Liquid-phase exfoliation of bismuth telluride iodide (BiTeI): structural and optical properties of single-/few-layer flakes

Bismuth telluride halides (BiTeX) are Rashba-type crystals with several potential applications ranging from spintronics and nonlinear optics to energy. Their layered structures and low cleavage energies allow their production in a two-dimensional form, opening the path to miniaturized device concepts. The possibility to exfoliate bulk BiTeX crystals in the liquid represents a useful tool to formulate a large variety of functional inks for large-scale and cost-effective device manufacturing. Nevertheless, the exfoliation of BiTeI by means of mechanical and electrochemical exfoliation proved to be challenging. In this work, we report the first ultrasonication-assisted liquid-phase exfoliation (LPE) of BiTeI crystals. By screening solvents with different surface tension and Hildebrandt parameters, we maximize the exfoliation efficiency by minimizing the Gibbs free energy of the mixture solvent/BiTeI crystal. The most effective solvents for the BiTeI exfoliation have a surface tension close to 28 mN m(-1) and a Hildebrandt parameter between 19 and 25 MPa0.5. The morphological, structural, and chemical properties of the LPE-produced single-/few-layer BiTeI flakes (average thickness of & SIM;3 nm) are evaluated through microscopic and optical characterizations, confirming their crystallinity. Second-harmonic generation measurements confirm the non-centrosymmetric structure of both bulk and exfoliated materials, revealing a large nonlinear optical response of BiTeI flakes due to the presence of strong quantum confinement effects and the absence of typical phase-matching requirements encountered in bulk nonlinear crystals. We estimated a second-order nonlinearity at 0.8 eV of |chi((2))| & SIM; 1 nm V-1, which is 10 times larger than in bulk BiTeI crystals and is of the same order of magnitude as in other semiconducting monolayers (e.g., MoS2)

Preparation of bactericidal cationic PDMS surfaces using a facile and efficient approach

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grecs: A group recommendation system based on user clustering

Abstract. In this demonstration paper, we present gRecs, a system for group recommendations that follows a collaborative strategy. We enhance recommendations with the notion of support to model the confidence of the recommendations. Moreover, we propose partitioning users into clusters of similar ones. This way, recommendations for users are produced with respect to the preferences of their cluster members without extensively searching for similar users in the whole user base. Finally, we leverage the power of a top-k algorithm for locating the top-k group recommendations.

Density-based projected clustering over high dimensional data streams

Clustering of high dimensional data streams is an important problem in many application domains, a prominent example being network monitoring. Several approaches have been lately proposed for solving independently the different aspects of the problem. There exist methods for clustering over full dimensional streams and methods for finding clusters in subspaces of high dimensional static data. Yet only a few approaches have been proposed so far which tackle both the stream and the high dimensionality aspects of the problem simultaneously. In this work, we propose a new density-based projected clustering algorithm, HDDStream, for high dimensional data streams. Our algorithm summarizes both the data points and the dimensions where these points are grouped together and maintains these summaries online, as new points arrive over time and old points expire due to ageing. Our experimental results illustrate the effectiveness and the efficiency of HDDStream and also demonstrate that it could serve as a trigger for detecting drastic changes in the underlying stream population, like bursts of network attacks.

Biomimetic engineering of non-adhesive glycocalyx-like PDMS surfaces

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A Rat Model of Central Venous Catheter to Study Establishment of Long-Term Bacterial Biofilm and Related Acute and Chronic Infections

International audienceFormation of resilient biofilms on medical devices colonized by pathogenic microorganisms is a major cause of health-care associated infection. While in vitro biofilm analyses led to promising anti-biofilm approaches, little is known about their translation to in vivo situations and on host contribution to the in vivo dynamics of infections on medical devices. Here we have developed an in vivo model of long-term bacterial biofilm infections in a pediatric totally implantable venous access port (TIVAP) surgically placed in adult rats. Using non-invasive and quantitative bioluminescence, we studied TIVAP contamination by clinically relevant pathogens, Escherichia coli , Pseudomonas aeruginosa , Staphylococcus aureus and Staphylococcus epidermidis , and we demonstrated that TIVAP bacterial populations display typical biofilm phenotypes. In our study, we showed that immunocompetent rats were able to control the colonization and clear the bloodstream infection except for up to 30% that suffered systemic infection and death whereas none of the immunosuppressed rats survived the infection. Besides, we mimicked some clinically relevant TIVAP associated complications such as port-pocket infection and hematogenous route of colonization. Finally, by assessing an optimized antibiotic lock therapy, we established that our in vivo model enables to assess innovative therapeutic strategies against bacterial biofilm infections

<i>In vivo</i> efficacy of ALT.

<p>ALT was instilled in the implanted colonized TIVAP (0 h) and associated with systemic vancomycin to treat <i>S. aureus</i> biofilm colonization. ALT was renewed every 24 h and its efficacy was monitored as photon emissions. Rats (n = 4, for each treatment) were sacrificed after 120 h of treatment and analyzed. (A) 5 mg/mL cefazolin ALT. (B) 1 mg/mL gentamicin ALT. (C) Combined cefazolin and gentamicin ALT (1∶1 v/v). (D–E) TIVAP were aseptically removed and photon emission due to remnant biofilm measured. (D) Cefazolin-treated TIVAP, (E) gentamicin-treated TIVAP and (F) TIVAP treated with cefazolin and gentamicin combination. In (A) to (F) representative experiments are shown. (G) TIVAP was extracted after treatment and cells were harvested and plated for CFU/mL. All the values are mean +/− standard deviation. Statistical analysis was done using one-way analysis of variance (ANOVA) using Graphpad Prism version 5.0c. p value<0.05 considered significant, *** (p<0.0001), ** (p<0.001) and * (p<0.05).</p

Bacterial colonization of TIVAP leads to biofilm formation.

<p>Rats were sacrificed 10 days post infection, TIVAP were removed aseptically and cells harvested from the catheter and port separately and plated on LB agar (E.c., <i>E. coli</i> n = 5 or P.a., <i>P. aeruginosa</i> n = 7) or TSB agar (S.a., <i>S. aureus</i> n = 6 or S.e., <i>S. epidermidis</i> n = 5) plates for CFU/mL (A). (B–E) SEM images confirming true biofilm formation in TIVAP <i>in vivo</i> in the port and catheter. Representative images are presented. White arrows indicate eukaryotic immune cells.</p

Immunosuppression led to fatal biofilm infection.

<p>(A) 10² CFU in 100 µL of the different bacteria were injected into the port of TIVAP implanted in cyclophosphamide-treated rats (100 mg/kg day -4 and 50 mg/kg day -1 of inoculation) and photon emission was monitored up to the death of the animals on days 3/5 to evaluate biofilm formation and associated infection. TIVAP were aseptically removed from dead animals and photon emission measured for both the animal and the extracted TIVAP. Control rat was a catheterized and cyclophosphamide-treated but without bacterial inoculation. (B) SEM images of TIVAP (port and catheter) infected with 4 clinical strains used in this study. Number of rats (n) used in the experiment, n = 4 for each strain.</p