decay-time distributions in such events. We measure sin2beta=0.741+/-0.067(stat)+/-0.034(syst) and |lambda|=0.948+/-0.051(stat)+/-0.030(syst). The magnitude of lambda is consistent with unity, in agreement with the standard model expectation of no direct CP violation in these modes.
157 citations
TL;DR: In this paper, a stochastic differential equation (SDE) is used to describe stationary "fluid" random evolutions with independent increments, and it is shown that all solutions of the SDE can be obtained by filtering a coalescing motion with respect to a subnoise containing the Gaussian part of its noise.
Abstract: We are interested in stationary "fluid" random evolutions with independent increments. Under some mild assumptions, we show they are solutions of a stochastic differential equation (SDE). There are situations where these evolutions are not described by flows of diffeomorphisms, but by coalescing flows or by flows of probability kernels. In an intermediate phase, for which there exist a coalescing flow and a flow of kernels solution of the SDE, a classification is given: All solutions of the SDE can be obtained by filtering a coalescing motion with respect to a subnoise containing the Gaussian part of its noise. Thus, the coalescing motion cannot be described by a white noise.
152 citations
TL;DR: Using the Wiener chaos decomposition, the authors showed that strong solutions of non-Lipschitzian stochastic differential equations are given by random Markovian kernels.
Abstract: Using the Wiener chaos decomposition, we show that strong solutions of non-Lipschitzian stochastic differential equations are given by random Markovian kernels. The example of Sobolev flows is studied in some detail, exhibiting interesting phase transitions.
151 citations
Journal Article•
TL;DR: It is demonstrated that the NY-ESO-1 119-143 peptide stimulates in vitro both Th1-type and Th2-type CD4+ T-cell responses from peripheral blood lymphocytes of normal donors and melanoma patients.
Abstract: The NY-ESO-1 gene product is expressed by a range of human tumors and is recognized by antibodies from sera of cancer patients with NY-ESO-1-expressing tumors. The NY-ESO-1 gene also encodes several MHC class I- and MHC class II-restricted tumor epitopes recognized by T lymphocytes. In particular, we previously reported that the NY-ESO-1 119–143 peptide contains at least two HLA-DRB1*0401-presented epitopes that are recognized by melanoma-reactive CD4+ T cells. Here we report that the NY-ESO-1 119–143 peptide can be presented in the context of multiple HLA-DR alleles to stimulate tumor-reactive CD4+ T cells. The NY-ESO-1 119–143 peptide is able to bind to several DR molecules. The NY-ESO-1 119–143 peptide is also capable of inducing specific CD4+ T cells in vitro from peripheral blood lymphocytes of normal donors and patients with melanoma who express these HLA-DR alleles. These CD4+ T cells recognize NY-ESO-1+, HLA-matched or autologous melanoma cell lines, as well as autologous antigen-presenting cells fed with the NY-ESO-1 protein. We also demonstrate that the NY-ESO-1 119–143 peptide stimulates in vitro both Th1-type and Th2-type CD4+ T-cell responses from peripheral blood lymphocytes of normal donors and melanoma patients. Taken together, these data suggest a key role of the NY-ESO-1 119–143 peptide sequence in the induction of cellular and humoral responses against NY-ESO-1-expressing tumors. They support the relevance of cancer vaccine trials with the NY-ESO-1 119–143 peptide in the large number of cancer patients with NY-ESO-1-expressing tumors.
121 citations
TL;DR: 4-1BB enhanced expansion, survival and effector functions of newly primed CD8(+) T cells, acting in part directly on these cells, as 4-1 BB agonists may function through these mechanisms to enhance or rescue suboptimal immune responses.
Abstract: Interactions between 4-1BB and its ligand, 4-1BBL, enhance CD8(+) T cell-mediated antiviral and antitumor immunity in vivo. However, mechanisms regulating the priming of CD8(+) T cell responses by 4-1BB remain unclear, particularly in humans. The 4-1BB receptor was undetectable on naive or resting human CD8(+) T cells and induced in vitro by TCR triggering. Naive cord blood cells were therefore primed in vitro against peptides or cellular antigens and then co-stimulated with 4-1BBL or agonistic antibodies. Co-stimulation enhanced effector function such as IFN-gamma production and cytotoxicity by augmenting numbers of antigen-specific and effector CD8(+) T cells. OKT3 responses also showed reduced cell death and revealed that the proliferation of CD8(+) T cells required two independently regulated events. One, the induction of IL-2 production, could be directly triggered by 4-1BB engagement on CD8(+) T cells in the absence of accessory cells. The other, expression of CD25, was induced with variable efficacy by accessory cells. Thus, suboptimal accessory cells and 4-1BB co-stimulation combined their effects to enhance IL-2 production and proliferation. Reduced apoptosis observed after co-stimulation in the presence of accessory cells correlated with increased levels of Bcl-X(L) in CD8(+) T cells, while Bcl-2 expression remained unchanged. Altogether, 4-1BB enhanced expansion, survival and effector functions of newly primed CD8(+) T cells, acting in part directly on these cells. As 4-1BB triggering could be protracted from the TCR signal, 4-1BB agonists may function through these mechanisms to enhance or rescue suboptimal immune responses.
109 citations
University of Michigan1, Carnegie Institution for Science2, Lawrence Berkeley National Laboratory3, University of Washington4, Université Paris-Saclay5, Pontifical Catholic University of Chile6, University of California, Berkeley7, University of Arizona8, Stockholm University9, University of California, Santa Cruz10, University of Oxford11, University of Barcelona12, University of Concepción13, Harvard University14
TL;DR: In this paper, the authors presented the BVRI and JsHKs light curves of SN 1999aw (through ~100 days past maximum light), as well as several epochs of optical spectra.
Abstract: SN 1999aw was discovered during the first campaign of the Nearby Galaxies Supernova Search project. This luminous, slow-declining [Δm15(B) = 0.81 ± 0.03] Type Ia supernova was noteworthy in at least two respects. First, it occurred in an extremely low luminosity host galaxy that was not visible in the template images nor in initial subsequent deep imaging. Second, the photometric and spectral properties of this supernova indicate that it very likely was similar to the subclass of Type Ia supernovae whose prototype is SN 1999aa. This paper presents the BVRI and JsHKs light curves of SN 1999aw (through ~100 days past maximum light), as well as several epochs of optical spectra. From these data, we calculate the bolometric light curve and give estimates of the luminosity at maximum light and the initial 56Ni mass. In addition, we present deep BVI images obtained recently with the Baade 6.5 m telescope at Las Campanas Observatory that reveal the remarkably low-luminosity host galaxy.
92 citations
TL;DR: Theoretical descriptions of the molecular nonlinear optical properties of tetrahedral donor-acceptor molecules were presented by using a valence-bond and four charge-transfer state model as discussed by the authors.
Abstract: Theoretical descriptions of the molecular nonlinear optical properties of tetrahedral donor–acceptor molecules are presented by using a valence-bond and four charge-transfer state model. Based on this five-state model, as the extent of the charge transfer from the peripheral donors (acceptors) to the central acceptor (donor) increases, the first hyperpolarizability monotonically increases. The theoretical predictions are confirmed by carrying out ab initio calculations of the first hyperpolarizabilities of three different series of tetrahedral molecules. The π-electron delocalization effect on the nonlinear optical property is elucidated by making a comparison of the first hyperpolarizability of the tetrahedral molecule with that of fictitious tetrahedrally assembled linear polyynes.
46 citations
TL;DR: This work demonstrates that the spin of the circularly polarized electromagnetic wave can be converted into the angular momentum of the charged particles so long as there is dissipation by considering two mechanisms of angular momentum absorption relevant for laser-plasma interactions: electron-ion collisions and ionization.
Abstract: The interaction between circularly polarized radiation and charged particles can lead to generation of magnetic field through an inverse Faraday effect. The spin of the circularly polarized electromagnetic wave can be converted into the angular momentum of the charged particles so long as there is dissipation. We demonstrate this by considering two mechanisms of angular momentum absorption relevant for laser-plasma interactions: electron-ion collisions and ionization. The precise dissipative mechanism, however, plays a role in determining the efficiency of the magnetic-field generation.
40 citations
TL;DR: In this paper, the authors consider the problem of hard objects on random lattices, and emphasize the crucial role played by the colourability of the lattices to ensure the existence of a crystallization transition.
Abstract: We address the general problem of hard objects on random lattices, and emphasize the crucial role played by the colourability of the lattices to ensure the existence of a crystallization transition. We first solve explicitly the naive (colourless) random-lattice version of the hard-square model and find that the only matter critical point is the non-unitary Lee–Yang edge singularity. We then show how to restore the crystallization transition of the hard-square model by considering the same model on bicoloured random lattices. Solving this model exactly, we show moreover that the crystallization transition point lies in the universality class of the Ising model coupled to 2D quantum gravity. We finally extend our analysis to a new two-particle exclusion model, whose regular lattice version involves hard squares of two different sizes. The exact solution of this model on bicolourable random lattices displays a phase diagram with two (continuous and discontinuous) crystallization transition lines meeting at a higher order critical point, in the universality class of the tricritical Ising model coupled to 2D quantum gravity.
37 citations
TL;DR: Martin et al. as discussed by the authors showed that the relaxation rates of concentration and long-range order fields in substitutional alloys are coupled not only by the driving forces, as they derive from a single free-energy functional, but also by kinetic coefficients, since the very same atomic jumps drive both relaxations.
Abstract: The relaxation rates of concentration and long-range-order fields in substitutional alloys are known to be coupled not only by the driving forces, as they derive from a single free-energy functional, but also by kinetic coefficients, since the very same atomic jumps drive both relaxations. For the simplest kinetic lattice model (the kinetic counterpart of the Bragg-Williams model), the detailed expressions of the coefficients of the appropriate mobility matrix that had been derived previously [G. Martin, Phys. Rev. B 50, 12 362 (1994)] contain two errors, which are corrected in the present paper. Then, using these expressions, we discuss the conditions for the existence of coupling of the relaxation rates of composition and long-range order. In the most general case, where relaxation takes place around an equilibrium state that is inhomogeneous and ordered, the presence of this kinetic coupling is confirmed. In the case where relaxation takes place around a disordered state (homogeneous or inhomogeneous), we show that the mobility matrix reduces to a diagonal form, i.e., that there is no kinetic coupling. In the case of an ordered homogeneous equilibrium state, however, the mobility matrix is found to be symmetrical with off-diagonal terms which do not vanish, in general, although they may vanish for some specific crystallographic structures, or along specific crystallographic directions. It is shown that, near the homogeneous equilibrium state, even in the presence of kinetic coupling, the relaxation rates are such that the free energy of the system decreases monotonically with time, as expected from the second law of thermodynamics. The model is applied to a few ordered structures with cubic or tetragonal symmetry.
35 citations
TL;DR: In this article, the branching fractions of the exclusive decays of the BABAR detector at the PEP II asymmetric $e+}e^{-}$ collider are measured from a sample of $(22.36)-times 10^6$.
Abstract: The branching fractions of the exclusive decays $B^0\to K^{*0}\gamma$ and $B^+ \to K^{*+}\gamma$ are measured from a sample of $(22.74\pm 0.36)\times 10^6$ $B\bar B$ decays collected with the BABAR detector at the PEP II asymmetric $e^{+}e^{-}$ collider. We find ${\cal B}(B^0\to K^{*0}\gamma) = (4.23\pm 0.40({\rm stat.})\pm 0.22({\rm sys.}))\times 10^{-5}$, ${\cal B}(B^+\to K^{*+}\gamma) = (3.83\pm 0.62({\rm stat.})\pm 0.22({\rm sys.}))\times 10^{-5}$ and constrain the CP-violating charge asymmetry to be $-0.170 < A_{CP}(B \to K^*\gamma) < 0.082$ at 90% C.L.
TL;DR: In this article, the authors report branching fraction measurements for exclusive decays of charged and neutral B mesons into two-body final states containing a charmonium meson, using a sample of 22.72 +/- 0.36 million B anti-B events collected between October 1999 and October 2000 with the BABAR detector at the PEP-II storage rings at Stanford Linear Accelerator Center.
Abstract: We report branching fraction measurements for exclusive decays of charged and neutral B mesons into two-body final states containing a charmonium meson. We use a sample of 22.72 +/- 0.36 million B anti-B events collected between October 1999 and October 2000 with the BABAR detector at the PEP-II storage rings at the Stanford Linear Accelerator Center. The charmonium mesons considered here are J/psi, psi(2S), and chi_c1, and the light meson in We report branching fraction measurements for exclusive decays of charged and neutral B mesons into two-body final states containing a charmonium meson. We use a sample of 22.72 +/- 0.36 million B anti-B events collected between October 1999 and October 2000 with the BABAR detector at the PEP-II storage rings at the Stanford Linear Accelerator Center. The charmonium mesons considered here are J/psi, psi(2S), and chi_c1, and the light meson in the decay is either a K, K^*, or pi^0. the decay is either a K, K^*, or pi^0.
TL;DR: In this article, a general inversion formula expressing the partition function of (1 + d)D Lorentzian semi-random lattices with one random (spacelike) direction and d regular (time-like) ones was proposed.
Abstract: We investigate models of (1 + d)D Lorentzian semi-random lattices with one random (space-like) direction and d regular (time-like) ones. We prove a general inversion formula expressing the partition function of these models as the inverse of that of hard objects in d dimensions. This allows for an exact solution of a variety of new models including critical and multicritical generalized (1+1)D Lorentzian surfaces, with fractal dimensions dF = k + 1, k = 1,2,3,... , as well as a new model of (1+2)D critical tetrahedral complexes, with fractal dimension dF = 12/5. Critical exponents and universal scaling functions follow from this solution. We finally establish a general connection between (1 + d)D Lorentzian lattices and directed-site lattice animals in (1 + d) dimensions.
TL;DR: In this article, the results of a search for T, CP, and CPT violation in B^0-B^0 mixing using an inclusive dilepton sample collected by the BABAR experiment at the PEP-II B factory were reported.
Abstract: We report the results of a search for T, CP, and CPT violation in B^0-B^0 mixing using an inclusive dilepton sample collected by the BABAR experiment at the PEP-II B factory. Using a sample of 232×10^6 BB pairs, we measure the T and CP violation parameter |q/p|-1=(-0.8±2.7(stat)±1.9(syst))×10^(-3), and the CPT and CP parameters Imz=(-13.9±7.3(stat)±3.2(syst))×10^(-3) and ΔΓ×Rez=(-7.1±3.9(stat)±2.0(syst))×10^(-3) ps^(-1). The statistical correlation between the measurements of Imz and ΔΓ×Rez is 76%.
TL;DR: Application of a new remote-sensing technique for identifying inundated areas based on the properties of the glitter holds promise for mapping the seasonal and interannual extent of inundation, a key descriptor of wetlands hydrology.
Abstract: Inundation is linked to water, carbon, and energy budgets at landscape to global scales. We describe a new remote-sensing technique for identifying inundated areas based on the properties of the glitter-the strong, angular signature reflection that is characteristic of surface water and uncharacteristic of other cover types. We discriminated three cover types-vegetation emergent above inundated soils, open water, and noninundated cover types-from analysis of directional data collected in the red spectral band by the airborne POLDER (Polarization and Directionality of Earth's Reflectance) sensor. We found that values of the normalized difference vegetation index (NDVI) decreased dramatically in the glitter direction, providing an indication of surface water. Application of our new technique holds promise for mapping the seasonal and interannual extent of inundation, a key descriptor of wetlands hydrology.
TL;DR: Two multidimensional Monte Carlo simulation codes (neutral (H2,H) and negative ion (H−) transport codes) have been developed as discussed by the authors for the H− production in a large, hybrid negative ion source, Camembert III.
Abstract: Two multidimensional Monte Carlo simulation codes—(a) neutral (H2,H) transport code and (b) negative ion (H−) transport code—have been developed. This article focuses on the recent simulation results by the neutral transport code for the H− production in a large, hybrid negative ion source, “Camembert III.” Two-dimensional spatial profiles of vibrationally excited molecules H2(v) and H− production are obtained for a given background plasma profile. Both H2(v) and H− ions are mainly produced near the filaments in the driver region. However, the H− source density has double peak in its spatial structure, while the density profile of H2(v) is characterized by the “mushroom” structure with a single peak. These results indicate a large potential of the neutral transport code, not only for the understanding of underlying physics, but also for designing ion sources, including complicating effects of geometry, spatial and velocity distribution of particles, and atomic and wall processes.
TL;DR: In this paper, the meson production rate from B decays and from qqbar continuum events near the Y(4S) resonance was measured using 20.8 fb-1 of data on the Y 4S resonance and 2.6 fb 1 off resonance, and the inclusive branching fractions were determined from the Ds(*)+ momentum spectra.
Abstract: New measurements of Ds+ and Ds*+ meson production rates from B decays and from qqbar continuum events near the Y(4S) resonance are presented. Using 20.8 fb-1 of data on the Y(4S) resonance and 2.6 fb-1 off resonance, we find the inclusive branching fractions BR(B --> Ds+ X) = (10.93+/-0.19+/-0.58+/-2.73)% and BR(B --> Ds*+ X) = (7.9+/-0.8+/-0.7+/-2.0)%, where the first error is statistical, the second is systematic, and the third is due to the Ds+ --> phi pi+ branching fraction uncertainty. The branching fractions SumBR(B --> Ds(*)+ Dbar(*)) = (5.07+/-0.14+/-0.30+/-1.27)% and SumBR(B --> Ds*+ Dbar(*)) = (4.1+/-0.2+/-0.4+/-1.0)% are determined from the Ds(*)+ momentum spectra.
01 Mar 2002
TL;DR: In this paper, an approach for calculating K → ππ decays to the next-to-leading order in chiral expansion is proposed, and a detailed numerical study of this approach is performed.
Abstract: We propose an approach for calculating K → ππ decays to the next-to-leading order in chiral expansion. A detailed numerical study of this approach is being performed.
TL;DR: In this article, the B{sup {+-}} {yields} J/{psi}{pi} K{sup ] decays using a 20.7 fb{sup -1} data set collected with the BABAR detector.
Abstract: We have studied the B{sup {+-}} {yields} J/{psi}{pi}{sup {+-}} and B{sup {+-}} {yields} J/{psi} K{sup {+-}} decays using a 20.7 fb{sup -1} data set collected with the BABAR detector. We observe a signal of 51 {+-} 10 B{sup {+-}} {yields} J/{psi}{pi}{sup {+-}} events and determine the ratio {Beta}(B{sup {+-}} {yields} J/{psi}{pi}{sup {+-}})/{Beta}(B{sup {+-}} {yields} J/{psi} K{sup {+-}}) to be [3.91 {+-} 0.78(stat.) {+-} 0.19(syst.)]%. The CP-violating charge asymmetries for the B{sup {+-}} {yields} J/{psi} {pi}{sup {+-}} and B{sup {+-}} {yields} J/{psi} K{sup {+-}} decays are determined to be {Alpha}{sub {pi}} = 0.01 {+-} 0.22(stat.) {+-} 0.01(syst.) and {Alpha}{sub K} = 0.003 {+-} 0.030(stat.) {+-} 0.004(syst.).
TL;DR: In this article, the authors search for direct CP violation in charmless hadronic B decays observed in a sample of about 22.7 million B (B) over bar pairs collected with the BABAR detector at the SLAC PEP-II asymmetric-energy e(+)e(-) collider.
Abstract: We search for direct CP violation in charmless hadronic B decays observed in a sample of about 22.7 million B (B) over bar pairs collected with the BABAR detector at the SLAC PEP-II asymmetric-energy e(+)e(-) collider. We measure the following charge asymmetries: A(CP)(B+/- --> eta'K+/-) = -0.11 +/- 0.11 +/- 0.02, A(CP)(B+/- --> omegapi+/-) = -0.01 +/- (0.29)(0.31) +/- 0.03, A(CP)(B+/- -->phiK+/-)= -00.5 +/-0.20+/-0.03, A(CP)(B+/- --> phiK*=/-)= -0.43 (+0.36)(-0.30) +/-0.06, and A(CP)((B) over bar (0) --> phi(K) over bar*(0)) = 0.00 +/- 0.27 +/- 0.03.
TL;DR: In this paper, a search for pair-produced charged Higgs bosons was performed in the high energy data collected by the DELPHI detector at LEP II at center-of-mass energies from 189 ~GeV to 202~GeV\@.
TL;DR: In this article, a search for evidence of minimal supergravity (MSUGRA) in 92.7 pb(-1) of data collected with the D empty set detector at the Fermilab Tevatron p (p) over bar collider at roots=1.8 TeV was described.
Abstract: We describe a search for evidence of minimal supergravity (MSUGRA) in 92.7 pb(-1) of data collected with the D empty set detector at the Fermilab Tevatron p (p) over bar collider at roots=1.8 TeV. Events with a single electron, four or more jets, and large missing transverse energy were used in this search. The major backgrounds are from W+jets, misidentified multijet, t (t) over bar, and WW production. We observe no excess above the expected number of background events in our data. A new limit in terms of MSUGRA model parameters is obtained.
Journal Article•
TL;DR: In this paper, interference stabilization of diatomic molecules with respect to their photodissociation by a strong laser field is considered, where multiple strong-field-induced Raman-type transitions between vibrational levels of the ground electronic state are taken into account.
Abstract: Interference stabilization of diatomic molecules with respect to their photodissociation by a strong laser field is considered. Multiple strong-field-induced Raman-type transitions between vibrational levels of the ground electronic state are taken into account. For the molecular ion H + 2 matrix elements of these transitions are calculated, the arising equations are solved numerically, and the time-dependent probability amplitudes to find a molecule at ground-electronic-state vibrational levels are found. In a stationary formulation, complex quasienergies are found and analyzed. At some specific values of the light frequency some quasienergy zones are shown to narrow with growing light intensity, and this effect is related directly to the field-induced stabilization. In solution of the initial-value problem, the total probability of photodissociation per pulse is shown to decrease its growth with growing peak light intensity. Investigation of frequency-dependence of the photodissociation yield is used to determine stabilization conditions and to clarify the physical origin of the effect.
18 Jan 2002
TL;DR: In this article, two mechanisms of angular momentum absorption relevant for laser-plasma interactions were considered, namely electron-ion collisions and ionization, and the precise dissipative mechanism played a role in determining the efficiency of the magnetic field generation.
Abstract: The interaction between circularly polarized (CP) radiation and charged particles can lead to generation of magnetic field through an inverse Faraday effect. The spin of the circularly polarized electromagnetic wave can be converted into the angular momentum of the charged particles so long as there is dissipation. We demonstrate this by considering two mechanisms of angular momentum absorption relevant for laser-plasma interactions: electron-ion collisions and ionization. The precise dissipative mechanism, however, plays a role in determining the efficiency of the magnetic field generation.
TL;DR: For a few months around perihelion, the central part of the Hale-Bopp hydrogen cloud has been optically thick to the solar Lyα radiation, and has significantly reduced the solar flux available for the resonance glow of interstellar hydrogen beyond the comet.
Abstract: For a few months around perihelion, the central part of the Hale-Bopp hydrogen cloud has been optically thick to the solar Lyα radiation, and has significantly reduced the solar flux available for the resonance glow of interstellar hydrogen beyond the comet. This shadowing effect on the interstellar gas is the first ever observed comet shadow. It is modeled and compared with SWAN observations. Shadow modelling will help to constrain the comet water production and radiative transfer effects in the interstellar ionisation cavity.
Journal Article•
TL;DR: In this article, the 3D models are automatically computed from the original video sequence, where the camera parameters and the scene content are unknown and the video sequence is processed on the fly.
Abstract: This paper presents new results in the field of very low bitrate codir~g and cornpression usirig 3D iriforrnations. Contrary to prior art in model-based coding where 3D models have to be known, the 3D models are automatically computed from the original video sequence. The camera parameters and the scene content are supposed unknown and the video sequence is processed on the fly. A stream of 3D models is then extracted and compressed, using adapted compression techniques. \Ve finally show results of the proposed compression scheme, and show the efficiency of these approach.
01 Jan 2002
01 Jan 2002
TL;DR: In this paper, Tangthieng et al. presented experimental results concerning the solidification of a binary aqueous solution, where forced convection in the liquid phase is assumed to dominate over possible natural convection at the interface and the influence of the initial solute concentration is analyzed.
Abstract: This paper presents experimental results concerning the solidification of a binary aqueous solution flowing along acold surface. Forced convection in the liquid phase is assumed to dominate over possible natural convection effects atthe interface and the influence of the initial solute concentration is analyzed. Solute rejection at the interface is shown toinfluence the equilibrium temperature at the solidification front and the time evolution of the solid phase. Comparisonwith the numerical solution of a simple thermal phase change model shows that the solidification dynamics is com-patible with a porous structure of the solid phase (solid fraction about 0.90), accounting for dendritic structure at themicroscale. 2003 Elsevier Ltd. All rights reserved.1. IntroductionSolidification of binary alloys has been the subject ofmany studies in recent years. The presence of naturalconvection due to the phase change process itself isknown to have a strong influence on the dynamics of theprocess, as reported by Davis et al. [1] or experimentallystudied by Prescott and Incropera [2] or Tanny [3]. Dueto the combined temperature and composition gradi-ents, solidification along a flat plate is affected by doublediffusive instabilities (horizontal plate) or thermosolutalconvection (vertical plate), both in terms of solidificationrate and of mush structure. Many experiments, modelsand stability studies have been dedicated to this problemin the heat transfer literature in order to characterize thecomplex interaction between the flow structure and thedynamics of the interfacial growth region. Otherwise,many studies have dealt with features of water–ice in-terface in external or internal forced flow during freezingor melting processes, as referred by Epstein and Cheung[4], but very few studies are concerned with binarysubstances. The existing studies deal with the effect of animposed shear flow on the stability of directional solid-ification of binary alloys and are investigated by theo-retical or numerical approach (Forth and Wheeler [5,6],Chung and Chen [7] and very recently Tangthieng andCheung [8]).The purpose of the present work is to partially un-couple the heat and mass transfer mechanisms at a so-lidifying interface, by limiting the effects of naturalconvection on the phase change process. In oppositionto the usual practice where natural convection is inhib-ited to impose a purely diffusive heat and speciestransfer, the present approach aims at imposing a forcedflow at the solid–liquid interface. Thus, the influence of aconvective flow at the interface is retained, but there isno (or little) feedback of the interface structure anddynamics on the flow itself. More precisely, the scope ofthis paper is to experimentally tackle the problem ofsolidification of a binary mixture along a horizontal flatplate in a forced laminar flow. Under moderate Rey-nolds number laminar shear flow conditions, the heatand species transfer at the growing interface is domi-nated by the forced flow, although gravity effects may bedetected when considering growth either from the top orfrom the bottom surface of the plate.Accurate local temperature measurements of the topinterface have been performed. Local thermodynamicequilibrium being assumed, those temperature mea-surements provide experimental values for the localfront concentration and point out the importance of