Admixture of an s-wave component to the d-wave gap symmetry in high-temperature superconductors

Neutron crystal-field spectroscopy experiments in the Y- and La-type high-temperature superconductors HoBa2Cu3O6.56, HoBa2Cu4O8, and La1.81Sr0.15Ho0.04CuO4 are reviewed. By this bulk-sensitive technique, information on the gap function is obtained from the relaxation behavior of crystal-field transitions associated with the Ho3+ ions which sit as local probes close to the superconducting copper-oxide planes. The relaxation data exhibit a peculiar change from a convex to a concave shape between the superconducting transition temperature Tc and the pseudogap temperature T* which can only be modelled satisfactorily if the gap function of predominantly d-wave symmetry includes an s-wave component of the order of 20-25%, independent of the doping level. Moreover, our results are compatible with an unusual temperature dependence of the gap function in the pseudogap region (Tc<T<T*), i.e., a breakup of the Fermi surface into disconnected arcs.Comment: 14 pages, 3 figures, 1 table; accepted for publication in J. Supercond. Nov. Mag

Laminar drag reduction in surfactant-contaminated superhydrophobic channels

While superhydrophobic surfaces (SHSs) show promise for drag reduction applications, their performance can be compromised by traces of surfactant, which generate Marangoni stresses that increase drag. This question is addressed for soluble surfactant in a three-dimensional laminar channel flow, with periodic SHSs on both walls. We assume that diffusion is sufficiently strong for cross-channel concentration gradients to be small. Exploiting a long-wave theory that accounts for a rapid transverse Marangoni-driven flow, we derive a one-dimensional model for surfactant evolution, which allows us to predict the drag reduction across the parameter space. The system exhibits multiple regimes, involving competition between Marangoni effects, bulk and interfacial diffusion, advection and shear dispersion. We map out asymptotic regions in the high-dimensional parameter space, deriving approximations of the drag reduction in each region and comparing them to numerical simulations. Our atlas of maps provides a comprehensive analytical guide for designing surfactant-contaminated channels with SHSs, to maximise the drag reduction in applications

Unsteady evolution of slip and drag in surfactant-contaminated superhydrophobic channels

Recognising that surfactants may impede the drag reduction resulting from superhydrophobic surfaces (SHSs), and that surfactant concentrations can fluctuate in space and time, we examine the unsteady transport of soluble surfactant in a laminar pressure-driven channel flow bounded between two SHSs. The SHSs are periodic in the streamwise and spanwise directions. We assume that the channel length is much longer than the streamwise period, the streamwise period is much longer than the channel height and spanwise period, and bulk diffusion is sufficiently strong for cross-channel concentration gradients to be small. By combining long-wave and homogenisation theories, we derive an unsteady advection-diffusion equation for surfactant flux transport over the length of the channel, which is coupled to a quasi-steady advection-diffusion equation for surfactant transport over individual plastrons. As diffusion over the length of the channel is typically small, the leading-order surfactant flux is governed by a nonlinear advection equation that we solve using the method of characteristics. We predict the propagation speed of a bolus of surfactant and describe its nonlinear evolution via interaction with the SHS. The propagation speed can fall significantly below the average streamwise velocity as the surfactant adsorbs and rigidifies the plastrons. Smaller concentrations of surfactant are therefore advected faster than larger ones, so that wave-steepening effects can lead to shock formation in the surfactant-flux distribution. These findings reveal the spatio-temporal evolution of the slip velocity and enable prediction of the dynamic drag reduction and effective slip length in microchannel applications

Dynamical charge inhomogeneity and crystal-field fluctuations for 4f ions in high-Tc cuprates

The main relaxation mechanism of crystal-field excitations in rare-earth ions in cuprates is believed to be provided by the fluctuations of crystalline electric field induced by a dynamic charge inhomogeneity generic for the doped cuprates. We address the generalized granular model as one of the model scenario for such an ingomogeneity where the cuprate charge subsystem remind that of Wigner crystal with the melting transition and phonon-like positional excitation modes. Formal description of R-ion relaxation coincides with that of recently suggested magnetoelastic mechanism.Comment: 4 page

Poor screening and nonadiabatic superconductivity in correlated systems

In this paper we investigate the role of the electronic correlation on the hole doping dependence of electron-phonon and superconducting properties of cuprates. We introduce a simple analytical expression for the one-particle Green's function in the presence of electronic correlation and we evaluate the reduction of the screening properties as the electronic correlation increases by approaching half-filling. The poor screening properties play an important role within the context of the nonadiabatic theory of superconductivity. We show that a consistent inclusion of the reduced screening properties in the nonadiabatic theory can account in a natural way for the $T_c$-$\delta$ phase diagram of cuprates. Experimental evidences are also discussed.Comment: 12 Pages, 6 Figures, Accepted on Physical Review

Pseudogap behavior of nuclear spin relaxation in high Tc superconductors in terms of phase separation

We analyze anew experiments on the NMR in cuprates and find an important information on their phase separation and its stripe character hidden in the dependence of $1/^{63}T_{1}$ on degree of doping. In a broad class of materials $1/^{63}T_{1}$ is the sum of two terms: the temperature independent one attributed to ``incommensurate'' stripes that occur at external doping, and an ``universal'' temperature dependent term ascribed to moving metallic and AF sub-phases. We argue that the frustrated first order phase transition in a broad temperature interval bears a dynamical character.Comment: 5 pages, 3 figures; some comments and references added; accepted for publication in JETP Letter

Extracellular Vesicles Enriched in Connexin 43 Promote a Senescent Phenotype in Bone and Synovial Cells Contributing to Osteoarthritis Progression

[Abstract] The accumulation of senescent cells is a key characteristic of aging, leading to the progression of age-related diseases such as osteoarthritis (OA). Previous data from our laboratory has demonstrated that high levels of the transmembrane protein connexin 43 (Cx43) are associated with a senescent phenotype in chondrocytes from osteoarthritic cartilage. OA has been reclassified as a musculoskeletal disease characterized by the breakdown of the articular cartilage affecting the whole joint, subchondral bone, synovium, ligaments, tendons and muscles. However, the mechanisms that contribute to the spread of pathogenic factors throughout the joint tissues are still unknown. Here, we show for the first time that small extracellular vesicles (sEVs) released by human OA-derived chondrocytes contain high levels of Cx43 and induce a senescent phenotype in targeted chondrocytes, synovial and bone cells contributing to the formation of an inflammatory and degenerative joint environment by the secretion of senescence-associated secretory associated phenotype (SASP) molecules, including IL-1ß and IL-6 and MMPs. The enrichment of Cx43 changes the protein profile and activity of the secreted sEVs. Our results indicate a dual role for sEVs containing Cx43 inducing senescence and activating cellular plasticity in target cells mediated by NF-kß and the extracellular signal-regulated kinase 1/2 (ERK1/2), inducing epithelial-to-mesenchymal transition (EMT) signalling programme and contributing to the loss of the fully differentiated phenotype. Our results demonstrated that Cx43-sEVs released by OA-derived chondrocytes spread senescence, inflammation and reprogramming factors involved in wound healing failure to neighbouring tissues, contributing to the progression of the disease among cartilage, synovium, and bone and probably from one joint to another. These results highlight the importance for future studies to consider sEVs positive for Cx43 as a new biomarker of disease progression and new target to treat OA.This work was supported in part through funding from Health Institute ‘Carlos III’ (ISCIII, Spain), the European Regional Development Fund, ‘A way of making Europe’ from the European Union (to MDM): grant PI19/00145; a grant from the Joint Transnational Call for Proposals for “European Innovative Research & Technological Development Projects in Nanomedicine” EURONANOMED III (AC21_2/00026) (to MDM); a grant from Xunta de Galicia (IN607B2020/12) (to MDM) and from H2020, Future and Emerging Technologies (grant 858014 “PANACHE”) to MDM. MV-E was funded with a predoctoral (ED481A-2015/188) and post-doctoral fellowship (IN606B-2019/004) from Xunta de Galicia. AG-C was funded with a predoctoral fellowship (FIS20/00310) from ISCIII. PC-F was funded with a post-doctoral fellowship and a grant from Xunta de Galicia (INB606B 2017/014 and IN606C 2021/006). We thank members of the CellCOM group for helpful technical suggestion, María Dolores Álvarez Alvariño (CHUS) for generously collecting tissue samples in the operating room after surgery and Arantxa Tabernero (INCYL, University of Salamanca) for kindly providing the human Cx43 plasmid used in this studyXunta de Galicia; IN607B2020/12Xunta de Galicia; ED481A-2015/188Xunta de Galicia; IN606B-2019/004Xunta de Galicia; INB606B 2017/014Xunta de Galicia; IN606C 2021/00

Stripes, Vibrations and Superconductivity

We propose a model of a spatially modulated collective charge state of superconducting cuprates. The regions of higher carrier density (stripes) are described in terms of Luttinger liquids and the regions of lower density as a two-dimensional interacting bosonic gas of d_{x^2-y^2} hole pairs. The interactions among the elementary excitations are repulsive and the transition to the superconducting state is driven by decay processes. Vibrations of the CCS and the lattice, although not participating directly in the binding mechanism, are fundamental for superconductivity. The superfluid density and the lattice have a strong tendency to modulation implying a still unobserved dimerized stripe phase in cuprates. The phase diagram of the model has a crossover from 1D to 2D behavior and a pseudogap region where the amplitude of the order parameters are finite but phase coherence is not established. We discuss the nature of the spin fluctuations and the unusual isotope effect within the model.Comment: 51 pages, 20 figures. Post-March Meeting version: New references are added, some of the typos are corrected, and a few new discussions are include

A Theory for High-TcT_c Superconductors Considering Inhomogeneous Charge Distribution

We propose a general theory for the critical $T_c$ and pseudogap $T^*$ temperature dependence on the doping concentration for high-$T_c$ oxides, taking into account the charge inhomogeneities in the $CuO_2$ planes. The well measured experimental inhomogeneous charge density in a given compound is assumed to produce a spatial distribution of local $\rho(r)$. These differences in the local charge concentration is assumed to yield insulator and metallic regions, possibly in a stripe morphology. In the metallic region, the inhomogeneous charge density yields also spatial distributions of superconducting critical temperatures $T_c(r)$ and zero temperature gap $\Delta_0(r)$. For a given sample, the measured onset of vanishing gap temperature is identified as the pseudogap temperature, that is, $T^*$, which is the maximum of all $T_c(r)$. Below $T^*$, due to the distribution of $T_c(r)$'s, there are some superconducting regions surrounded by insulator or metallic medium. The transition to a superconducting state corresponds to the percolation threshold among the superconducting regions with different $T_c(r)$'s. To model the charge inhomogeneities we use a double branched Poisson-Gaussian distribution. To make definite calculations and compare with the experimental results, we derive phase diagrams for the BSCO, LSCO and YBCO families, with a mean field theory for superconductivity using an extended Hubbard Hamiltonian. We show also that this novel approach provides new insights on several experimental features of high-$T_c$ oxides.Comment: 7 pages, 5 eps figures, corrected typo

A Trial of Early Antiretrovirals and Isoniazid Preventive Therapy in Africa

BACKGROUND: In sub-Saharan Africa, the burden of human immunodeficiency virus (HIV)-associated tuberculosis is high. We conducted a trial with a 2-by-2 factorial design to assess the benefits of early antiretroviral therapy (ART), 6-month isoniazid preventive therapy (IPT), or both among HIV-infected adults with high CD4+ cell counts in Ivory Coast. METHODS: We included participants who had HIV type 1 infection and a CD4+ count of less than 800 cells per cubic millimeter and who met no criteria for starting ART according to World Health Organization (WHO) guidelines. Participants were randomly assigned to one of four treatment groups: deferred ART (ART initiation according to WHO criteria), deferred ART plus IPT, early ART (immediate ART initiation), or early ART plus IPT. The primary end point was a composite of diseases included in the case definition of the acquired immunodeficiency syndrome (AIDS), non-AIDS-defining cancer, non-AIDS-defining invasive bacterial disease, or death from any cause at 30 months. We used Cox proportional models to compare outcomes between the deferred-ART and early-ART strategies and between the IPT and no-IPT strategies. RESULTS: A total of 2056 patients (41% with a baseline CD4+ count of ≥500 cells per cubic millimeter) were followed for 4757 patient-years. A total of 204 primary end-point events were observed (3.8 events per 100 person-years; 95% confidence interval [CI], 3.3 to 4.4), including 68 in patients with a baseline CD4+ count of at least 500 cells per cubic millimeter (3.2 events per 100 person-years; 95% CI, 2.4 to 4.0). Tuberculosis and invasive bacterial diseases accounted for 42% and 27% of primary end-point events, respectively. The risk of death or severe HIV-related illness was lower with early ART than with deferred ART (adjusted hazard ratio, 0.56; 95% CI, 0.41 to 0.76; adjusted hazard ratio among patients with a baseline CD4+ count of ≥500 cells per cubic millimeter, 0.56; 95% CI, 0.33 to 0.94) and lower with IPT than with no IPT (adjusted hazard ratio, 0.65; 95% CI, 0.48 to 0.88; adjusted hazard ratio among patients with a baseline CD4+ count of ≥500 cells per cubic millimeter, 0.61; 95% CI, 0.36 to 1.01). The 30-month probability of grade 3 or 4 adverse events did not differ significantly among the strategies. CONCLUSIONS: In this African country, immediate ART and 6 months of IPT independently led to lower rates of severe illness than did deferred ART and no IPT, both overall and among patients with CD4+ counts of at least 500 cells per cubic millimeter. (Funded by the French National Agency for Research on AIDS and Viral Hepatitis; TEMPRANO ANRS 12136 ClinicalTrials.gov number, NCT00495651.)